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Chadha Y, Khurana A, Schmoller KM. Eukaryotic cell size regulation and its implications for cellular function and dysfunction. Physiol Rev 2024; 104:1679-1717. [PMID: 38900644 DOI: 10.1152/physrev.00046.2023] [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: 12/26/2023] [Revised: 05/24/2024] [Accepted: 06/19/2024] [Indexed: 06/22/2024] Open
Abstract
Depending on cell type, environmental inputs, and disease, the cells in the human body can have widely different sizes. In recent years, it has become clear that cell size is a major regulator of cell function. However, we are only beginning to understand how the optimization of cell function determines a given cell's optimal size. Here, we review currently known size control strategies of eukaryotic cells and the intricate link of cell size to intracellular biomolecular scaling, organelle homeostasis, and cell cycle progression. We detail the cell size-dependent regulation of early development and the impact of cell size on cell differentiation. Given the importance of cell size for normal cellular physiology, cell size control must account for changing environmental conditions. We describe how cells sense environmental stimuli, such as nutrient availability, and accordingly adapt their size by regulating cell growth and cell cycle progression. Moreover, we discuss the correlation of pathological states with misregulation of cell size and how for a long time this was considered a downstream consequence of cellular dysfunction. We review newer studies that reveal a reversed causality, with misregulated cell size leading to pathophysiological phenotypes such as senescence and aging. In summary, we highlight the important roles of cell size in cellular function and dysfunction, which could have major implications for both diagnostics and treatment in the clinic.
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Affiliation(s)
- Yagya Chadha
- Institute of Functional Epigenetics, Molecular Targets and Therapeutics Center, Helmholtz Zentrum München, Neuherberg, Germany
| | - Arohi Khurana
- Institute of Functional Epigenetics, Molecular Targets and Therapeutics Center, Helmholtz Zentrum München, Neuherberg, Germany
| | - Kurt M Schmoller
- Institute of Functional Epigenetics, Molecular Targets and Therapeutics Center, Helmholtz Zentrum München, Neuherberg, Germany
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2
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Schindler-Johnson M, Petridou NI. Collective effects of cell cleavage dynamics. Front Cell Dev Biol 2024; 12:1358971. [PMID: 38559810 PMCID: PMC10978805 DOI: 10.3389/fcell.2024.1358971] [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: 12/20/2023] [Accepted: 03/05/2024] [Indexed: 04/04/2024] Open
Abstract
A conserved process of early embryonic development in metazoans is the reductive cell divisions following oocyte fertilization, termed cell cleavages. Cell cleavage cycles usually start synchronously, lengthen differentially between the embryonic cells becoming asynchronous, and cease before major morphogenetic events, such as germ layer formation and gastrulation. Despite exhibiting species-specific characteristics, the regulation of cell cleavage dynamics comes down to common controllers acting mostly at the single cell/nucleus level, such as nucleus-to-cytoplasmic ratio and zygotic genome activation. Remarkably, recent work has linked cell cleavage dynamics to the emergence of collective behavior during embryogenesis, including pattern formation and changes in embryo-scale mechanics, raising the question how single-cell controllers coordinate embryo-scale processes. In this review, we summarize studies across species where an association between cell cleavages and collective behavior was made, discuss the underlying mechanisms, and propose that cell-to-cell variability in cell cleavage dynamics can serve as a mechanism of long-range coordination in developing embryos.
