1
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Ramesh PS, Chu LF. Species-specific roles of the Notch ligands, receptors, and targets orchestrating the signaling landscape of the segmentation clock. Front Cell Dev Biol 2024; 11:1327227. [PMID: 38348091 PMCID: PMC10859470 DOI: 10.3389/fcell.2023.1327227] [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: 10/24/2023] [Accepted: 12/20/2023] [Indexed: 02/15/2024] Open
Abstract
Somitogenesis is a hallmark feature of all vertebrates and some invertebrate species that involves the periodic formation of block-like structures called somites. Somites are transient embryonic segments that eventually establish the entire vertebral column. A highly conserved molecular oscillator called the segmentation clock underlies this periodic event and the pace of this clock regulates the pace of somite formation. Although conserved signaling pathways govern the clock in most vertebrates, the mechanisms underlying the species-specific divergence in various clock characteristics remain elusive. For example, the segmentation clock in classical model species such as zebrafish, chick, and mouse embryos tick with a periodicity of ∼30, ∼90, and ∼120 min respectively. This enables them to form the species-specific number of vertebrae during their overall timespan of somitogenesis. Here, we perform a systematic review of the species-specific features of the segmentation clock with a keen focus on mouse embryos. We perform this review using three different perspectives: Notch-responsive clock genes, ligand-receptor dynamics, and synchronization between neighboring oscillators. We further review reports that use non-classical model organisms and in vitro model systems that complement our current understanding of the segmentation clock. Our review highlights the importance of comparative developmental biology to further our understanding of this essential developmental process.
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Affiliation(s)
- Pranav S. Ramesh
- Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada
- Reproductive Biology and Regenerative Medicine Research Group, University of Calgary, Calgary, AB, Canada
- Alberta Children’s Hospital Research Institute, Calgary, AB, Canada
| | - Li-Fang Chu
- Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada
- Reproductive Biology and Regenerative Medicine Research Group, University of Calgary, Calgary, AB, Canada
- Alberta Children’s Hospital Research Institute, Calgary, AB, Canada
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2
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Loureiro C, Venzin OF, Oates AC. Generation of patterns in the paraxial mesoderm. Curr Top Dev Biol 2023; 159:372-405. [PMID: 38729682 DOI: 10.1016/bs.ctdb.2023.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2024]
Abstract
The Segmentation Clock is a tissue-level patterning system that enables the segmentation of the vertebral column precursors into transient multicellular blocks called somites. This patterning system comprises a set of elements that are essential for correct segmentation. Under the so-called "Clock and Wavefront" model, the system consists of two elements, a genetic oscillator that manifests itself as traveling waves of gene expression, and a regressing wavefront that transforms the temporally periodic signal encoded in the oscillations into a permanent spatially periodic pattern of somite boundaries. Over the last twenty years, every new discovery about the Segmentation Clock has been tightly linked to the nomenclature of the "Clock and Wavefront" model. This constrained allocation of discoveries into these two elements has generated long-standing debates in the field as what defines molecularly the wavefront and how and where the interaction between the two elements establishes the future somite boundaries. In this review, we propose an expansion of the "Clock and Wavefront" model into three elements, "Clock", "Wavefront" and signaling gradients. We first provide a detailed description of the components and regulatory mechanisms of each element, and we then examine how the spatiotemporal integration of the three elements leads to the establishment of the presumptive somite boundaries. To be as exhaustive as possible, we focus on the Segmentation Clock in zebrafish. Furthermore, we show how this three-element expansion of the model provides a better understanding of the somite formation process and we emphasize where our current understanding of this patterning system remains obscure.
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Affiliation(s)
- Cristina Loureiro
- Institute of Bioengineering, School of Life Sciences, Swiss Federal Institute of Technology Lausanne EPFL, Switzerland
| | - Olivier F Venzin
- Institute of Bioengineering, School of Life Sciences, Swiss Federal Institute of Technology Lausanne EPFL, Switzerland
| | - Andrew C Oates
- Institute of Bioengineering, School of Life Sciences, Swiss Federal Institute of Technology Lausanne EPFL, Switzerland.
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3
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Keseroglu K, Zinani OQH, Keskin S, Seawall H, Alpay EE, Özbudak EM. Stochastic gene expression and environmental stressors trigger variable somite segmentation phenotypes. Nat Commun 2023; 14:6497. [PMID: 37838784 PMCID: PMC10576776 DOI: 10.1038/s41467-023-42220-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 10/04/2023] [Indexed: 10/16/2023] Open
Abstract
Mutations of several genes cause incomplete penetrance and variable expressivity of phenotypes, which are usually attributed to modifier genes or gene-environment interactions. Here, we show stochastic gene expression underlies the variability of somite segmentation defects in embryos mutant for segmentation clock genes her1 or her7. Phenotypic strength is further augmented by low temperature and hypoxia. By performing live imaging of the segmentation clock reporters, we further show that groups of cells with higher oscillation amplitudes successfully form somites while those with lower amplitudes fail to do so. In unfavorable environments, the number of cycles with high amplitude oscillations and the number of successful segmentations proportionally decrease. These results suggest that individual oscillation cycles stochastically fail to pass a threshold amplitude, resulting in segmentation defects in mutants. Our quantitative methodology is adaptable to investigate variable phenotypes of mutant genes in different tissues.
