1
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Tower J. Selectively advantageous instability in biotic and pre-biotic systems and implications for evolution and aging. FRONTIERS IN AGING 2024; 5:1376060. [PMID: 38818026 PMCID: PMC11137231 DOI: 10.3389/fragi.2024.1376060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 04/15/2024] [Indexed: 06/01/2024]
Abstract
Rules of biology typically involve conservation of resources. For example, common patterns such as hexagons and logarithmic spirals require minimal materials, and scaling laws involve conservation of energy. Here a relationship with the opposite theme is discussed, which is the selectively advantageous instability (SAI) of one or more components of a replicating system, such as the cell. By increasing the complexity of the system, SAI can have benefits in addition to the generation of energy or the mobilization of building blocks. SAI involves a potential cost to the replicating system for the materials and/or energy required to create the unstable component, and in some cases, the energy required for its active degradation. SAI is well-studied in cells. Short-lived transcription and signaling factors enable a rapid response to a changing environment, and turnover is critical for replacement of damaged macromolecules. The minimal gene set for a viable cell includes proteases and a nuclease, suggesting SAI is essential for life. SAI promotes genetic diversity in several ways. Toxin/antitoxin systems promote maintenance of genes, and SAI of mitochondria facilitates uniparental transmission. By creating two distinct states, subject to different selective pressures, SAI can maintain genetic diversity. SAI of components of synthetic replicators favors replicator cycling, promoting emergence of replicators with increased complexity. Both classical and recent computer modeling of replicators reveals SAI. SAI may be involved at additional levels of biological organization. In summary, SAI promotes replicator genetic diversity and reproductive fitness, and may promote aging through loss of resources and maintenance of deleterious alleles.
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Affiliation(s)
- John Tower
- Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, United States
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2
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Andreas E, Cummins B, Gedeon T. Quantifying robustness of the gap gene network. J Theor Biol 2024; 580:111720. [PMID: 38211890 DOI: 10.1016/j.jtbi.2024.111720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Revised: 12/28/2023] [Accepted: 12/30/2023] [Indexed: 01/13/2024]
Abstract
Early development of Drosophila melanogaster (fruit fly) facilitated by the gap gene network has been shown to be incredibly robust, and the same patterns emerge even when the process is seriously disrupted. We investigate this robustness using a previously developed computational framework called DSGRN (Dynamic Signatures Generated by Regulatory Networks). Our mathematical innovations include the conceptual extension of this established modeling technique to enable modeling of spatially monotone environmental effects, as well as the development of a collection of graph theoretic robustness scores for network models. This allows us to rank order the robustness of network models of cellular systems where each cell contains the same genetic network topology but operates under a parameter regime that changes continuously from cell to cell. We demonstrate the power of this method by comparing the robustness of two previously introduced network models of gap gene expression along the anterior-posterior axis of the fruit fly embryo, both to each other and to a random sample of networks with same number of nodes and edges. We observe that there is a substantial difference in robustness scores between the two models. Our biological insight is that random network topologies are in general capable of reproducing complex patterns of expression, but that using measures of robustness to rank order networks permits a large reduction in hypothesis space for highly conserved systems such as developmental networks.
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Affiliation(s)
- Elizabeth Andreas
- Department of Mathematical Sciences, Montana State University, Bozeman, 59718, MT, USA.
| | - Breschine Cummins
- Department of Mathematical Sciences, Montana State University, Bozeman, 59718, MT, USA
| | - Tomáš Gedeon
- Department of Mathematical Sciences, Montana State University, Bozeman, 59718, MT, USA
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3
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Munshi R, Ling J, Ryabichko S, Wieschaus E, Gregor T. Transcription factor clusters as information transfer agents. ARXIV 2024:arXiv:2403.02943v1. [PMID: 38495568 PMCID: PMC10942473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Deciphering how genes interpret information from the concentration of transcription factors (TFs) within the cell nucleus remains a fundamental question in gene regulation. Recent advancements have unveiled the heterogeneous distribution of TF molecules in the nucleus, posing challenges to the precise decoding of concentration signals. To explore this phenomenon, we employ high-resolution single-cell imaging of a fluorescently tagged TF protein, Bicoid, in living fly embryos. We show that accumulation of Bicoid in submicron clusters preserves the spatial information of the maternal Bicoid gradient, and that cluster intensity, size, and frequency offer remarkably precise spatial cues. We further discover that various known gene targets of Bicoid activation colocalize with clusters and that for the target gene Hunchback, this colocalization is dependent on its enhancer binding affinity. Modeling information transfer through these clusters suggests that clustering offers a more rapid sensing mechanism for global nuclear concentrations than freely diffusing TF molecules detected by simple enhancers.
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Affiliation(s)
- Rahul Munshi
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Jia Ling
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Sergey Ryabichko
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Eric Wieschaus
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
- Department of Molecular Biology and Howard Hughes Medical Institute, Princeton University, Princeton, NJ 08544, USA
| | - Thomas Gregor
- Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
- Department of Stem Cell and Developmental Biology, CNRS UMR3738 Paris Cité, Institut Pasteur, 25 rue du Docteur Roux, 75015 Paris, France
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4
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Lin S, Lim B. Multifaceted effects on even-skipped transcriptional dynamics upon Krüppel dosage changes. Development 2024; 151:dev202132. [PMID: 38345298 PMCID: PMC10948998 DOI: 10.1242/dev.202132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Accepted: 02/08/2024] [Indexed: 03/05/2024]
Abstract
Although fluctuations in transcription factor (TF) dosage are often well tolerated, TF dosage modulation can change the target gene expression dynamics and result in significant non-lethal developmental phenotypes. Using MS2/MCP-mediated quantitative live imaging in early Drosophila embryos, we analyzed how changing levels of the gap gene Krüppel (Kr) affects transcriptional dynamics of the pair-rule gene even-skipped (eve). Halving the Kr dosage leads to a transient posterior expansion of the eve stripe 2 and an anterior shift of stripe 5. Surprisingly, the most significant changes are observed in eve stripes 3 and 4, the enhancers of which do not contain Kr-binding sites. In Kr heterozygous embryos, both stripes 3 and 4 display narrower widths, anteriorly shifted boundaries and reduced mRNA production levels. We show that Kr dosage indirectly affects stripe 3 and 4 dynamics by modulating other gap gene dynamics. We quantitatively correlate moderate body segment phenotypes of Kr heterozygotes with spatiotemporal changes in eve expression. Our results indicate that nonlinear relationships between TF dosage and phenotypes underlie direct TF-DNA and indirect TF-TF interactions.
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Affiliation(s)
- Shufan Lin
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Bomyi Lim
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
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5
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Filippopoulou K, Konstantinides N. Evolution of patterning. FEBS J 2024; 291:663-671. [PMID: 37943156 DOI: 10.1111/febs.16995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Revised: 09/28/2023] [Accepted: 11/07/2023] [Indexed: 11/10/2023]
Abstract
Developing tissues are patterned in space and time; this enables them to differentiate their cell types and form complex structures to support different body plans. Although space and time are two independent entities, there are many examples of spatial patterns that originate from temporal ones. The most prominent example is the expression of the genes hunchback, Krüppel, pdm, and castor, which are expressed temporally in the neural stem cells of the Drosophila ventral nerve cord and spatially along the anteroposterior axis of the blastoderm stage embryo. In this Viewpoint, we investigate the relationship between space and time in specific examples of spatial and temporal patterns with the aim of gaining insight into the evolutionary history of patterning.
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6
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Masuda LHP, Sabino AU, Reinitz J, Ramos AF, Machado-Lima A, Andrioli LP. Global repression by tailless during segmentation. Dev Biol 2024; 505:11-23. [PMID: 37879494 PMCID: PMC10949167 DOI: 10.1016/j.ydbio.2023.09.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2022] [Revised: 09/26/2023] [Accepted: 09/28/2023] [Indexed: 10/27/2023]
Abstract
The orphan nuclear receptor Tailless (Tll) exhibits conserved roles in brain formation and maintenance that are shared, for example, with vertebrate orthologous forms (Tlx). However, the early expression of tll in two gap domains in the segmentation cascade of Drosophila is unusual even for most other insects. Here we investigate tll regulation on pair-rule stripes. With ectopic misexpression of tll we detected unexpected repression of almost all pair-rule stripes of hairy (h), even-skipped (eve), runt (run), and fushi-tarazu (ftz). Examining Tll embryonic ChIP-chip data with regions mapped as Cis-Regulatory Modules (CRMs) of pair-rule stripes we verified Tll interactions to these regions. With the ChIP-chip data we also verified Tll interactions to the CRMs of gap domains and in the misexpression assay, Tll-mediated repression on Kruppel (Kr), kni (kni) and giant (gt) according to their differential sensitivity to Tll. These results with gap genes confirmed previous data from the literature and argue against indirect repression roles of Tll in the striped pattern. Moreover, the prediction of Tll binding sites in the CRMs of eve stripes and the mathematical modeling of their removal using an experimentally validated theoretical framework shows effects on eve stripes compatible with the absence of a repressor binding to the CRMs. In addition, modeling increased tll levels in the embryo results in the differential repression of eve stripes, agreeing well with the results of the misexpression assay. In genetic assays we investigated eve 5, that is strongly repressed by the ectopic domain and representative of more central stripes not previously implied to be under direct regulation of tll. While this stripe is little affected in tll-, its posterior border is expanded in gt- but detected with even greater expansion in gt-;tll-. We end up by discussing tll with key roles in combinatorial repression mechanisms to contain the expression of medial patterns of the segmentation cascade in the extremities of the embryo.
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Affiliation(s)
| | - Alan Utsuni Sabino
- Departamento de Radiologia e Oncologia, Instituto do Câncer do Estado de São Paulo, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil
| | - John Reinitz
- Departments of Statistics, Ecology and Evolution, Molecular Genetics & Cell Biology, Institute of Genomics and Systems Biology, University of Chicago, Chicago, IL, USA
| | | | - Ariane Machado-Lima
- Escola de Artes, Ciências e Humanidades da Universidade de São Paulo, São Paulo, Brazil
| | - Luiz Paulo Andrioli
- Escola de Artes, Ciências e Humanidades da Universidade de São Paulo, São Paulo, Brazil.
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7
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Nikolić M, Antonetti V, Liu F, Muhaxheri G, Petkova MD, Scheeler M, Smith EM, Bialek W, Gregor T. Scale invariance in early embryonic development. ARXIV 2023:arXiv:2312.17684v1. [PMID: 38235065 PMCID: PMC10793483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
The body plan of the fruit fly is determined by the expression of just a handful of genes. We show that the spatial patterns of expression for several of these genes scale precisely with the size of the embryo. Concretely, discrete positional markers such as the peaks in striped patterns have absolute positions along the anterior-posterior axis that are proportional to embryo length, with better than 1% accuracy. Further, the information (in bits) that graded patterns of expression provide about position can be decomposed into information about fractional or scaled position and information about absolute position or embryo length; all of the available information is about scaled position, again with ~ 1% accuracy. These observations suggest that the underlying genetic network exhibits scale invariance in a deeper mathematical sense. Taking this mathematical statement seriously requires that the network dynamics have a zero mode, which connects to many other observations on this system.