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Affiliation(s)
- Magdalena Schindler-Johnson
- Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
- Faculty of Biosciences, Heidelberg University, Heidelberg, Germany
| | - Nicoletta I. Petridou
- Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
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3
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Harrison MM, Marsh AJ, Rushlow CA. Setting the stage for development: the maternal-to-zygotic transition in Drosophila. Genetics 2023; 225:iyad142. [PMID: 37616526 PMCID: PMC10550319 DOI: 10.1093/genetics/iyad142] [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: 05/18/2023] [Accepted: 07/18/2023] [Indexed: 08/26/2023] Open
Abstract
The zygote has a daunting task ahead of itself; it must develop from a single cell (fertilized egg) into a fully functioning adult with a multitude of different cell types. In the beginning, the zygote has help from its mother, in the form of gene products deposited into the egg, but eventually, it must rely on its own resources to proceed through development. The transfer of developmental control from the mother to the embryo is called the maternal-to-zygotic transition (MZT). All animals undergo this transition, which is defined by two main processes-the degradation of maternal RNAs and the synthesis of new RNAs from the zygote's own genome. Here, we review the regulation of the MZT in Drosophila, but given the broad conservation of this essential process, much of the regulation is shared among metazoans.
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Affiliation(s)
- Melissa M Harrison
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI 53706USA
| | - Audrey J Marsh
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI 53706USA
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4
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Olivetta M, Dudin O. The nuclear-to-cytoplasmic ratio drives cellularization in the close animal relative Sphaeroforma arctica. Curr Biol 2023; 33:1597-1605.e3. [PMID: 36996815 DOI: 10.1016/j.cub.2023.03.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 02/17/2023] [Accepted: 03/07/2023] [Indexed: 03/31/2023]
Abstract
The ratio of nuclear content to cytoplasmic volume (N/C ratio) is a key regulator driving the maternal-to-zygotic transition in most animal embryos. Altering this ratio often impacts zygotic genome activation and deregulates the timing and outcome of embryogenesis.1,2,3 Despite being ubiquitous across animals, little is known about when the N/C ratio evolved to control multicellular development. Such capacity either originated with the emergence of animal multicellularity or was co-opted from the mechanisms present in unicellular organisms.4 An effective strategy to tackle this question is to investigate the close relatives of animals exhibiting life cycles with transient multicellular stages.5 Among these are ichthyosporeans, a lineage of protists undergoing coenocytic development followed by cellularization and cell release.6,7,8 During cellularization, a transient multicellular stage resembling animal epithelia is generated, offering a unique opportunity to examine whether the N/C ratio regulates multicellular development. Here, we use time-lapse microscopy to characterize how the N/C ratio affects the life cycle of the best-studied ichthyosporean model, Sphaeroforma arctica. We uncover that the last stages of cellularization coincide with a significant increase in the N/C ratio. Increasing the N/C ratio by reducing the coenocytic volume accelerates cellularization, whereas decreasing the N/C ratio by lowering the nuclear content halts it. Moreover, centrifugation and pharmacological inhibitor experiments suggest that the N/C ratio is locally sensed at the cortex and relies on phosphatase activity. Altogether, our results show that the N/C ratio drives cellularization in S. arctica, suggesting that its capacity to control multicellular development predates animal emergence.
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5
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McCartney B, Dudin O. Cellularization across eukaryotes: Conserved mechanisms and novel strategies. Curr Opin Cell Biol 2023; 80:102157. [PMID: 36857882 DOI: 10.1016/j.ceb.2023.102157] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 01/27/2023] [Accepted: 01/31/2023] [Indexed: 03/02/2023]
Abstract
Many eukaryotes form multinucleated cells during their development. Some cells persist as such during their lifetime, others choose to cleave each nucleus individually using a specialized cytokinetic process known as cellularization. What is cellularization and how is it achieved across the eukaryotic tree of life? Are there common pathways among all species supporting a shared ancestry, or are there key differences, suggesting independent evolutionary paths? In this review, we discuss common strategies and key mechanistic differences in how cellularization is executed across vastly divergent eukaryotic species. We present a number of novel methods and non-model organisms that may provide important insight into the evolutionary origins of cellularization.