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Affiliation(s)
- Kemal Keseroglu
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Oriana Q H Zinani
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
- Molecular and Developmental Biology Graduate Program, University of Cincinnati, College of Medicine, Cincinnati, OH, 45229, USA
| | - Sevdenur Keskin
- Allergy and Immunology, University of Arkansas for Medical Science and Arkansas Children's Hospital, Little Rock, AR, 72202, USA
| | - Hannah Seawall
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Eslim E Alpay
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Ertuğrul M Özbudak
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA.
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, 45229, USA.
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4
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Peng C, Wu DD, Ren JL, Peng ZL, Ma Z, Wu W, Lv Y, Wang Z, Deng C, Jiang K, Parkinson CL, Qi Y, Zhang ZY, Li JT. Large-scale snake genome analyses provide insights into vertebrate development. Cell 2023; 186:2959-2976.e22. [PMID: 37339633 DOI: 10.1016/j.cell.2023.05.030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 04/06/2023] [Accepted: 05/19/2023] [Indexed: 06/22/2023]
Abstract
Snakes are a remarkable squamate lineage with unique morphological adaptations, especially those related to the evolution of vertebrate skeletons, organs, and sensory systems. To clarify the genetic underpinnings of snake phenotypes, we assembled and analyzed 14 de novo genomes from 12 snake families. We also investigated the genetic basis of the morphological characteristics of snakes using functional experiments. We identified genes, regulatory elements, and structural variations that have potentially contributed to the evolution of limb loss, an elongated body plan, asymmetrical lungs, sensory systems, and digestive adaptations in snakes. We identified some of the genes and regulatory elements that might have shaped the evolution of vision, the skeletal system and diet in blind snakes, and thermoreception in infrared-sensitive snakes. Our study provides insights into the evolution and development of snakes and vertebrates.
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Affiliation(s)
- Changjun Peng
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Dong-Dong Wu
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
| | - Jin-Long Ren
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China
| | - Zhong-Liang Peng
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhifei Ma
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wei Wu
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yunyun Lv
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; College of Life Science, Neijiang Normal University, Neijiang, Sichuan 641100, China
| | - Zeng Wang
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Cao Deng
- Departments of Bioinformatics, DNA Stories Bioinformatics Center, Chengdu 610000, China
| | - Ke Jiang
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China
| | | | - Yin Qi
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China
| | - Zhi-Yi Zhang
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China
| | - Jia-Tang Li
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610040, China; University of Chinese Academy of Sciences, Beijing 100049, China; Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences, Yezin, Nay Pyi Taw 05282, Myanmar.
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5
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Blatnik MC, Gallagher TL, Amacher SL. Keeping development on time: Insights into post-transcriptional mechanisms driving oscillatory gene expression during vertebrate segmentation. WILEY INTERDISCIPLINARY REVIEWS. RNA 2023; 14:e1751. [PMID: 35851751 PMCID: PMC9840655 DOI: 10.1002/wrna.1751] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 06/13/2022] [Accepted: 06/20/2022] [Indexed: 01/31/2023]
Abstract
Biological time keeping, or the duration and tempo at which biological processes occur, is a phenomenon that drives dynamic molecular and morphological changes that manifest throughout many facets of life. In some cases, the molecular mechanisms regulating the timing of biological transitions are driven by genetic oscillations, or periodic increases and decreases in expression of genes described collectively as a "molecular clock." In vertebrate animals, molecular clocks play a crucial role in fundamental patterning and cell differentiation processes throughout development. For example, during early vertebrate embryogenesis, the segmentation clock regulates the patterning of the embryonic mesoderm into segmented blocks of tissue called somites, which later give rise to axial skeletal muscle and vertebrae. Segmentation clock oscillations are characterized by rapid cycles of mRNA and protein expression. For segmentation clock oscillations to persist, the transcript and protein molecules of clock genes must be short-lived. Faithful, rhythmic, genetic oscillations are sustained by precise regulation at many levels, including post-transcriptional regulation, and such mechanisms are essential for proper vertebrate development. This article is categorized under: RNA Export and Localization > RNA Localization RNA Turnover and Surveillance > Regulation of RNA Stability Translation > Regulation.