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Affiliation(s)
- Miloš Nikolić
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton NJ 08544 USA
| | - Victoria Antonetti
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
- Center for Quantitative Biology and School of Physics, Peking University, Beijing 100871 China
| | - Feng Liu
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton NJ 08544 USA
- Center for Quantitative Biology and School of Physics, Peking University, Beijing 100871 China
| | - Gentian Muhaxheri
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
- Department of Physics, Lehman College, City University of New York, Bronx, NY 10468 USA
| | | | - Martin Scheeler
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
| | - Eric M Smith
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
| | - William Bialek
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton NJ 08544 USA
- Initiative for the Theoretical Sciences, The Graduate Center, City University of New York, 365 Fifth Ave., New York, NY 10016 USA
| | - Thomas Gregor
- Joseph Henry Laboratories of Physics and Princeton University, Princeton NJ 08544 USA
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton NJ 08544 USA
- Department of Developmental and Stem Cell Biology UMR3738, Institut Pasteur, 75015 Paris, France
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8
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Haroush N, Levo M, Wieschaus EF, Gregor T. Functional analysis of the Drosophila eve locus in response to non-canonical combinations of gap gene expression levels. Dev Cell 2023; 58:2789-2801.e5. [PMID: 37890488 PMCID: PMC10872916 DOI: 10.1016/j.devcel.2023.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 08/10/2023] [Accepted: 10/04/2023] [Indexed: 10/29/2023]
Abstract
Transcription factor combinations play a key role in shaping cellular identity. However, the precise relationship between specific combinations and downstream effects remains elusive. Here, we investigate this relationship within the context of the Drosophila eve locus, which is controlled by gap genes. We measure spatiotemporal levels of four gap genes in heterozygous and homozygous gap mutant embryos and correlate them with the striped eve activity pattern. Although changes in gap gene expression extend beyond the manipulated gene, the spatial patterns of Eve expression closely mirror canonical activation levels in wild type. Interestingly, some combinations deviate from the wild-type repertoire but still drive eve activation. Although in homozygous mutants some Eve stripes exhibit partial penetrance, stripes consistently emerge at reproducible positions, even with varying gap gene levels. Our findings suggest a robust molecular canalization of cell fates in gap mutants and provide insights into the regulatory constraints governing multi-enhancer gene loci.
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Affiliation(s)
- Netta Haroush
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Michal Levo
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Eric F Wieschaus
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Department of Molecular Biology and Howard Hughes Medical Institute, Princeton University, Princeton, NJ 08544, USA
| | - Thomas Gregor
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA; Department of Stem Cell and Developmental Biology, CNRS UMR3738 Paris Cité, Institut Pasteur, 75015 Paris, France.
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9
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Moudgil A, Sobti RC, Kaur T. In-silico identification and comparison of transcription factor binding sites cluster in anterior-posterior patterning genes in Drosophila melanogaster and Tribolium castaneum. PLoS One 2023; 18:e0290035. [PMID: 37590227 PMCID: PMC10434971 DOI: 10.1371/journal.pone.0290035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2023] [Accepted: 07/26/2023] [Indexed: 08/19/2023] Open
Abstract
The cis-regulatory data that help in transcriptional regulation is arranged into modular pieces of a few hundred base pairs called CRMs (cis-regulatory modules) and numerous binding sites for multiple transcription factors are prominent characteristics of these cis-regulatory modules. The present study was designed to localize transcription factor binding site (TFBS) clusters on twelve Anterior-posterior (A-P) genes in Tribolium castaneum and compare them to their orthologous gene enhancers in Drosophila melanogaster. Out of the twelve A-P patterning genes, six were gap genes (Kruppel, Knirps, Tailless, Hunchback, Giant, and Caudal) and six were pair rule genes (Hairy, Runt, Even-skipped, Fushi-tarazu, Paired, and Odd-skipped). The genes along with 20 kb upstream and downstream regions were scanned for TFBS clusters using the Motif Cluster Alignment Search Tool (MCAST), a bioinformatics tool that looks for set of nucleotide sequences for statistically significant clusters of non-overlapping occurrence of a given set of motifs. The motifs used in the current study were Hunchback, Caudal, Giant, Kruppel, Knirps, and Even-skipped. The results of the MCAST analysis revealed the maximum number of TFBS for Hunchback, Knirps, Caudal, and Kruppel in both D. melanogaster and T. castaneum, while Bicoid TFBS clusters were found only in D. melanogaster. The size of all the predicted TFBS clusters was less than 1kb in both insect species. These sequences revealed more transversional sites (Tv) than transitional sites (Ti) and the average Ti/Tv ratio was 0.75.
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Affiliation(s)
- Anshika Moudgil
- Department of Zoology, DAV University, Jalandhar, Punjab, India
| | | | - Tejinder Kaur
- Department of Zoology, DAV University, Jalandhar, Punjab, India
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10
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Jacobs J, Pagani M, Wenzl C, Stark A. Widespread regulatory specificities between transcriptional co-repressors and enhancers in Drosophila. Science 2023; 381:198-204. [PMID: 37440660 DOI: 10.1126/science.adf6149] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 06/13/2023] [Indexed: 07/15/2023]
Abstract
Gene expression is controlled by the precise activation and repression of transcription. Repression is mediated by specialized transcription factors (TFs) that recruit co-repressors (CoRs) to silence transcription, even in the presence of activating cues. However, whether CoRs can dominantly silence all enhancers or display distinct specificities is unclear. In this work, we report that most enhancers in Drosophila can be repressed by only a subset of CoRs, and enhancers classified by CoR sensitivity show distinct chromatin features, function, TF motifs, and binding. Distinct TF motifs render enhancers more resistant or sensitive to specific CoRs, as we demonstrate by motif mutagenesis and addition. These CoR-enhancer compatibilities constitute an additional layer of regulatory specificity that allows differential regulation at close genomic distances and is indicative of distinct mechanisms of transcriptional repression.
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Affiliation(s)
- Jelle Jacobs
- Research Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), Campus-Vienna-Biocenter 1, Vienna, Austria
| | - Michaela Pagani
- Research Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), Campus-Vienna-Biocenter 1, Vienna, Austria
| | - Christoph Wenzl
- Research Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), Campus-Vienna-Biocenter 1, Vienna, Austria
| | - Alexander Stark
- Research Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), Campus-Vienna-Biocenter 1, Vienna, Austria
- Medical University of Vienna, Vienna BioCenter (VBC), Vienna, Austria
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11
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Sakaguchi S, Mizuno S, Okochi Y, Tanegashima C, Nishimura O, Uemura T, Kadota M, Naoki H, Kondo T. Single-cell transcriptome atlas of Drosophila gastrula 2.0. Cell Rep 2023:112707. [PMID: 37433294 DOI: 10.1016/j.celrep.2023.112707] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 03/27/2023] [Accepted: 06/13/2023] [Indexed: 07/13/2023] Open
Abstract
During development, positional information directs cells to specific fates, leading them to differentiate with their own transcriptomes and express specific behaviors and functions. However, the mechanisms underlying these processes in a genome-wide view remain ambiguous, partly because the single-cell transcriptomic data of early developing embryos containing accurate spatial and lineage information are still lacking. Here, we report a single-cell transcriptome atlas of Drosophila gastrulae, divided into 77 transcriptomically distinct clusters. We find that the expression profiles of plasma-membrane-related genes, but not those of transcription-factor genes, represent each germ layer, supporting the nonequivalent contribution of each transcription-factor mRNA level to effector gene expression profiles at the transcriptome level. We also reconstruct the spatial expression patterns of all genes at the single-cell stripe level as the smallest unit. This atlas is an important resource for the genome-wide understanding of the mechanisms by which genes cooperatively orchestrate Drosophila gastrulation.
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Affiliation(s)
- Shunta Sakaguchi
- Laboratory of Cell Recognition and Pattern Formation, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Sonoko Mizuno
- Laboratory of Cell Recognition and Pattern Formation, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Yasushi Okochi
- Laboratory of Theoretical Biology, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Chiharu Tanegashima
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research, Chuo-ku, Kobe, Hyogo 650-0047, Japan
| | - Osamu Nishimura
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research, Chuo-ku, Kobe, Hyogo 650-0047, Japan
| | - Tadashi Uemura
- Laboratory of Cell Recognition and Pattern Formation, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; Center for Living Systems Information Science, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Mitsutaka Kadota
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research, Chuo-ku, Kobe, Hyogo 650-0047, Japan
| | - Honda Naoki
- Laboratory of Theoretical Biology, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; Laboratory of Data-driven Biology, Graduate School of Integrated Sciences for Life, Hiroshima University, Higashihiroshima, Hiroshima 739-8511, Japan; Theoretical Biology Research Group, Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8585, Japan
| | - Takefumi Kondo
- Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; The Keihanshin Consortium for Fostering the Next Generation of Global Leaders in Research (K-CONNEX), Sakyo-ku, Kyoto 606-8501, Japan.
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12
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Santos-Moreno J, Tasiudi E, Kusumawardhani H, Stelling J, Schaerli Y. Robustness and innovation in synthetic genotype networks. Nat Commun 2023; 14:2454. [PMID: 37117168 PMCID: PMC10147661 DOI: 10.1038/s41467-023-38033-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Accepted: 04/13/2023] [Indexed: 04/30/2023] Open
Abstract
Genotype networks are sets of genotypes connected by small mutational changes that share the same phenotype. They facilitate evolutionary innovation by enabling the exploration of different neighborhoods in genotype space. Genotype networks, first suggested by theoretical models, have been empirically confirmed for proteins and RNAs. Comparative studies also support their existence for gene regulatory networks (GRNs), but direct experimental evidence is lacking. Here, we report the construction of three interconnected genotype networks of synthetic GRNs producing three distinct phenotypes in Escherichia coli. Our synthetic GRNs contain three nodes regulating each other by CRISPR interference and governing the expression of fluorescent reporters. The genotype networks, composed of over twenty different synthetic GRNs, provide robustness in face of mutations while enabling transitions to innovative phenotypes. Through realistic mathematical modeling, we quantify robustness and evolvability for the complete genotype-phenotype map and link these features mechanistically to GRN motifs. Our work thereby exemplifies how GRN evolution along genotype networks might be driving evolutionary innovation.
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Affiliation(s)
- Javier Santos-Moreno
- Department of Fundamental Microbiology, University of Lausanne, Biophore Building, 1015, Lausanne, Switzerland
- Department of Medicine and Life Sciences, Pompeu Fabra University, 00803, Barcelona, Spain
| | - Eve Tasiudi
- Department of Biosystems Science and Engineering, ETH Zurich and SIB Swiss Institute of Bioinformatics, Basel, Switzerland
| | - Hadiastri Kusumawardhani
- Department of Fundamental Microbiology, University of Lausanne, Biophore Building, 1015, Lausanne, Switzerland
| | - Joerg Stelling
- Department of Biosystems Science and Engineering, ETH Zurich and SIB Swiss Institute of Bioinformatics, Basel, Switzerland.
| | - Yolanda Schaerli
- Department of Fundamental Microbiology, University of Lausanne, Biophore Building, 1015, Lausanne, Switzerland.
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13
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Forbes Beadle L, Zhou H, Rattray M, Ashe HL. Modulation of transcription burst amplitude underpins dosage compensation in the Drosophila embryo. Cell Rep 2023; 42:112382. [PMID: 37060568 PMCID: PMC10283159 DOI: 10.1016/j.celrep.2023.112382] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Revised: 02/03/2023] [Accepted: 03/27/2023] [Indexed: 04/16/2023] Open
Abstract
Dosage compensation, the balancing of X-linked gene expression between sexes and to the autosomes, is critical to an organism's fitness and survival. In Drosophila, dosage compensation involves hypertranscription of the male X chromosome. Here, we use quantitative live imaging and modeling at single-cell resolution to study X chromosome dosage compensation in Drosophila. We show that the four X chromosome genes studied undergo transcriptional bursting in male and female embryos. Mechanistically, our data reveal that transcriptional upregulation of male X chromosome genes is primarily mediated by a higher RNA polymerase II initiation rate and burst amplitude across the expression domain. In contrast, burst frequency is spatially modulated in nuclei within the expression domain in response to different transcription factor concentrations to tune the transcriptional response. Together, these data show how the local and global regulation of distinct burst parameters can establish the complex transcriptional outputs underpinning developmental patterning.
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Affiliation(s)
- Lauren Forbes Beadle
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, UK
| | - Hongpeng Zhou
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, UK
| | - Magnus Rattray
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, UK.
| | - Hilary L Ashe
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, UK.
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14
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Cheatle Jarvela AM, Trelstad CS, Pick L. Anterior-posterior patterning of segments in Anopheles stephensi offers insights into the transition from sequential to simultaneous segmentation in holometabolous insects. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART B, MOLECULAR AND DEVELOPMENTAL EVOLUTION 2023; 340:116-130. [PMID: 34734470 PMCID: PMC9061899 DOI: 10.1002/jez.b.23102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 10/13/2021] [Accepted: 10/16/2021] [Indexed: 11/10/2022]
Abstract
The gene regulatory network for segmentation in arthropods offers valuable insights into how networks evolve owing to the breadth of species examined and the extremely detailed knowledge gained in the model organism Drosophila melanogaster. These studies have shown that Drosophila's network represents a derived state that acquired changes to accelerate segment patterning, whereas most insects specify segments gradually as the embryo elongates. Such heterochronic shifts in segmentation have potentially emerged multiple times within holometabolous insects, resulting in many mechanistic variants and difficulties in isolating underlying commonalities that permit such shifts. Recent studies identified regulatory genes that work as timing factors, coordinating gene expression transitions during segmentation. These studies predict that changes in timing factor deployment explain shifts in segment patterning relative to other developmental events. Here, we test this hypothesis by characterizing the temporal and spatial expression of the pair-rule patterning genes in the malaria vector mosquito, Anopheles stephensi. This insect is a Dipteran (fly), like Drosophila, but represents an ancient divergence within this clade, offering a useful counterpart for evo-devo studies. In mosquito embryos, we observe anterior to posterior sequential addition of stripes for many pair-rule genes and a wave of broad timer gene expression across this axis. Segment polarity gene stripes are added sequentially in the wake of the timer gene wave and the full pattern is not complete until the embryo is fully elongated. This "progressive segmentation" mode in Anopheles displays commonalities with both Drosophila's rapid segmentation mechanism and sequential modes used by more distantly related insects.
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Affiliation(s)
- Alys M. Cheatle Jarvela
- Department of Entomology, University of Maryland, College Park, 4291 Fieldhouse Drive, College Park, MD 20742, U.S.A
| | - Catherine S. Trelstad
- Department of Entomology, University of Maryland, College Park, 4291 Fieldhouse Drive, College Park, MD 20742, U.S.A
| | - Leslie Pick
- Department of Entomology, University of Maryland, College Park, 4291 Fieldhouse Drive, College Park, MD 20742, U.S.A
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15
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Computational approaches to understand transcription regulation in development. Biochem Soc Trans 2023; 51:1-12. [PMID: 36695505 PMCID: PMC9988001 DOI: 10.1042/bst20210145] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Revised: 01/07/2023] [Accepted: 01/13/2023] [Indexed: 01/26/2023]
Abstract
Gene regulatory networks (GRNs) serve as useful abstractions to understand transcriptional dynamics in developmental systems. Computational prediction of GRNs has been successfully applied to genome-wide gene expression measurements with the advent of microarrays and RNA-sequencing. However, these inferred networks are inaccurate and mostly based on correlative rather than causative interactions. In this review, we highlight three approaches that significantly impact GRN inference: (1) moving from one genome-wide functional modality, gene expression, to multi-omics, (2) single cell sequencing, to measure cell type-specific signals and predict context-specific GRNs, and (3) neural networks as flexible models. Together, these experimental and computational developments have the potential to significantly impact the quality of inferred GRNs. Ultimately, accurately modeling the regulatory interactions between transcription factors and their target genes will be essential to understand the role of transcription factors in driving developmental gene expression programs and to derive testable hypotheses for validation.
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16
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Lee K, O’Neill KM, Ku J, Shvartsman SY, Kim Y. Patterning potential of the terminal system in the Drosophila embryo. KOREAN J CHEM ENG 2023. [DOI: 10.1007/s11814-022-1298-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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17
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Xu R, Dai F, Wu H, Jiao R, He F, Ma J. Shaping the scaling characteristics of gap gene expression patterns in Drosophila. Heliyon 2023; 9:e13623. [PMID: 36879745 PMCID: PMC9984453 DOI: 10.1016/j.heliyon.2023.e13623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Revised: 01/25/2023] [Accepted: 02/06/2023] [Indexed: 02/11/2023] Open
Abstract
How patterns are formed to scale with tissue size remains an unresolved problem. Here we investigate embryonic patterns of gap gene expression along the anterior-posterior (AP) axis in Drosophila. We use embryos that greatly differ in length and, importantly, possess distinct length-scaling characteristics of the Bicoid (Bcd) gradient. We systematically analyze the dynamic movements of gap gene expression boundaries in relation to both embryo length and Bcd input as a function of time. We document the process through which such dynamic movements drive both an emergence of a global scaling landscape and evolution of boundary-specific scaling characteristics. We show that, despite initial differences in pattern scaling characteristics that mimic those of Bcd in the anterior, such characteristics of final patterns converge. Our study thus partitions the contributions of Bcd input and regulatory dynamics inherent to the AP patterning network in shaping embryonic pattern's scaling characteristics.
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Affiliation(s)
- Ruoqing Xu
- Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China
- Institute of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China
| | - Fei Dai
- Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Honggang Wu
- Sino-French Hoffmann Institute, School of Basic Medical Science, Guangzhou Medical University, Guangzhou 510182, China
- Key Laboratory of Interdisciplinary Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Renjie Jiao
- Sino-French Hoffmann Institute, School of Basic Medical Science, Guangzhou Medical University, Guangzhou 510182, China
- Key Laboratory of Interdisciplinary Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Feng He
- Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China
- Institute of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China
- Corresponding author. Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China.
| | - Jun Ma
- Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China
- Institute of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China
- Joint Institute of Genetics and Genome Medicine between Zhejiang University and University of Toronto, Hangzhou, Zhejiang, China
- Corresponding author. Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, China.
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18
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Clark E, Battistara M, Benton MA. A timer gene network is spatially regulated by the terminal system in the Drosophila embryo. eLife 2022; 11:e78902. [PMID: 36524728 PMCID: PMC10065802 DOI: 10.7554/elife.78902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Accepted: 12/15/2022] [Indexed: 12/23/2022] Open
Abstract
In insect embryos, anteroposterior patterning is coordinated by the sequential expression of the 'timer' genes caudal, Dichaete, and odd-paired, whose expression dynamics correlate with the mode of segmentation. In Drosophila, the timer genes are expressed broadly across much of the blastoderm, which segments simultaneously, but their expression is delayed in a small 'tail' region, just anterior to the hindgut, which segments during germband extension. Specification of the tail and the hindgut depends on the terminal gap gene tailless, but beyond this the regulation of the timer genes is poorly understood. We used a combination of multiplexed imaging, mutant analysis, and gene network modelling to resolve the regulation of the timer genes, identifying 11 new regulatory interactions and clarifying the mechanism of posterior terminal patterning. We propose that a dynamic Tailless expression gradient modulates the intrinsic dynamics of a timer gene cross-regulatory module, delineating the tail region and delaying its developmental maturation.
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Affiliation(s)
- Erik Clark
- Department of Zoology, University of CambridgeCambridgeUnited Kingdom
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
- Department of Genetics, University of CambridgeCambridgeUnited Kingdom
| | - Margherita Battistara
- Department of Zoology, University of CambridgeCambridgeUnited Kingdom
- Department of Physiology, Development and Neuroscience, University of CambridgeCambridgeUnited Kingdom
| | - Matthew A Benton
- Department of Zoology, University of CambridgeCambridgeUnited Kingdom
- Developmental Biology Unit, EMBLHeidelbergGermany
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19
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Saha S, Moon HR, Han B, Mugler A. Deduction of signaling mechanisms from cellular responses to multiple cues. NPJ Syst Biol Appl 2022; 8:48. [PMID: 36450797 PMCID: PMC9712676 DOI: 10.1038/s41540-022-00262-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Accepted: 11/08/2022] [Indexed: 12/05/2022] Open
Abstract
Cell signaling networks are complex and often incompletely characterized, making it difficult to obtain a comprehensive picture of the mechanisms they encode. Mathematical modeling of these networks provides important clues, but the models themselves are often complex, and it is not always clear how to extract falsifiable predictions. Here we take an inverse approach, using experimental data at the cell level to deduce the minimal signaling network. We focus on cells' response to multiple cues, specifically on the surprising case in which the response is antagonistic: the response to multiple cues is weaker than the response to the individual cues. We systematically build candidate signaling networks one node at a time, using the ubiquitous ingredients of (i) up- or down-regulation, (ii) molecular conversion, or (iii) reversible binding. In each case, our method reveals a minimal, interpretable signaling mechanism that explains the antagonistic response. Our work provides a systematic way to deduce molecular mechanisms from cell-level data.