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Affiliation(s)
- Monica C. Blatnik
- The Ohio State University, Department of Molecular Genetics, Columbus, Ohio, 43210-1132, United States
| | - Thomas L. Gallagher
- The Ohio State University, Department of Molecular Genetics, Columbus, Ohio, 43210-1132, United States
| | - Sharon L. Amacher
- The Ohio State University, Department of Molecular Genetics, Columbus, Ohio, 43210-1132, United States
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6
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Periodic inhibition of Erk activity drives sequential somite segmentation. Nature 2023; 613:153-159. [PMID: 36517597 PMCID: PMC9846577 DOI: 10.1038/s41586-022-05527-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 11/04/2022] [Indexed: 12/23/2022]
Abstract
Sequential segmentation creates modular body plans of diverse metazoan embryos1-4. Somitogenesis establishes the segmental pattern of the vertebrate body axis. A molecular segmentation clock in the presomitic mesoderm sets the pace of somite formation4. However, how cells are primed to form a segment boundary at a specific location remains unclear. Here we developed precise reporters for the clock and double-phosphorylated Erk (ppErk) gradient in zebrafish. We show that the Her1-Her7 oscillator drives segmental commitment by periodically lowering ppErk, therefore projecting its oscillation onto the ppErk gradient. Pulsatile inhibition of the ppErk gradient can fully substitute for the role of the clock, and kinematic clock waves are dispensable for sequential segmentation. The clock functions upstream of ppErk, which in turn enables neighbouring cells to discretely establish somite boundaries in zebrafish5. Molecularly divergent clocks and morphogen gradients were identified in sequentially segmenting species3,4,6-8. Our findings imply that versatile clocks may establish sequential segmentation in diverse species provided that they inhibit gradients.
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7
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Carraco G, Martins-Jesus AP, Andrade RP. The vertebrate Embryo Clock: Common players dancing to a different beat. Front Cell Dev Biol 2022; 10:944016. [PMID: 36036002 PMCID: PMC9403190 DOI: 10.3389/fcell.2022.944016] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Accepted: 07/11/2022] [Indexed: 11/25/2022] Open
Abstract
Vertebrate embryo somitogenesis is the earliest morphological manifestation of the characteristic patterned structure of the adult axial skeleton. Pairs of somites flanking the neural tube are formed periodically during early development, and the molecular mechanisms in temporal control of this early patterning event have been thoroughly studied. The discovery of a molecular Embryo Clock (EC) underlying the periodicity of somite formation shed light on the importance of gene expression dynamics for pattern formation. The EC is now known to be present in all vertebrate organisms studied and this mechanism was also described in limb development and stem cell differentiation. An outstanding question, however, remains unanswered: what sets the different EC paces observed in different organisms and tissues? This review aims to summarize the available knowledge regarding the pace of the EC, its regulation and experimental manipulation and to expose new questions that might help shed light on what is still to unveil.
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Affiliation(s)
- Gil Carraco
- ABC-RI, Algarve Biomedical Center Research Institute, Faro, Portugal
- Faculdade de Medicina e Ciências Biomédicas (FMCB), Universidade do Algarve, Campus de Gambelas, Faro, Portugal
| | | | - Raquel P. Andrade
- ABC-RI, Algarve Biomedical Center Research Institute, Faro, Portugal
- Faculdade de Medicina e Ciências Biomédicas (FMCB), Universidade do Algarve, Campus de Gambelas, Faro, Portugal
- Champalimaud Research Program, Champalimaud Center for the Unknown, Lisbon, Portugal
- *Correspondence: Raquel P. Andrade,
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8
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Zinani OQH, Keseroğlu K, Ay A, Özbudak EM. Pairing of segmentation clock genes drives robust pattern formation. Nature 2020; 589:431-436. [PMID: 33361814 PMCID: PMC7932681 DOI: 10.1038/s41586-020-03055-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 11/03/2020] [Indexed: 12/12/2022]
Abstract
Gene expression is an inherently stochastic process 1,2; however, organismal development and homeostasis require that cells spatiotemporally coordinate the expression of large sets of genes. Coexpressed gene pairs in metazoans often reside in the same chromosomal neighborhood, with gene pairs representing 10% - 50% of all genes depending on species 3–6. As shared upstream regulators can ensure correlated gene expression, the selective advantage of maintaining adjacent gene pairs remains unknown 6. Here, using two linked zebrafish segmentation clock genes, her1 and her7, and combining single-cell transcript counting, genetic engineering, real-time imaging and computational modeling, we reveal that gene pairing boosts correlated transcription and provides phenotypic robustness for developmental pattern formation. Our results demonstrate that disrupting gene pairing disrupts oscillations and segmentation, identifying the selective pressure retaining correlated transcription to sustain a robust and rapid developmental clock. We anticipate that these findings will inspire investigating advantages of gene pairing in other systems and engineering precise synthetic clocks in embryos and organoids.