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Affiliation(s)
- Soutick Saha
- grid.169077.e0000 0004 1937 2197Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 USA
| | - Hye-ran Moon
- grid.169077.e0000 0004 1937 2197School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907 USA
| | - Bumsoo Han
- grid.169077.e0000 0004 1937 2197School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907 USA ,grid.169077.e0000 0004 1937 2197Purdue Center for Cancer Research, Purdue University, West Lafayette, IN 47907 USA
| | - Andrew Mugler
- grid.169077.e0000 0004 1937 2197Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 USA ,grid.169077.e0000 0004 1937 2197Purdue Center for Cancer Research, Purdue University, West Lafayette, IN 47907 USA ,grid.21925.3d0000 0004 1936 9000Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 USA
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20
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Zhu H, Shen W, Luo C, Liu F. An integrated microfluidic device for multiplexed imaging of spatial gene expression patterns of Drosophila embryos. LAB ON A CHIP 2022; 22:4081-4092. [PMID: 36165088 DOI: 10.1039/d2lc00514j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
To reveal the underlying mechanism of the biological function of multicellular systems, it is important to obtain comprehensive spatial gene expression profiles. Among the emerging single-cell spatial-omics techniques, immunofluorescence (IF)-based iterative multiplexed imaging is a promising approach. However, the conventional method is usually costly, time-consuming, labor-intensive, and has low throughput. Moreover, it has yet to be demonstrated in intact multicellular organisms. Here, we developed an integrated microfluidic system to overcome these challenges for quantitatively measuring multiple protein profiles sequentially in situ in the same Drosophila embryo. We designed an array of hydrodynamic trapping sites to automatically capture over ten Drosophila embryos with orientation selectivity at more than 90% trapping rates. We also optimized the geometry of confinement and the on-chip IF protocol to achieve the same high signal-to-noise ratio as the off-chip traditional IF experiments. Moreover, we developed an efficient de-staining protocol by combining on-chip antibody stripping and fluorophore bleaching. Using the same secondary antibody to sequentially stain different genes, we confirmed that the de-stained genes have no detectable interference with the subsequently stained genes, and the gene expression profiles are preserved after multiple cycles of staining and de-staining processes. This preliminary test shows that our newly developed integrated microfluidic system can be a powerful tool for multiplexed imaging of Drosophila embryos. Our work opens a new avenue to design microfluidic chips for multicellular organisms and single-cell spatial-omics techniques.
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Affiliation(s)
- Hongcun Zhu
- The State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing, 100871, China.
| | - Wenting Shen
- Center for Quantitative Biology, Peking University, Beijing, 100871, China.
| | - Chunxiong Luo
- The State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing, 100871, China.
- Center for Quantitative Biology, Peking University, Beijing, 100871, China.
- Wenzhou Institute University of Chinese Academy of Sciences, Wenzhou, Zhejiang, China
| | - Feng Liu
- Center for Quantitative Biology, Peking University, Beijing, 100871, China.
- Key Laboratory of Hebei Province for Molecular Biophysics, Institute of Biophysics, School of Health Science & Biomedical Engineering, Hebei University of Technology, Tianjin, 300130, China
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21
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Jäkel AC, Aufinger L, Simmel FC. Steady-State Operation of a Cell-Free Genetic Band-Detection Circuit. ACS Synth Biol 2022; 11:3273-3284. [PMID: 36095299 DOI: 10.1021/acssynbio.2c00195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Pattern formation processes play a decisive role during embryogenesis and involve the precise spatial and temporal orchestration of intricate gene regulatory processes. Synthetic gene circuits modeled after their biological counterparts can be used to investigate such processes under well-controlled conditions and may, in the future, be utilized for autonomous position determination in synthetic biological materials. Here, we investigated a three-node feed-forward gene regulatory circuit in vitro that generates three distinct fluorescent outputs in response to varying concentrations of a single externally supplied morphogen. The circuit acts as a band detector for the morphogen concentration and, in a spatial context, could serve as a stripe-forming gene circuit. We simulated the behavior of the genetic circuit in the presence of a morphogen gradient using a system of ordinary differential equations and determined optimal parameters for stripe-pattern formation using an evolutionary algorithm. To analyze the subcircuits of the system, we conducted cell-free characterization experiments and finally tested the whole genetic circuit in nanoliter-scale microfluidic flow reactors that provided a continuous supply of cell extract and metabolites and allowed removal of degradation products. To make use of the widely employed promoters PLlacO-1 and PLtetO-1 in our design, we removed LacI from our bacterial cell extract by genome engineering Escherichia coli using a pORTMAGE workflow. Our results show that the band-detector works as designed when operated out of equilibrium within the flow reactors. On the other hand, subcircuits of the system and the whole circuit fail to generate the desired gene expression response when operated in a closed reactor. Our work thus underlines the importance of out-of-equilibrium operation of complex gene circuits, which cannot settle to a steady-state expression pattern within the finite lifetime of a cell-free expression system.
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Affiliation(s)
- Anna C Jäkel
- Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching D-85748, Germany
| | - Lukas Aufinger
- Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching D-85748, Germany
| | - Friedrich C Simmel
- Department of Bioscience, School of Natural Sciences, Technical University of Munich, Garching D-85748, Germany
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22
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Baltruk LJ, Lavezzo GM, Machado-Lima A, Digiampietri LA, Andrioli LP. An additive repression mechanism sets the anterior limits of anterior pair-rule stripes 1. Cells Dev 2022; 171:203802. [PMID: 35934285 DOI: 10.1016/j.cdev.2022.203802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 01/25/2023]
Abstract
Segments are repeated anatomical units forming the body of insects. In Drosophila, the specification of the body takes place during the blastoderm through the segmentation cascade. Pair-rule genes such as hairy (h), even-skipped (eve), runt (run), and fushi-tarazu (ftz) are of the intermediate level of the cascade and each pair-rule gene is expressed in seven transversal stripes along the antero-posterior axis of the embryo. Stripes are formed by independent cis-regulatory modules (CRMs) under the regulation of transcription factors of maternal source and of gap proteins of the first level of the cascade. The initial blastoderm of Drosophila is a syncytium and it also coincides with the mid-blastula transition when thousands of zygotic genes are transcribed and their products are able to diffuse in the cytoplasm. Thus, we anticipated a complex regulation of the CRMs of the pair-rule stripes. The CRMs of h 1, eve 1, run 1, ftz 1 are able to be activated by bicoid (bcd) throughout the anterior blastoderm and several lines of evidence indicate that they are repressed by the anterior gap genes slp1 (sloppy-paired 1), tll (tailless) and hkb (huckebein). The modest activity of these repressors led to the premise of a combinatorial mechanism regulating the expression of the CRMs of h 1, eve 1, run 1, ftz 1 in more anterior regions of the embryo. We tested this possibility by progressively removing the repression activities of slp1, tll and hkb. In doing so, we were able to expose a mechanism of additive repression limiting the anterior borders of stripes 1. Stripes 1 respond depending on their distance from the anterior end and repressors operating at different levels.
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Affiliation(s)
| | - Guilherme Miura Lavezzo
- Program on Bioinformatics, Institute of Mathematics and Statistics, University of São Paulo, São Paulo, Brazil
| | - Ariane Machado-Lima
- Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, São Paulo, SP, Brazil; Program on Bioinformatics, Institute of Mathematics and Statistics, University of São Paulo, São Paulo, Brazil
| | | | - Luiz Paulo Andrioli
- Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, São Paulo, SP, Brazil.
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23
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Shen J, Liu F, Tang C. Scaling dictates the decoder structure. Sci Bull (Beijing) 2022; 67:1486-1495. [PMID: 36546192 DOI: 10.1016/j.scib.2022.06.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 05/06/2022] [Accepted: 06/13/2022] [Indexed: 01/07/2023]
Abstract
Despite fluctuations in embryo size within a species, the spatial gene expression pattern and hence the embryonic structure can nonetheless maintain the correct proportion to the embryo size. This is known as the scaling phenomenon. For morphogen-induced patterning of gene expression, the positional information encoded in the local morphogen concentrations is decoded by the downstream genetic network (the decoder). In this paper, we show that the requirement of scaling sets severe constraints on the geometric structure of such a local decoder, which in turn enables deduction of mutants' behavior and extraction of regulation information without going into any molecular details. We demonstrate that the Drosophila gap gene system achieves scaling in the way consistent with our theory-the decoder geometry required by scaling correctly accounts for the observed gap gene expression pattern in nearly all maternal morphogen mutants. Furthermore, the regulation logic and the coding/decoding strategy of the gap gene system can also be revealed from the decoder geometry. Our work provides a general theoretical framework for a large class of problems where scaling output is achieved by non-scaling inputs and a local decoder, as well as a unified understanding of scaling, mutants' behavior, and gene regulation for the Drosophila gap gene system.
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Affiliation(s)
- Jingxiang Shen
- Center for Quantitative Biology, Peking University, Beijing 100871, China
| | - Feng Liu
- Center for Quantitative Biology, Peking University, Beijing 100871, China; School of Physics, Peking University, Beijing 100871, China
| | - Chao Tang
- Center for Quantitative Biology, Peking University, Beijing 100871, China; School of Physics, Peking University, Beijing 100871, China; Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China.
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24
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Akiyama-Oda Y, Akaiwa T, Oda H. Reconstruction of the Global Polarity of an Early Spider Embryo by Single-Cell and Single-Nucleus Transcriptome Analysis. Front Cell Dev Biol 2022; 10:933220. [PMID: 35938158 PMCID: PMC9353575 DOI: 10.3389/fcell.2022.933220] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 06/22/2022] [Indexed: 01/07/2023] Open
Abstract
Patterning along an axis of polarity is a fundamental step in the development of a multicellular animal embryo. In the cellular field of an early spider embryo, Hedgehog signaling operates to specify a “fuzzy” French-flag-like pattern along the primary axis, which is related to the future anterior–posterior (A–P) axis. However, details regarding the generation and development of a diversity of cell states based on the embryo polarity are not known. To address this issue, we applied single-cell RNA sequencing to the early spider embryo consisting of approximately 2,000 cells. Our results confirmed that this technique successfully detected 3 cell populations corresponding to the germ layers and some transient cell states. We showed that the data from dissociated cells had sufficient information for reconstruction of a correct global A–P polarity of the presumptive ectoderm, without clear segregation of specific cell states. This outcome is explained by the varied but differentially overlapping expression of Hedgehog-signal target genes and newly identified marker genes. We also showed that the data resources generated by the transcriptome analysis are applicable to a genome-wide search for genes whose expression is spatially regulated, based on the detection of pattern similarity. Furthermore, we performed single-nucleus RNA sequencing, which was more powerful in detecting emerging cell states. The single-cell and single-nucleus transcriptome techniques will help investigate the pattern-forming processes in the spider model system in an unbiased, comprehensive manner. We provided web-based resources of these transcriptome datasets for future studies of pattern formation and cell differentiation.
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Affiliation(s)
- Yasuko Akiyama-Oda
- JT Biohistory Research Hall, Takatsuki, Japan
- PRESTO, Japan Science and Technology Agency, Kawaguchi, Japan
- Department of Microbiology and Infection Control, Faculty of Medicine, Osaka Medical and Pharmaceutical University, Takatsuki, Japan
- *Correspondence: Yasuko Akiyama-Oda,
| | - Takanori Akaiwa
- JT Biohistory Research Hall, Takatsuki, Japan
- Department of Biological Science, Graduate School of Science, Osaka University, Toyonaka, Japan
| | - Hiroki Oda
- JT Biohistory Research Hall, Takatsuki, Japan
- Department of Biological Science, Graduate School of Science, Osaka University, Toyonaka, Japan
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25
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Brun-Usan M, Zimm R, Uller T. Beyond genotype-phenotype maps: Toward a phenotype-centered perspective on evolution. Bioessays 2022; 44:e2100225. [PMID: 35863907 DOI: 10.1002/bies.202100225] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 06/30/2022] [Accepted: 07/04/2022] [Indexed: 11/08/2022]
Abstract
Evolutionary biology is paying increasing attention to the mechanisms that enable phenotypic plasticity, evolvability, and extra-genetic inheritance. Yet, there is a concern that these phenomena remain insufficiently integrated within evolutionary theory. Understanding their evolutionary implications would require focusing on phenotypes and their variation, but this does not always fit well with the prevalent genetic representation of evolution that screens off developmental mechanisms. Here, we instead use development as a starting point, and represent it in a way that allows genetic, environmental and epigenetic sources of phenotypic variation to be independent. We show why this representation helps to understand the evolutionary consequences of both genetic and non-genetic phenotype determinants, and discuss how this approach can instigate future areas of empirical and theoretical research.
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Affiliation(s)
- Miguel Brun-Usan
- Department of Biology, Lund University, 22362, Lund, Sweden.,Institute for Life Sciences/Electronics and Computer Science, University of Southampton, SO17 1BJ, Southampton, UK
| | - Roland Zimm
- Ecole Normale Supérieure de Lyon, Institute de Génomique Fonctionnelle de Lyon, Lyon, France
| | - Tobias Uller
- Institute for Life Sciences/Electronics and Computer Science, University of Southampton, SO17 1BJ, Southampton, UK
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26
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Latent space of a small genetic network: Geometry of dynamics and information. Proc Natl Acad Sci U S A 2022; 119:e2113651119. [PMID: 35737842 PMCID: PMC9245618 DOI: 10.1073/pnas.2113651119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The high-dimensional character of most biological systems presents genuine challenges for modeling and prediction. Here we propose a neural network-based approach for dimensionality reduction and analysis of biological gene expression data, using, as a case study, a well-known genetic network in the early Drosophila embryo, the gap gene patterning system. We build an autoencoder compressing the dynamics of spatial gap gene expression into a two-dimensional (2D) latent map. The resulting 2D dynamics suggests an almost linear model, with a small bare set of essential interactions. Maternally defined spatial modes control gap genes positioning, without the classically assumed intricate set of repressive gap gene interactions. This, surprisingly, predicts minimal changes of neighboring gap domains when knocking out gap genes, consistent with previous observations. Latent space geometries in maternal mutants are also consistent with the existence of such spatial modes. Finally, we show how positional information is well defined and interpretable as a polar angle in latent space. Our work illustrates how optimization of small neural networks on medium-sized biological datasets is sufficiently informative to capture essential underlying mechanisms of network function.
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27
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Senthil Kumar S, Swaminathan A, Abdel-Daim MM, Sheik Mohideen S. A systematic review on the effects of acrylamide and bisphenol A on the development of Drosophila melanogaster. Mol Biol Rep 2022; 49:10703-10713. [PMID: 35753027 DOI: 10.1007/s11033-022-07642-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 03/14/2022] [Accepted: 05/25/2022] [Indexed: 11/28/2022]
Abstract
The current global scenario has instigated a steady upsurge of synthetic chemicals usage thereby creating a toxic environment unsuitable for animals and humans. Acrylamide and bisphenol A are some of the most common toxins found in the atmosphere due to their extensive involvement in numerous industrial processes. Acrylamide, an occupational hazard toxin has been known to cause severe nerve damage and peripheral neuronal damage in both animals and humans. General sources of acrylamide exposure are effluents from textile and paper industries, cosmetics, and thermally processed foods rich in starch. Bisphenol A (BPA) is generally found in food packaging materials, dental sealants, and plastic bottles. It is highly temperature-sensitive that can easily leach into the food products or humans on contact. The genotoxic and neurotoxic effects of acrylamide and bisphenol A have been widely researched; however, more attention should be dedicated to understanding the developmental toxicity of these chemicals. The developmental impacts of toxin exposure can be easily understood using Drosophila melanogaster as a model given considering its short life span and genetic homology to humans. In this review, we have discussed the toxic effects of acrylamide and BPA on the developmental process of Drosophila melanogaster.
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Affiliation(s)
- Swetha Senthil Kumar
- Developmental Biology Lab, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur - 603203, Chengalpattu District, Chengalpattu, Tamil Nadu, India
| | - Abhinaya Swaminathan
- Developmental Biology Lab, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur - 603203, Chengalpattu District, Chengalpattu, Tamil Nadu, India
| | - Mohamed M Abdel-Daim
- Pharmacology Department, Faculty of Veterinary Medicine, Suez Canal University, 41522, Ismailia, Egypt
| | - Sahabudeen Sheik Mohideen
- Developmental Biology Lab, Department of Biotechnology, School of Bioengineering, SRM Institute of Science and Technology, Kattankulathur - 603203, Chengalpattu District, Chengalpattu, Tamil Nadu, India.
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28
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Barbier I, Kusumawardhani H, Schaerli Y. Engineering synthetic spatial patterns in microbial populations and communities. Curr Opin Microbiol 2022; 67:102149. [DOI: 10.1016/j.mib.2022.102149] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 03/08/2022] [Accepted: 03/16/2022] [Indexed: 02/03/2023]
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29
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Iber D, Mederacke M. Tracheal Ring Formation. Front Cell Dev Biol 2022; 10:900447. [PMID: 35573681 PMCID: PMC9094403 DOI: 10.3389/fcell.2022.900447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Accepted: 04/05/2022] [Indexed: 12/02/2022] Open
Abstract
The trachea is a long tube that enables air passage between the larynx and the bronchi. C-shaped cartilage rings on the ventral side stabilise the structure. On its esophagus-facing dorsal side, deformable smooth muscle facilitates the passage of food in the esophagus. While the symmetry break along the dorsal-ventral axis is well understood, the molecular mechanism that results in the periodic Sox9 expression pattern that translates into the cartilage rings has remained elusive. Here, we review the molecular regulatory interactions that have been elucidated, and discuss possible patterning mechanisms. Understanding the principles of self-organisation is important, both to define biomedical interventions and to enable tissue engineering.
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Affiliation(s)
- Dagmar Iber
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
- Swiss Institute of Bioinformatics, Basel, Switzerland
- *Correspondence: Dagmar Iber,
| | - Malte Mederacke
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
- Swiss Institute of Bioinformatics, Basel, Switzerland
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30
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Fulton T, Verd B, Steventon B. The unappreciated generative role of cell movements in pattern formation. ROYAL SOCIETY OPEN SCIENCE 2022; 9:211293. [PMID: 35601454 PMCID: PMC9043703 DOI: 10.1098/rsos.211293] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 04/05/2022] [Indexed: 06/15/2023]
Abstract
The mechanisms underpinning the formation of patterned cellular landscapes has been the subject of extensive study as a fundamental problem of developmental biology. In most cases, attention has been given to situations in which cell movements are negligible, allowing researchers to focus on the cell-extrinsic signalling mechanisms, and intrinsic gene regulatory interactions that lead to pattern emergence at the tissue level. However, in many scenarios during development, cells rapidly change their neighbour relationships in order to drive tissue morphogenesis, while also undergoing patterning. To draw attention to the ubiquity of this problem and propose methodologies that will accommodate morphogenesis into the study of pattern formation, we review the current approaches to studying pattern formation in both static and motile cellular environments. We then consider how the cell movements themselves may contribute to the generation of pattern, rather than hinder it, with both a species specific and evolutionary viewpoint.
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Affiliation(s)
- Timothy Fulton
- Department of Genetics, University of Cambridge, Cambridge, UK
- School of Biological and Behavioural Sciences, Queen Mary University of London, London, UK
| | - Berta Verd
- Department of Genetics, University of Cambridge, Cambridge, UK
- Department of Zoology, University of Oxford, Oxford, UK
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31
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Singh AP, Wu P, Ryabichko S, Raimundo J, Swan M, Wieschaus E, Gregor T, Toettcher JE. Optogenetic control of the Bicoid morphogen reveals fast and slow modes of gap gene regulation. Cell Rep 2022; 38:110543. [PMID: 35320726 PMCID: PMC9019726 DOI: 10.1016/j.celrep.2022.110543] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Revised: 01/10/2022] [Accepted: 02/28/2022] [Indexed: 11/29/2022] Open
Abstract
Developmental patterning networks are regulated by multiple inputs and feedback connections that rapidly reshape gene expression, limiting the information that can be gained solely from slow genetic perturbations. Here we show that fast optogenetic stimuli, real-time transcriptional reporters, and a simplified genetic background can be combined to reveal the kinetics of gene expression downstream of a developmental transcription factor in vivo. We engineer light-controlled versions of the Bicoid transcription factor and study their effects on downstream gap genes in embryos. Our results recapitulate known relationships, including rapid Bicoid-dependent transcription of giant and hunchback and delayed repression of Krüppel. In addition, we find that the posterior pattern of knirps exhibits a quick but inverted response to Bicoid perturbation, suggesting a noncanonical role for Bicoid in directly suppressing knirps transcription. Acute modulation of transcription factor concentration while recording output gene activity represents a powerful approach for studying developmental gene networks in vivo.