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Affiliation(s)
- Oriana Q H Zinani
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.,Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Kemal Keseroğlu
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Ahmet Ay
- Department of Biology, Colgate University, Hamilton, NY, USA.,Department of Mathematics, Colgate University, Hamilton, NY, USA
| | - Ertuğrul M Özbudak
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA. .,Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
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9
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Naganathan S, Oates A. Patterning and mechanics of somite boundaries in zebrafish embryos. Semin Cell Dev Biol 2020; 107:170-178. [DOI: 10.1016/j.semcdb.2020.04.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Revised: 03/12/2020] [Accepted: 04/19/2020] [Indexed: 12/12/2022]
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10
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Prajapati RS, Mitter R, Vezzaro A, Ish-Horowicz D. Greb1 is required for axial elongation and segmentation in vertebrate embryos. Biol Open 2020; 9:bio047290. [PMID: 31988092 PMCID: PMC7044451 DOI: 10.1242/bio.047290] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 01/06/2020] [Indexed: 01/08/2023] Open
Abstract
During vertebrate embryonic development, the formation of axial structures is driven by a population of stem-like cells that reside in a region of the tailbud called the chordoneural hinge (CNH). We have compared the mouse CNH transcriptome with those of surrounding tissues and shown that the CNH and tailbud mesoderm are transcriptionally similar, and distinct from the presomitic mesoderm. Amongst CNH-enriched genes are several that are required for axial elongation, including Wnt3a, Cdx2, Brachyury/T and Fgf8, and androgen/oestrogen receptor nuclear signalling components such as Greb1 We show that the pattern and duration of tailbud Greb1 expression is conserved in mouse, zebrafish and chicken embryos, and that Greb1 is required for axial elongation and somitogenesis in zebrafish embryos. The axial truncation phenotype of Greb1 morphant embryos can be explained by much reduced expression of No tail (Ntl/Brachyury), which is required for axial progenitor maintenance. Posterior segmentation defects in the morphants (including misexpression of genes such as mespb, myoD and papC) appear to result, in part, from lost expression of the segmentation clock gene, her7.
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Affiliation(s)
| | - Richard Mitter
- Cancer Research UK Developmental Genetics Laboratory, CRUK London Research Institute
- Francis Crick Institute, 1 Midland Rd, London NW1 1AT, UK
| | - Annalisa Vezzaro
- Cancer Research UK Developmental Genetics Laboratory, CRUK London Research Institute
- Veyrier, 1255, Switzerland
| | - David Ish-Horowicz
- Cancer Research UK Developmental Genetics Laboratory, CRUK London Research Institute
- Cancer Research UK Developmental Genetics Laboratory, and University College London, UK
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11
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A systems biology approach reveals neuronal and muscle developmental defects after chronic exposure to ionising radiation in zebrafish. Sci Rep 2019; 9:20241. [PMID: 31882844 PMCID: PMC6934629 DOI: 10.1038/s41598-019-56590-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 12/13/2019] [Indexed: 11/11/2022] Open
Abstract
Contamination of the environment after the Chernobyl and Fukushima Daiichi nuclear power plant (NPP) disasters led to the exposure of a large number of humans and wild animals to radioactive substances. However, the sub-lethal consequences induced by these absorbed radiological doses remain understudied and the long-term biological impacts largely unknown. We assessed the biological effects of chronic exposure to ionizing radiation (IR) on embryonic development by exposing zebrafish embryo from fertilization and up to 120 hours post-fertilization (hpf) at dose rates of 0.5 mGy/h, 5 mGy/h and 50 mGy/h, thereby encompassing the field of low dose rates defined at 6 mGy/h. Chronic exposure to IR altered larval behaviour in a light-dark locomotor test and affected cardiac activity at a dose rate as low as 0.5 mGy/h. The multi-omics analysis of transcriptome, proteome and transcription factor binding sites in the promoters of the deregulated genes, collectively points towards perturbations of neurogenesis, muscle development, and retinoic acid (RA) signaling after chronic exposure to IR. Whole-mount RNA in situ hybridization confirmed the impaired expression of the transcription factors her4.4 in the central nervous system and myogenin in the developing muscles of exposed embryos. At the organ level, the assessment of muscle histology by transmission electron microscopy (TEM) demonstrated myofibers disruption and altered neuromuscular junctions in exposed larvae at 5 mGy/h and 50 mGy/h. The integration of these multi-level data demonstrates that chronic exposure to low dose rates of IR has an impact on neuronal and muscle progenitor cells, that could lead to motility defects in free swimming larvae at 120 hpf. The mechanistic understanding of these effects allows us to propose a model where deregulation of RA signaling by chronic exposure to IR has pleiotropic effects on neurogenesis and muscle development.