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Affiliation(s)
- Anand P Singh
- Lewis Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Ping Wu
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Sergey Ryabichko
- Lewis Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - João Raimundo
- Lewis Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Michael Swan
- Lewis Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Eric Wieschaus
- Lewis Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
| | - Thomas Gregor
- Lewis Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Department of Physics, Princeton University, Princeton, NJ 08544, USA.
| | - Jared E Toettcher
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
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32
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Kamiyama T, Niwa R. Transcriptional Regulators of Ecdysteroid Biosynthetic Enzymes and Their Roles in Insect Development. Front Physiol 2022; 13:823418. [PMID: 35211033 PMCID: PMC8863297 DOI: 10.3389/fphys.2022.823418] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2021] [Accepted: 01/12/2022] [Indexed: 12/23/2022] Open
Abstract
Steroid hormones are responsible for coordinating many aspects of biological processes in most multicellular organisms, including insects. Ecdysteroid, the principal insect steroid hormone, is biosynthesized from dietary cholesterol or plant sterols. In the last 20 years, a number of ecdysteroidogenic enzymes, including Noppera-bo, Neverland, Shroud, Spook/Spookier, Cyp6t3, Phantom, Disembodied, Shadow, and Shade, have been identified and characterized in molecular genetic studies using the fruit fly Drosophila melanogaster. These enzymes are encoded by genes collectively called the Halloween genes. The transcriptional regulatory network, governed by multiple regulators of transcription, chromatin remodeling, and endoreplication, has been shown to be essential for the spatiotemporal expression control of Halloween genes in D. melanogaster. In this review, we summarize the latest information on transcriptional regulators that are crucial for controlling the expression of ecdysteroid biosynthetic enzymes and their roles in insect development.
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Affiliation(s)
- Takumi Kamiyama
- College of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
| | - Ryusuke Niwa
- Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tsukuba, Japan
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33
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Klein SL, Tavares ALP, Peterson M, Sullivan CH, Moody SA. Repressive Interactions Between Transcription Factors Separate Different Embryonic Ectodermal Domains. Front Cell Dev Biol 2022; 10:786052. [PMID: 35198557 PMCID: PMC8859430 DOI: 10.3389/fcell.2022.786052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 01/10/2022] [Indexed: 11/13/2022] Open
Abstract
The embryonic ectoderm is composed of four domains: neural plate, neural crest, pre-placodal region (PPR) and epidermis. Their formation is initiated during early gastrulation by dorsal-ventral and anterior-posterior gradients of signaling factors that first divide the embryonic ectoderm into neural and non-neural domains. Next, the neural crest and PPR domains arise, either via differential competence of the neural and non-neural ectoderm (binary competence model) or via interactions between the neural and non-neural ectoderm tissues to produce an intermediate neural border zone (NB) (border state model) that subsequently separates into neural crest and PPR. Many previous gain- and loss-of-function experiments demonstrate that numerous TFs are expressed in initially overlapping zones that gradually resolve into patterns that by late neurula stages are characteristic of each of the four domains. Several of these studies suggested that this is accomplished by a combination of repressive TF interactions and competence to respond to local signals. In this study, we ectopically expressed TFs that at neural plate stages are characteristic of one domain in a different domain to test whether they act cell autonomously as repressors. We found that almost all tested TFs caused reduced expression of the other TFs. At gastrulation these effects were strictly within the lineage-labeled cells, indicating that the effects were cell autonomous, i.e., due to TF interactions within individual cells. Analysis of previously published single cell RNAseq datasets showed that at the end of gastrulation, and continuing to neural tube closure stages, many ectodermal cells express TFs characteristic of more than one neural plate stage domain, indicating that different TFs have the opportunity to interact within the same cell. At neurula stages repression was observed both in the lineage-labeled cells and in adjacent cells not bearing detectable lineage label, suggesting that cell-to-cell signaling has begun to contribute to the separation of the domains. Together, these observations directly demonstrate previous suggestions in the literature that the segregation of embryonic ectodermal domains initially involves cell autonomous, repressive TF interactions within an individual cell followed by the subsequent advent of non-cell autonomous signaling to neighbors.
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Affiliation(s)
- Steven L Klein
- Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, D.C., DC, United States
| | - Andre L P Tavares
- Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, D.C., DC, United States
| | - Meredith Peterson
- Department of Biology, State College, Penn State University, University Park, PA, United States
| | | | - Sally A Moody
- Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, D.C., DC, United States
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34
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Abstract
Even if a species' phenotype does not change over evolutionary time, the underlying mechanism may change, as distinct molecular pathways can realize identical phenotypes. Here we use linear system theory to explore the consequences of this idea, describing how a gene network underlying a conserved phenotype evolves, as the genetic drift of small changes to these molecular pathways causes a population to explore the set of mechanisms with identical phenotypes. To do this, we model an organism's internal state as a linear system of differential equations for which the environment provides input and the phenotype is the output, in which context there exists an exact characterization of the set of all mechanisms that give the same input-output relationship. This characterization implies that selectively neutral directions in genotype space should be common and that the evolutionary exploration of these distinct but equivalent mechanisms can lead to the reproductive incompatibility of independently evolving populations. This evolutionary exploration, or system drift, is expected to proceed at a rate proportional to the amount of intrapopulation genetic variation divided by the effective population size ( Ne$N_e$ ). At biologically reasonable parameter values this could lead to substantial interpopulation incompatibility, and thus speciation, on a time scale of Ne$N_e$ generations. This model also naturally predicts Haldane's rule, thus providing a concrete explanation of why heterogametic hybrids tend to be disrupted more often than homogametes during the early stages of speciation.
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Affiliation(s)
- Joshua S. Schiffman
- New York Genome CenterNew YorkNew York 10013,Weill Cornell MedicineNew YorkNew York 10065,Department of Molecular and Computational BiologyUniversity of Southern CaliforniaLos AngelesCalifornia 90089
| | - Peter L. Ralph
- Department of Molecular and Computational BiologyUniversity of Southern CaliforniaLos AngelesCalifornia 90089,Department of Mathematics, Institute of Ecology and EvolutionUniversity of OregonEugeneOregon 97403,Department of Biology, Institute of Ecology and EvolutionUniversity of OregonEugeneOregon 97403
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35
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Trading bits in the readout from a genetic network. Proc Natl Acad Sci U S A 2021; 118:2109011118. [PMID: 34772813 DOI: 10.1073/pnas.2109011118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2021] [Indexed: 11/18/2022] Open
Abstract
In the regulation of gene expression, information of relevance to the organism is represented by the concentrations of transcription factor molecules. To extract this information the cell must effectively "measure" these concentrations, but there are physical limits to the precision of these measurements. We use the gap gene network in the early fly embryo as an example of the tradeoff between the precision of concentration measurements and the transmission of relevant information. For thresholded measurements we find that lower thresholds are more important, and fine tuning is not required for near-optimal information transmission. We then consider general sensors, constrained only by a limit on their information capacity, and find that thresholded sensors can approach true information theoretic optima. The information theoretic approach allows us to identify the optimal sensor for the entire gap gene network and to argue that the physical limitations of sensing necessitate the observed multiplicity of enhancer elements, with sensitivities to combinations rather than single transcription factors.
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36
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Duk MA, Gursky VV, Samsonova MG, Surkova SY. Application of Domain- and Genotype-Specific Models to Infer Post-Transcriptional Regulation of Segmentation Gene Expression in Drosophila. Life (Basel) 2021; 11:life11111232. [PMID: 34833107 PMCID: PMC8618293 DOI: 10.3390/life11111232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 11/05/2021] [Accepted: 11/10/2021] [Indexed: 11/16/2022] Open
Abstract
Unlike transcriptional regulation, the post-transcriptional mechanisms underlying zygotic segmentation gene expression in early Drosophila embryo have been insufficiently investigated. Condition-specific post-transcriptional regulation plays an important role in the development of many organisms. Our recent study revealed the domain- and genotype-specific differences between mRNA and the protein expression of Drosophila hb, gt, and eve genes in cleavage cycle 14A. Here, we use this dataset and the dynamic mathematical model to recapitulate protein expression from the corresponding mRNA patterns. The condition-specific nonuniformity in parameter values is further interpreted in terms of possible post-transcriptional modifications. For hb expression in wild-type embryos, our results predict the position-specific differences in protein production. The protein synthesis rate parameter is significantly higher in hb anterior domain compared to the posterior domain. The parameter sets describing Gt protein dynamics in wild-type embryos and Kr mutants are genotype-specific. The spatial discrepancy between gt mRNA and protein posterior expression in Kr mutants is well reproduced by the whole axis model, thus rejecting the involvement of post-transcriptional mechanisms. Our models fail to describe the full dynamics of eve expression, presumably due to its complex shape and the variable time delays between mRNA and protein patterns, which likely require a more complex model. Overall, our modeling approach enables the prediction of regulatory scenarios underlying the condition-specific differences between mRNA and protein expression in early embryo.
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Affiliation(s)
- Maria A. Duk
- Mathematical Biology and Bioinformatics Laboratory, Peter the Great Saint Petersburg Polytechnic University, 195251 St. Petersburg, Russia; (M.A.D.); (M.G.S.)
- Theoretical Department, Ioffe Institute, 194021 St. Petersburg, Russia;
| | - Vitaly V. Gursky
- Theoretical Department, Ioffe Institute, 194021 St. Petersburg, Russia;
| | - Maria G. Samsonova
- Mathematical Biology and Bioinformatics Laboratory, Peter the Great Saint Petersburg Polytechnic University, 195251 St. Petersburg, Russia; (M.A.D.); (M.G.S.)
| | - Svetlana Yu. Surkova
- Mathematical Biology and Bioinformatics Laboratory, Peter the Great Saint Petersburg Polytechnic University, 195251 St. Petersburg, Russia; (M.A.D.); (M.G.S.)
- Correspondence:
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37
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Chevin LM, Leung C, Le Rouzic A, Uller T. Using phenotypic plasticity to understand the structure and evolution of the genotype-phenotype map. Genetica 2021; 150:209-221. [PMID: 34617196 DOI: 10.1007/s10709-021-00135-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 09/22/2021] [Indexed: 10/20/2022]
Abstract
Deciphering the genotype-phenotype map necessitates relating variation at the genetic level to variation at the phenotypic level. This endeavour is inherently limited by the availability of standing genetic variation, the rate of spontaneous mutation to novo genetic variants, and possible biases associated with induced mutagenesis. An interesting alternative is to instead rely on the environment as a source of variation. Many phenotypic traits change plastically in response to the environment, and these changes are generally underlain by changes in gene expression. Relating gene expression plasticity to the phenotypic plasticity of more integrated organismal traits thus provides useful information about which genes influence the development and expression of which traits, even in the absence of genetic variation. We here appraise the prospects and limits of such an environment-for-gene substitution for investigating the genotype-phenotype map. We review models of gene regulatory networks, and discuss the different ways in which they can incorporate the environment to mechanistically model phenotypic plasticity and its evolution. We suggest that substantial progress can be made in deciphering this genotype-environment-phenotype map, by connecting theory on gene regulatory network to empirical patterns of gene co-expression, and by more explicitly relating gene expression to the expression and development of phenotypes, both theoretically and empirically.