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12
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Ban H, Yokota D, Otosaka S, Kikuchi M, Kinoshita H, Fujino Y, Yabe T, Ovara H, Izuka A, Akama K, Yamasu K, Takada S, Kawamura A. Transcriptional autoregulation of zebrafish tbx6 is required for somite segmentation. Development 2019; 146:dev.177063. [PMID: 31444219 DOI: 10.1242/dev.177063] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 08/15/2019] [Indexed: 12/13/2022]
Abstract
The presumptive somite boundary in the presomitic mesoderm (PSM) is defined by the anterior border of the expression domain of Tbx6 protein. During somite segmentation, the expression domain of Tbx6 is regressed by Ripply-meditated degradation of Tbx6 protein. Although the expression of zebrafish tbx6 remains restricted to the PSM, the transcriptional regulation of tbx6 remains poorly understood. Here, we show that the expression of zebrafish tbx6 is maintained by transcriptional autoregulation. We find that a proximal-located cis-regulatory module, TR1, which contains two putative T-box sites, is required for somite segmentation in the intermediate body and for proper expression of segmentation genes. Embryos with deletion of TR1 exhibit significant reduction of tbx6 expression at the 12-somite stage, although its expression is initially observed. Additionally, Tbx6 is associated with TR1 and activates its own expression in the anterior PSM. Furthermore, the anterior expansion of tbx6 expression in ripply gene mutants is suppressed in a TR1-dependent manner. The results suggest that the autoregulatory loop of zebrafish tbx6 facilitates immediate removal of Tbx6 protein through termination of its own transcription at the anterior PSM.
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Affiliation(s)
- Hiroyuki Ban
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Daisuke Yokota
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Shiori Otosaka
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Morimichi Kikuchi
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Hirofumi Kinoshita
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Yuuri Fujino
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Taijiro Yabe
- Exploratory Research Center on Life and Living Systems and National Institute for Basic Biology, National Institutes of Natural Sciences, Aichi 444-8787, Japan
| | - Hiroki Ovara
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Ayaka Izuka
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Kagari Akama
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Kyo Yamasu
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Shinji Takada
- Exploratory Research Center on Life and Living Systems and National Institute for Basic Biology, National Institutes of Natural Sciences, Aichi 444-8787, Japan
| | - Akinori Kawamura
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
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13
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Lleras Forero L, Narayanan R, Huitema LF, VanBergen M, Apschner A, Peterson-Maduro J, Logister I, Valentin G, Morelli LG, Oates AC, Schulte-Merker S. Segmentation of the zebrafish axial skeleton relies on notochord sheath cells and not on the segmentation clock. eLife 2018; 7:33843. [PMID: 29624170 PMCID: PMC5962341 DOI: 10.7554/elife.33843] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2017] [Accepted: 04/04/2018] [Indexed: 12/12/2022] Open
Abstract
Segmentation of the axial skeleton in amniotes depends on the segmentation clock, which patterns the paraxial mesoderm and the sclerotome. While the segmentation clock clearly operates in teleosts, the role of the sclerotome in establishing the axial skeleton is unclear. We severely disrupt zebrafish paraxial segmentation, yet observe a largely normal segmentation process of the chordacentra. We demonstrate that axial entpd5+ notochord sheath cells are responsible for chordacentrum mineralization, and serve as a marker for axial segmentation. While autonomous within the notochord sheath, entpd5 expression and centrum formation show some plasticity and can respond to myotome pattern. These observations reveal for the first time the dynamics of notochord segmentation in a teleost, and are consistent with an autonomous patterning mechanism that is influenced, but not determined by adjacent paraxial mesoderm. This behavior is not consistent with a clock-type mechanism in the notochord.
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Affiliation(s)
- Laura Lleras Forero
- Institute for Cardiovascular Organogenesis and Regeneration, Faculty of Medicine, WWU Münster, Münster, Germany.,CiM Cluster of Excellence (EXC-1003-CiM), Münster, Germany.,Hubrecht Institute-KNAW & UMC Utrecht, Utrecht, Netherlands
| | | | | | - Maaike VanBergen
- Institute for Cardiovascular Organogenesis and Regeneration, Faculty of Medicine, WWU Münster, Münster, Germany
| | | | | | - Ive Logister
- Hubrecht Institute-KNAW & UMC Utrecht, Utrecht, Netherlands
| | | | - Luis G Morelli
- Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA), CONICET-Partner Institute of the Max Planck Society, Buenos Aires, Argentina.,Departamento de Fisica, FCEyN, UBA, Ciudad Universitaria, Buenos Aires, Argentina.,Department of Systemic Cell Biology, Max Planck Institute for Molecular Physiology, Dortmund, Germany
| | - Andrew C Oates
- The Francis Crick Institute, London, United Kingdom.,Department of Cell and Developmental Biology, University College London, London, United Kingdom.,Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Stefan Schulte-Merker
- Institute for Cardiovascular Organogenesis and Regeneration, Faculty of Medicine, WWU Münster, Münster, Germany
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14
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Trivedi V, Choi HMT, Fraser SE, Pierce NA. Multidimensional quantitative analysis of mRNA expression within intact vertebrate embryos. Development 2018; 145:dev156869. [PMID: 29311262 PMCID: PMC5825878 DOI: 10.1242/dev.156869] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 11/23/2017] [Indexed: 12/29/2022]
Abstract
For decades, in situ hybridization methods have been essential tools for studies of vertebrate development and disease, as they enable qualitative analyses of mRNA expression in an anatomical context. Quantitative mRNA analyses typically sacrifice the anatomy, relying on embryo microdissection, dissociation, cell sorting and/or homogenization. Here, we eliminate the trade-off between quantitation and anatomical context, using quantitative in situ hybridization chain reaction (qHCR) to perform accurate and precise relative quantitation of mRNA expression with subcellular resolution within whole-mount vertebrate embryos. Gene expression can be queried in two directions: read-out from anatomical space to expression space reveals co-expression relationships in selected regions of the specimen; conversely, read-in from multidimensional expression space to anatomical space reveals those anatomical locations in which selected gene co-expression relationships occur. As we demonstrate by examining gene circuits underlying somitogenesis, quantitative read-out and read-in analyses provide the strengths of flow cytometry expression analyses, but by preserving subcellular anatomical context, they enable bi-directional queries that open a new era for in situ hybridization.