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Affiliation(s)
- Luis-Miguel Chevin
- CEFE, Univ Montpellier, CNRS, EPHE, IRD, Univ Paul Valéry Montpellier 3, Montpellier, France.
| | - Christelle Leung
- CEFE, Univ Montpellier, CNRS, EPHE, IRD, Univ Paul Valéry Montpellier 3, Montpellier, France
| | - Arnaud Le Rouzic
- Laboratoire Évolution, Génomes, Comportement, Écologie, CNRS, IRD, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Tobias Uller
- Department of Biology, Lund University, Lund, Sweden
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38
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Diaz-Cuadros M, Pourquié O, El-Sherif E. Patterning with clocks and genetic cascades: Segmentation and regionalization of vertebrate versus insect body plans. PLoS Genet 2021; 17:e1009812. [PMID: 34648490 PMCID: PMC8516289 DOI: 10.1371/journal.pgen.1009812] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Oscillatory and sequential processes have been implicated in the spatial patterning of many embryonic tissues. For example, molecular clocks delimit segmental boundaries in vertebrates and insects and mediate lateral root formation in plants, whereas sequential gene activities are involved in the specification of regional identities of insect neuroblasts, vertebrate neural tube, vertebrate limb, and insect and vertebrate body axes. These processes take place in various tissues and organisms, and, hence, raise the question of what common themes and strategies they share. In this article, we review 2 processes that rely on the spatial regulation of periodic and sequential gene activities: segmentation and regionalization of the anterior-posterior (AP) axis of animal body plans. We study these processes in species that belong to 2 different phyla: vertebrates and insects. By contrasting 2 different processes (segmentation and regionalization) in species that belong to 2 distantly related phyla (arthropods and vertebrates), we elucidate the deep logic of patterning by oscillatory and sequential gene activities. Furthermore, in some of these organisms (e.g., the fruit fly Drosophila), a mode of AP patterning has evolved that seems not to overtly rely on oscillations or sequential gene activities, providing an opportunity to study the evolution of pattern formation mechanisms.
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Affiliation(s)
- Margarete Diaz-Cuadros
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Pathology, Brigham and Women’s Hospital, Boston, Massachusetts, United States of America
| | - Olivier Pourquié
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Pathology, Brigham and Women’s Hospital, Boston, Massachusetts, United States of America
- Harvard Stem Cell Institute, Harvard University, Cambridge, Massachusetts, United States of America
| | - Ezzat El-Sherif
- Division of Developmental Biology, Department of Biology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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39
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Waymack R, Gad M, Wunderlich Z. Molecular competition can shape enhancer activity in the Drosophila embryo. iScience 2021; 24:103034. [PMID: 34568782 PMCID: PMC8449247 DOI: 10.1016/j.isci.2021.103034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 07/27/2021] [Accepted: 08/20/2021] [Indexed: 01/12/2023] Open
Abstract
Transgenic reporters allow the measurement of regulatory DNA activity in vivo and consequently have long been useful tools for studying enhancers. Despite their utility, few studies have investigated the effects these reporters may have on the expression of other genes. Understanding these effects is required to accurately interpret reporter data and characterize gene regulatory mechanisms. By measuring the expression of Kruppel (Kr) enhancer reporters in live Drosophila embryos, we find reporters inhibit one another’s expression and that of a nearby endogenous gene. Using synthetic transcription factor (TF) binding site arrays, we present evidence that competition for TFs is partially responsible for the observed transcriptional inhibition. We develop a simple thermodynamic model that predicts competition of the measured magnitude specifically when TF binding is restricted to distinct nuclear subregions. Our findings underline an unexpected role of the non-homogenous nature of the nucleus in regulating gene expression. Live tracking of transcription reveals competition between transgenic reporters Transgenic reporters can also depress the expression of a neighboring gene Expression inhibition is in part because of competition for transcription factors (TFs) Competition is predicted with a model that restricts TFs to sub-nuclear “hubs”
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Affiliation(s)
- Rachel Waymack
- Department of Developmental and Cell Biology, University of California, Irvine, CA 92697, USA
| | - Mario Gad
- Department of Developmental and Cell Biology, University of California, Irvine, CA 92697, USA
| | - Zeba Wunderlich
- Department of Developmental and Cell Biology, University of California, Irvine, CA 92697, USA.,Department of Biology, Boston University, 610 Commonwealth Ave., Boston, MA 02215, USA.,Biological Design Center, Boston University, 610 Commonwealth Avenue, Boston, MA 02215, USA
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40
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Chipman AD. The evolution of the gene regulatory networks patterning the Drosophila Blastoderm. Curr Top Dev Biol 2021; 139:297-324. [PMID: 32450964 DOI: 10.1016/bs.ctdb.2020.02.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The Drosophila blastoderm gene regulatory network is one of the best studied networks in biology. It is composed of a series of tiered sub-networks that act sequentially to generate a primary segmental pattern. Many of these sub-networks have been studied in other arthropods, allowing us to reconstruct how each of them evolved over the transition from the arthropod ancestor to the situation seen in Drosophila today. I trace the evolution of each of these networks, showing how some of them have been modified significantly in Drosophila relative to the ancestral state while others are largely conserved across evolutionary timescales. I compare the putative ancestral arthropod segmentation network with that found in Drosophila and discuss how and why it has been modified throughout evolution, and to what extent this modification is unusual.
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Affiliation(s)
- Ariel D Chipman
- The Department of Ecology, Evolution & Behavior, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem, Israel.
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41
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Garbuzov FE, Gursky VV. Nonequilibrium model of short-range repression in gene transcription regulation. Phys Rev E 2021; 104:014407. [PMID: 34412298 DOI: 10.1103/physreve.104.014407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 06/24/2021] [Indexed: 11/07/2022]
Abstract
Transcription factors are proteins that regulate gene activity by activating or repressing gene transcription. A special class of transcriptional repressors operates via a short-range mechanism, making local DNA regions inaccessible to binding by activators, and thus providing an indirect repressive action on the target gene. This mechanism is commonly modeled assuming that repressors interact with DNA under thermodynamic equilibrium and neglecting some configurations of the gene regulatory region. We elaborate on a more general nonequilibrium model of short-range repression using the graph formalism for transitions between gene states, and we apply analytical calculations to compare it with the equilibrium model in terms of the repression strength and expression noise. In contrast to the equilibrium approach, the new model allows us to separate two basic mechanisms of short-range repression. The first mechanism is associated with the recruiting of factors that mediate chromatin condensation, and the second one concerns the blocking of factors that mediate chromatin loosening. The nonequilibrium model demonstrates better performance on previously published gene expression data obtained for transcription factors controlling Drosophila development, and furthermore it predicts that the first repression mechanism is the most favorable in this system. The presented approach can be scaled to larger gene networks and can be used to infer specific modes and parameters of transcriptional regulation from gene expression data.
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Affiliation(s)
- F E Garbuzov
- Ioffe Institute, 26 Polytekhnicheskaya, St. Petersburg 194021, Russia
| | - V V Gursky
- Ioffe Institute, 26 Polytekhnicheskaya, St. Petersburg 194021, Russia
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42
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Tidswell ORA, Benton MA, Akam M. The neuroblast timer gene nubbin exhibits functional redundancy with gap genes to regulate segment identity in Tribolium. Development 2021; 148:271199. [PMID: 34351412 PMCID: PMC8406537 DOI: 10.1242/dev.199719] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 07/23/2021] [Indexed: 12/05/2022]
Abstract
The neuroblast timer genes hunchback, Krüppel, nubbin and castor are expressed in temporal sequence in neural stem cells, and in corresponding spatial sequence along the Drosophila blastoderm. As canonical gap genes, hunchback and Krüppel play a crucial role in insect segmentation, but the roles of nubbin and castor in this process remain ambiguous. We have investigated the expression and functions of nubbin and castor during segmentation in the beetle Tribolium. We show that Tc-hunchback, Tc-Krüppel, Tc-nubbin and Tc-castor are expressed sequentially in the segment addition zone, and that Tc-nubbin regulates segment identity redundantly with two previously described gap/gap-like genes, Tc-giant and Tc-knirps. Simultaneous knockdown of Tc-nubbin, Tc-giant and Tc-knirps results in the formation of ectopic legs on abdominal segments. This homeotic transformation is caused by loss of abdominal Hox gene expression, likely due to expanded Tc-Krüppel expression. Our findings support the theory that the neuroblast timer series was co-opted for use in insect segment patterning, and contribute to our growing understanding of the evolution and function of the gap gene network outside of Drosophila. Summary:nubbin and the gap genes knirps and giant redundantly repress Krüppel expression during segmentation. Simultaneous knockdown of all three genes causes ectopic Krüppel expression and loss of abdominal segment identity.
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Affiliation(s)
| | - Matthew A Benton
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK
| | - Michael Akam
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK
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43
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Cai X, Rondeel I, Baumgartner S. Modulating the bicoid gradient in space and time. Hereditas 2021; 158:29. [PMID: 34404481 PMCID: PMC8371787 DOI: 10.1186/s41065-021-00192-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 07/19/2021] [Indexed: 11/15/2022] Open
Abstract
Background The formation of the Bicoid (Bcd) gradient in the early Drosophila is one of the most fascinating observations in biology and serves as a paradigm for gradient formation, yet its mechanism is still not fully understood. Two distinct models were proposed in the past, the SDD and the ARTS model. Results We define novel cis- and trans-acting factors that are indispensable for gradient formation. The first one is the poly A tail length of the bcd mRNA where we demonstrate that it changes not only in time, but also in space. We show that posterior bcd mRNAs possess a longer poly tail than anterior ones and this elongation is likely mediated by wispy (wisp), a poly A polymerase. Consequently, modulating the activity of Wisp results in changes of the Bcd gradient, in controlling downstream targets such as the gap and pair-rule genes, and also in influencing the cuticular pattern. Attempts to modulate the Bcd gradient by subjecting the egg to an extra nuclear cycle, i.e. a 15th nuclear cycle by means of the maternal haploid (mh) mutation showed no effect, neither on the appearance of the gradient nor on the control of downstream target. This suggests that the segmental anlagen are determined during the first 14 nuclear cycles. Finally, we identify the Cyclin B (CycB) gene as a trans-acting factor that modulates the movement of Bcd such that Bcd movement is allowed to move through the interior of the egg. Conclusions Our analysis demonstrates that Bcd gradient formation is far more complex than previously thought requiring a revision of the models of how the gradient is formed.
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Affiliation(s)
- Xiaoli Cai
- Departmentof Experimental Medical Sciences, Lund University, BMC D10, 22184, Lund, Sweden
| | - Inge Rondeel
- Departmentof Experimental Medical Sciences, Lund University, BMC D10, 22184, Lund, Sweden.,Present address: Hubrecht Institute, 3584 CT, Utrecht, The Netherlands
| | - Stefan Baumgartner
- Departmentof Experimental Medical Sciences, Lund University, BMC D10, 22184, Lund, Sweden. .,Department of Biology, University of Konstanz, 78457, Konstanz, Germany.