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Affiliation(s)
- Vikas Trivedi
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
- Translational Imaging Center, University of Southern California, Los Angeles, CA 90089, USA
- Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
- Department of Genetics, University of Cambridge, Cambridge CB2 3EH, UK
| | - Harry M T Choi
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Scott E Fraser
- Translational Imaging Center, University of Southern California, Los Angeles, CA 90089, USA
- Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Niles A Pierce
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
- Division of Engineering & Applied Science, California Institute of Technology, Pasadena, CA 91125, USA
- Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
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15
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Small molecule screen in embryonic zebrafish using modular variations to target segmentation. Nat Commun 2017; 8:1901. [PMID: 29196645 PMCID: PMC5711842 DOI: 10.1038/s41467-017-01469-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 09/19/2017] [Indexed: 01/19/2023] Open
Abstract
Small molecule in vivo phenotypic screening is used to identify drugs or biological activities by directly assessing effects in intact organisms. However, current screening designs may not exploit the full potential of chemical libraries due to false negatives. Here, we demonstrate a modular small molecule screen in embryonic zebrafish that varies concentration, genotype and timing to target segmentation disorders, birth defects that affect the spinal column. By testing each small molecule in multiple interrelated ways, this screen recovers compounds that a standard screening design would have missed, increasing the hit frequency from the chemical library three-fold. We identify molecular pathways and segmentation phenotypes, which we share in an open-access annotated database. These hits provide insight into human vertebral segmentation disorders and myopathies. This modular screening strategy is applicable to other developmental questions and disease models, highlighting the power of relatively small chemical libraries to accelerate gene discovery and disease study.
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16
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Li J, Yue Y, Dong X, Jia W, Li K, Liang D, Dong Z, Wang X, Nan X, Zhang Q, Zhao Q. Zebrafish foxc1a plays a crucial role in early somitogenesis by restricting the expression of aldh1a2 directly. J Biol Chem 2015; 290:10216-28. [PMID: 25724646 DOI: 10.1074/jbc.m114.612572] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Indexed: 11/06/2022] Open
Abstract
Foxc1a is a member of the forkhead transcription factors. It plays an essential role in zebrafish somitogenesis. However, little is known about the molecular mechanisms underlying its controlling somitogenesis. To uncover how foxc1a regulates zebrafish somitogenesis, we generated foxc1a knock-out zebrafish using TALEN (transcription activator-like effector nuclease) technology. The foxc1a null embryos exhibited defective somites at early development. Analyses on the expressions of the key genes that control processes of somitogenesis revealed that foxc1a controlled early somitogenesis by regulating the expression of myod1. In the somites of foxc1a knock-out embryos, expressions of fgf8a and deltaC were abolished, whereas the expression of aldh1a2 (responsible for providing retinoic acid signaling) was significantly increased. Once the increased retinoic acid level in the foxc1a null embryos was reduced by knocking down aldh1a2, the reduced expression of myod1 was partially rescued by resuming expressions of fgf8a and deltaC in the somites of the mutant embryos. Moreover, a chromatin immunoprecipitation assay on zebrafish embryos revealed that Foxc1a bound aldh1a2 promoter directly. On the other hand, neither knocking down fgf8a nor inhibiting Notch signaling affected the expression of aldh1a2, although knocking down fgf8a reduced expression of deltaC in the somites of zebrafish embryos at early somitogenesis and vice versa. Taken together, our results demonstrate that foxc1a plays an essential role in early somitogenesis by controlling Fgf and Notch signaling through restricting the expression of aldh1a2 in paraxial mesoderm directly.
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Affiliation(s)
- Jingyun Li
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and the Maternal and Child Health Medical Institute, Nanjing Maternal and Child Health Care Hospital Affiliated with Nanjing Medical University, Nanjing 210004, China
| | - Yunyun Yue
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Xiaohua Dong
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Wenshuang Jia
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Kui Li
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Dong Liang
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Zhangji Dong
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Xiaoxiao Wang
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Xiaoxi Nan
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Qinxin Zhang
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
| | - Qingshun Zhao
- From the MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061, China and
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17
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Ay A, Holland J, Sperlea A, Devakanmalai GS, Knierer S, Sangervasi S, Stevenson A, Ozbudak EM. Spatial gradients of protein-level time delays set the pace of the traveling segmentation clock waves. Development 2014; 141:4158-67. [PMID: 25336742 DOI: 10.1242/dev.111930] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The vertebrate segmentation clock is a gene expression oscillator controlling rhythmic segmentation of the vertebral column during embryonic development. The period of oscillations becomes longer as cells are displaced along the posterior to anterior axis, which results in traveling waves of clock gene expression sweeping in the unsegmented tissue. Although various hypotheses necessitating the inclusion of additional regulatory genes into the core clock network at different spatial locations have been proposed, the mechanism underlying traveling waves has remained elusive. Here, we combined molecular-level computational modeling and quantitative experimentation to solve this puzzle. Our model predicts the existence of an increasing gradient of gene expression time delays along the posterior to anterior direction to recapitulate spatiotemporal profiles of the traveling segmentation clock waves in different genetic backgrounds in zebrafish. We validated this prediction by measuring an increased time delay of oscillatory Her1 protein production along the unsegmented tissue. Our results refuted the need for spatial expansion of the core feedback loop to explain the occurrence of traveling waves. Spatial regulation of gene expression time delays is a novel way of creating dynamic patterns; this is the first report demonstrating such a control mechanism in any tissue and future investigations will explore the presence of analogous examples in other biological systems.
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Affiliation(s)
- Ahmet Ay
- Department of Mathematics, Colgate University, Hamilton, NY 13346, USA Department of Biology, Colgate University, Hamilton, NY 13346, USA
| | - Jack Holland
- Department of Computer Science, Colgate University, Hamilton, NY 13346, USA
| | - Adriana Sperlea
- Department of Computer Science, Colgate University, Hamilton, NY 13346, USA
| | | | - Stephan Knierer
- Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | | | - Angel Stevenson
- Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Ertuğrul M Ozbudak
- Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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18
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Maragh S, Miller RA, Bessling SL, Wang G, Hook PW, McCallion AS. Rbm24a and Rbm24b are required for normal somitogenesis. PLoS One 2014; 9:e105460. [PMID: 25170925 PMCID: PMC4149414 DOI: 10.1371/journal.pone.0105460] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 07/24/2014] [Indexed: 12/13/2022] Open
Abstract
We recently demonstrated that the gene encoding the RNA binding motif protein 24 (RBM24) is expressed during mouse cardiogenesis, and determined the developmental requirement for its zebrafish homologs Rbm24a and Rbm24b during cardiac development. We demonstrate here that both Rbm24a and Rbm24b are also required for normal somite and craniofacial development. Diminution of rbm24a or rbm24b gene products by morpholino knockdown resulted in significant disruption of somite formation. Detailed in situ hybridization-based analyses of a spectrum of somitogenesis-associated transcripts revealed reduced expression of the cyclic muscle pattering genes dlc and dld encoding Notch ligands, as well as their respective target genes her7, her1. By contrast expression of the Notch receptors notch1a and notch3 appears unchanged. Some RBM-family members have been implicated in pre-mRNA processing. Analysis of affected Notch-pathway mRNAs in rbm24a and rbm24b morpholino-injected embryos revealed aberrant transcript fragments of dlc and dld, but not her1 or her7, suggesting the reduction in transcription levels of Notch pathway components may result from aberrant processing of its ligands. These data imply a previously unknown requirement for Rbm24a and Rbm24b in somite and craniofacial development. Although we anticipate the influence of disrupting RBM24 homologs likely extends beyond the Notch pathway, our results suggest their perturbation may directly, or indirectly, compromise post-transcriptional processing, exemplified by imprecise processing of dlc and dld.