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44
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The early Drosophila embryo as a model system for quantitative biology. Cells Dev 2021; 168:203722. [PMID: 34298230 DOI: 10.1016/j.cdev.2021.203722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Revised: 06/03/2021] [Accepted: 07/13/2021] [Indexed: 11/20/2022]
Abstract
With the rise of new tools, from controlled genetic manipulations and optogenetics to improved microscopy, it is now possible to make clear, quantitative and reproducible measurements of biological processes. The humble fruit fly Drosophila melanogaster, with its ease of genetic manipulation combined with excellent imaging accessibility, has become a major model system for performing quantitative in vivo measurements. Such measurements are driving a new wave of interest from physicists and engineers, who are developing a range of testable dynamic models of active systems to understand fundamental biological processes. The reproducibility of the early Drosophila embryo has been crucial for understanding how biological systems are robust to unavoidable noise during development. Insights from quantitative in vivo experiments in the Drosophila embryo are having an impact on our understanding of critical biological processes, such as how cells make decisions and how complex tissue shape emerges. Here, to highlight the power of using Drosophila embryogenesis for quantitative biology, I focus on three main areas: (1) formation and robustness of morphogen gradients; (2) how gene regulatory networks ensure precise boundary formation; and (3) how mechanical interactions drive packing and tissue folding. I further discuss how such data has driven advances in modelling.
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45
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Abstract
Arthropod segmentation and vertebrate somitogenesis are leading fields in the experimental and theoretical interrogation of developmental patterning. However, despite the sophistication of current research, basic conceptual issues remain unresolved. These include: (i) the mechanistic origins of spatial organization within the segment addition zone (SAZ); (ii) the mechanistic origins of segment polarization; (iii) the mechanistic origins of axial variation; and (iv) the evolutionary origins of simultaneous patterning. Here, I explore these problems using coarse-grained models of cross-regulating dynamical processes. In the morphogenetic framework of a row of cells undergoing axial elongation, I simulate interactions between an 'oscillator', a 'switch' and up to three 'timers', successfully reproducing essential patterning behaviours of segmenting systems. By comparing the output of these largely cell-autonomous models to variants that incorporate positional information, I find that scaling relationships, wave patterns and patterning dynamics all depend on whether the SAZ is regulated by temporal or spatial information. I also identify three mechanisms for polarizing oscillator output, all of which functionally implicate the oscillator frequency profile. Finally, I demonstrate significant dynamical and regulatory continuity between sequential and simultaneous modes of segmentation. I discuss these results in the context of the experimental literature.
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Affiliation(s)
- Erik Clark
- Department of Systems Biology, Harvard Medical School, 210 Longwood Ave, Boston, MA 02115, USA
- Trinity College Cambridge, University of Cambridge, Trinity Street, Cambridge CB2 1TQ, UK
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46
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Perkins ML. Implications of diffusion and time-varying morphogen gradients for the dynamic positioning and precision of bistable gene expression boundaries. PLoS Comput Biol 2021; 17:e1008589. [PMID: 34061823 PMCID: PMC8195430 DOI: 10.1371/journal.pcbi.1008589] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Revised: 06/11/2021] [Accepted: 05/11/2021] [Indexed: 11/19/2022] Open
Abstract
The earliest models for how morphogen gradients guide embryonic patterning failed to account for experimental observations of temporal refinement in gene expression domains. Following theoretical and experimental work in this area, dynamic positional information has emerged as a conceptual framework to discuss how cells process spatiotemporal inputs into downstream patterns. Here, we show that diffusion determines the mathematical means by which bistable gene expression boundaries shift over time, and therefore how cells interpret positional information conferred from morphogen concentration. First, we introduce a metric for assessing reproducibility in boundary placement or precision in systems where gene products do not diffuse, but where morphogen concentrations are permitted to change in time. We show that the dynamics of the gradient affect the sensitivity of the final pattern to variation in initial conditions, with slower gradients reducing the sensitivity. Second, we allow gene products to diffuse and consider gene expression boundaries as propagating wavefronts with velocity modulated by local morphogen concentration. We harness this perspective to approximate a PDE model as an ODE that captures the position of the boundary in time, and demonstrate the approach with a preexisting model for Hunchback patterning in fruit fly embryos. We then propose a design that employs antiparallel morphogen gradients to achieve accurate boundary placement that is robust to scaling. Throughout our work we draw attention to tradeoffs among initial conditions, boundary positioning, and the relative timescales of network and gradient evolution. We conclude by suggesting that mathematical theory should serve to clarify not just our quantitative, but also our intuitive understanding of patterning processes.
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Affiliation(s)
- Melinda Liu Perkins
- Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
- * E-mail:
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47
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Shen J, Liu F, Tu Y, Tang C. Finding gene network topologies for given biological function with recurrent neural network. Nat Commun 2021; 12:3125. [PMID: 34035278 PMCID: PMC8149884 DOI: 10.1038/s41467-021-23420-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 04/28/2021] [Indexed: 11/12/2022] Open
Abstract
Searching for possible biochemical networks that perform a certain function is a challenge in systems biology. For simple functions and small networks, this can be achieved through an exhaustive search of the network topology space. However, it is difficult to scale this approach up to larger networks and more complex functions. Here we tackle this problem by training a recurrent neural network (RNN) to perform the desired function. By developing a systematic perturbative method to interrogate the successfully trained RNNs, we are able to distill the underlying regulatory network among the biological elements (genes, proteins, etc.). Furthermore, we show several cases where the regulation networks found by RNN can achieve the desired biological function when its edges are expressed by more realistic response functions, such as the Hill-function. This method can be used to link topology and function by helping uncover the regulation logic and network topology for complex tasks. Networks are useful ways to describe interactions between molecules in a cell, but predicting the real topology of large networks can be challenging. Here, the authors use deep learning to predict the topology of networks that perform biologically-plausible functions.
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Affiliation(s)
- Jingxiang Shen
- Center for Quantitative Biology, Peking University, Beijing, China.,School of Physics, Peking University, Beijing, China
| | - Feng Liu
- Center for Quantitative Biology, Peking University, Beijing, China.,School of Physics, Peking University, Beijing, China
| | - Yuhai Tu
- IBM T. J. Watson Research Center, Yorktown Heights, New York, USA
| | - Chao Tang
- Center for Quantitative Biology, Peking University, Beijing, China. .,School of Physics, Peking University, Beijing, China. .,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China.
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48
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Fukaya T. Dynamic regulation of anterior-posterior patterning genes in living Drosophila embryos. Curr Biol 2021; 31:2227-2236.e6. [PMID: 33761316 DOI: 10.1016/j.cub.2021.02.050] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 01/27/2021] [Accepted: 02/18/2021] [Indexed: 10/21/2022]
Abstract
Expression of the gap and pair-rule genes plays an essential role in body segmentation during Drosophila embryogenesis.1-5 However, it remains unclear how precise expression patterns of these key developmental genes arise from stochastic transcriptional activation at the single-cell level. Here, I employed genome-editing and live-imaging approaches to comprehensively visualize regulation of the gap and pair-rule genes at the endogenous loci. Quantitative image analysis revealed that the total duration of active transcription (transcription period) is a major determinant of spatial patterning of gene expression in early embryos. The length of the transcription period is determined by the continuity of bursting activities in individual nuclei, with the core expression domain producing more bursts than boundary regions. Each gene exhibits a distinct rate of nascent RNA production during transcriptional bursting, which contributes to gene-to-gene variability in the total output. I also provide evidence for "enhancer interference," wherein a distal weak enhancer interferes with transcriptional activation by a strong proximal enhancer to downregulate the length of the transcription period without changing the transcription rate. Analysis of the endogenous hunchback (hb) locus revealed that the removal of the distal shadow enhancer induces strong ectopic transcriptional activation, which suppresses refinement of the initial broad expression domain into narrower stripe patterns at the anterior part of embryos. This study provides key insights into the link between transcriptional bursting, enhancer-promoter interaction, and spatiotemporal patterning of gene expression during animal development.
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Affiliation(s)
- Takashi Fukaya
- Laboratory of Transcription Dynamics, Research Center for Biological Visualization, Institute for Quantitative Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan; Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
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49
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Zhu M, Zernicka-Goetz M. Principles of Self-Organization of the Mammalian Embryo. Cell 2021; 183:1467-1478. [PMID: 33306953 DOI: 10.1016/j.cell.2020.11.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 10/23/2020] [Accepted: 11/02/2020] [Indexed: 02/07/2023]
Abstract
Early embryogenesis is a conserved and self-organized process. In the mammalian embryo, the potential for self-organization is manifested in its extraordinary developmental plasticity, allowing a correctly patterned embryo to arise despite experimental perturbation. The underlying mechanisms enabling such regulative development have long been a topic of study. In this Review, we summarize our current understanding of the self-organizing principles behind the regulative nature of the early mammalian embryo. We argue that geometrical constraints, feedback between mechanical and biochemical factors, and cellular heterogeneity are all required to ensure the developmental plasticity of mammalian embryo development.
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Affiliation(s)
- Meng Zhu
- Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK; Present address: Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA.
| | - Magdalena Zernicka-Goetz
- Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK; Division of Biology and Biological Engineering, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA.
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50
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Morales JS, Raspopovic J, Marcon L. From embryos to embryoids: How external signals and self-organization drive embryonic development. Stem Cell Reports 2021; 16:1039-1050. [PMID: 33979592 PMCID: PMC8185431 DOI: 10.1016/j.stemcr.2021.03.026] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 03/19/2021] [Accepted: 03/22/2021] [Indexed: 12/15/2022] Open
Abstract
Embryonic development has been traditionally seen as an inductive process directed by exogenous maternal inputs and extra-embryonic signals. Increasing evidence, however, is showing that, in addition to exogenous signals, the development of the embryo involves endogenous self-organization. Recently, this self-organizing potential has been highlighted by a number of stem cell models known as embryoids that can recapitulate different aspects of embryogenesis in vitro. Here, we review the self-organizing behaviors observed in different embryoid models and seek to reconcile this new evidence with classical knowledge of developmental biology. This analysis leads to reexamine embryonic development as a guided self-organizing process, where patterning and morphogenesis are controlled by a combination of exogenous signals and endogenous self-organization. Finally, we discuss the multidisciplinary approach required to investigate the genetic and cellular basis of self-organization.
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Affiliation(s)
- J Serrano Morales
- Andalusian Center for Developmental Biology (CABD), CSIC - UPO - JA, Seville, Spain
| | - Jelena Raspopovic
- Andalusian Center for Developmental Biology (CABD), CSIC - UPO - JA, Seville, Spain.
| | - Luciano Marcon
- Andalusian Center for Developmental Biology (CABD), CSIC - UPO - JA, Seville, Spain.
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