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Affiliation(s)
- Samantha Maragh
- Biochemical Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States of America
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Ronald A. Miller
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Seneca L. Bessling
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Guangliang Wang
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Paul W. Hook
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Andrew S. McCallion
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- * E-mail:
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19
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Modeling the zebrafish segmentation clock's gene regulatory network constrained by expression data suggests evolutionary transitions between oscillating and nonoscillating transcription. Genetics 2014; 197:725-38. [PMID: 24663100 DOI: 10.1534/genetics.114.163642] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
During segmentation of vertebrate embryos, somites form in accordance with a periodic pattern established by the segmentation clock. In the zebrafish (Danio rerio), the segmentation clock includes six hairy/enhancer of split-related (her/hes) genes, five of which oscillate due to negative autofeedback. The nonoscillating gene hes6 forms the hub of a network of 10 Her/Hes protein dimers, which includes 7 DNA-binding dimers and 4 weak or non-DNA-binding dimers. The balance of dimer species is critical for segmentation clock function, and loss-of-function studies suggest that the her genes have both unique and redundant functions within the clock. However, the precise regulatory interactions underlying the negative feedback loop are unknown. Here, we combine quantitative experimental data, in silico modeling, and a global optimization algorithm to identify a gene regulatory network (GRN) designed to fit measured transcriptional responses to gene knockdown. Surprisingly, we find that hes6, the clock gene that does not oscillate, responds to negative feedback. Consistent with prior in silico analyses, we find that variation in transcription, translation, and degradation rates can mediate the gain and loss of oscillatory behavior for genes regulated by negative feedback. Extending our study, we found that transcription of the nonoscillating Fgf pathway gene sef responds to her/hes perturbation similarly to oscillating her genes. These observations suggest a more extensive underlying regulatory similarity between the zebrafish segmentation clock and the mouse and chick segmentation clocks, which exhibit oscillations of her/hes genes as well as numerous other Notch, Fgf, and Wnt pathway genes.
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20
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Ay A, Knierer S, Sperlea A, Holland J, Özbudak EM. Short-lived Her proteins drive robust synchronized oscillations in the zebrafish segmentation clock. Development 2013; 140:3244-53. [DOI: 10.1242/dev.093278] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Oscillations are prevalent in natural systems. A gene expression oscillator, called the segmentation clock, controls segmentation of precursors of the vertebral column. Genes belonging to the Hes/her family encode the only conserved oscillating genes in all analyzed vertebrate species. Hes/Her proteins form dimers and negatively autoregulate their own transcription. Here, we developed a stochastic two-dimensional multicellular computational model to elucidate how the dynamics, i.e. period, amplitude and synchronization, of the segmentation clock are regulated. We performed parameter searches to demonstrate that autoregulatory negative-feedback loops of the redundant repressor Her dimers can generate synchronized gene expression oscillations in wild-type embryos and reproduce the dynamics of the segmentation oscillator in different mutant conditions. Our model also predicts that synchronized oscillations can be robustly generated as long as the half-lives of the repressor dimers are shorter than 6 minutes. We validated this prediction by measuring, for the first time, the half-life of Her7 protein as 3.5 minutes. These results demonstrate the importance of building biologically realistic stochastic models to test biological models more stringently and make predictions for future experimental studies.
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Affiliation(s)
- Ahmet Ay
- Department of Mathematics, Colgate University, Hamilton, NY 13346, USA
- Department of Biology, Colgate University, Hamilton, NY 13346, USA
| | - Stephan Knierer
- Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Adriana Sperlea
- Department of Computer Science, Colgate University, Hamilton, NY 13346, USA
| | - Jack Holland
- Department of Computer Science, Colgate University, Hamilton, NY 13346, USA
| | - Ertuğrul M. Özbudak
- Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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21
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Hanisch A, Holder MV, Choorapoikayil S, Gajewski M, Özbudak EM, Lewis J. The elongation rate of RNA polymerase II in zebrafish and its significance in the somite segmentation clock. Development 2013; 140:444-53. [PMID: 23250218 DOI: 10.1242/dev.077230] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
A gene expression oscillator called the segmentation clock controls somite segmentation in the vertebrate embryo. In zebrafish, the oscillatory transcriptional repressor genes her1 and her7 are crucial for genesis of the oscillations, which are thought to arise from negative autoregulation of these genes. The period of oscillation is predicted to depend on delays in the negative-feedback loop, including, most importantly, the transcriptional delay - the time taken to make each molecule of her1 or her7 mRNA. her1 and her7 operate in parallel. Loss of both gene functions, or mutation of her1 combined with knockdown of Hes6, which we show to be a binding partner of Her7, disrupts segmentation drastically. However, mutants in which only her1 or her7 is functional show only mild segmentation defects and their oscillations have almost identical periods. This is unexpected because the her1 and her7 genes differ greatly in length. We use transgenic zebrafish to measure the RNA polymerase II elongation rate, for the first time, in the intact embryo. This rate is unexpectedly rapid, at 4.8 kb/minute at 28.5°C, implying that, for both genes, the time taken for transcript elongation is insignificant compared with other sources of delay, explaining why the mutants have similar clock periods. Our computational model shows how loss of her1 or her7 can allow oscillations to continue with unchanged period but with reduced amplitude and impaired synchrony, as manifested in the in situ hybridisation patterns of the single mutants.
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Affiliation(s)
- Anja Hanisch
- Vertebrate Development Laboratory, Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK
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