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Affiliation(s)
- Brooke McCartney
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
| | - Omaya Dudin
- Swiss Institute for Experimental Cancer Research, School of Life Sciences, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
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6
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Sokac AM, Biel N, De Renzis S. Membrane-actin interactions in morphogenesis: Lessons learned from Drosophila cellularization. Semin Cell Dev Biol 2023; 133:107-122. [PMID: 35396167 PMCID: PMC9532467 DOI: 10.1016/j.semcdb.2022.03.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Revised: 03/18/2022] [Accepted: 03/21/2022] [Indexed: 01/12/2023]
Abstract
During morphogenesis, changes in the shapes of individual cells are harnessed to mold an entire tissue. These changes in cell shapes require the coupled remodeling of the plasma membrane and underlying actin cytoskeleton. In this review, we highlight cellularization of the Drosophila embryo as a model system to uncover principles of how membrane and actin dynamics are co-regulated in space and time to drive morphogenesis.
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Affiliation(s)
- Anna Marie Sokac
- Department of Cell and Developmental Biology, University of Illinois at Urbana Champaign, Urbana, IL 61801, USA; Graduate Program in Integrative and Molecular Biomedical Sciences, Baylor College of Medicine, Houston, TX 77030, USA.
| | - Natalie Biel
- Department of Cell and Developmental Biology, University of Illinois at Urbana Champaign, Urbana, IL 61801, USA; Graduate Program in Integrative and Molecular Biomedical Sciences, Baylor College of Medicine, Houston, TX 77030, USA
| | - Stefano De Renzis
- European Molecular Biology Laboratory Heidelberg, 69117 Heidelberg, Germany
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7
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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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8
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Balachandra S, Sarkar S, Amodeo AA. The Nuclear-to-Cytoplasmic Ratio: Coupling DNA Content to Cell Size, Cell Cycle, and Biosynthetic Capacity. Annu Rev Genet 2022; 56:165-185. [PMID: 35977407 PMCID: PMC10165727 DOI: 10.1146/annurev-genet-080320-030537] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Though cell size varies between different cells and across species, the nuclear-to-cytoplasmic (N/C) ratio is largely maintained across species and within cell types. A cell maintains a relatively constant N/C ratio by coupling DNA content, nuclear size, and cell size. We explore how cells couple cell division and growth to DNA content. In some cases, cells use DNA as a molecular yardstick to control the availability of cell cycle regulators. In other cases, DNA sets a limit for biosynthetic capacity. Developmentally programmed variations in the N/C ratio for a given cell type suggest that a specific N/C ratio is required to respond to given physiological demands. Recent observations connecting decreased N/C ratios with cellular senescence indicate that maintaining the proper N/C ratio is essential for proper cellular functioning. Together, these findings suggest a causative, not simply correlative, role for the N/C ratio in regulating cell growth and cell cycle progression.
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Affiliation(s)
- Shruthi Balachandra
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, USA; ,
| | - Sharanya Sarkar
- Department of Microbiology and Immunology, Dartmouth College, Hanover, New Hampshire, USA;
| | - Amanda A Amodeo
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, USA; ,
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9
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Chen H, Good MC. Nascent transcriptome reveals orchestration of zygotic genome activation in early embryogenesis. Curr Biol 2022; 32:4314-4324.e7. [PMID: 36007528 PMCID: PMC9560990 DOI: 10.1016/j.cub.2022.07.078] [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: 02/01/2022] [Revised: 04/25/2022] [Accepted: 07/29/2022] [Indexed: 12/14/2022]
Abstract
Early embryo development requires maternal-to-zygotic transition, during which transcriptionally silent nuclei begin widespread gene expression during zygotic genome activation (ZGA).1-3 ZGA is vital for early cell fating and germ-layer specification,3,4 and ZGA timing is regulated by multiple mechanisms.1-5 However, controversies remain about whether these mechanisms are interrelated and vary among species6-10 and whether the timing of germ-layer-specific gene activation is temporally ordered.11,12 In some embryonic models, widespread ZGA onset is spatiotemporally graded,13,14 yet it is unclear whether the transcriptome follows this pattern. A major challenge in addressing these questions is to accurately measure the timing of each gene activation. Here, we metabolically label and identify the nascent transcriptome using 5-ethynyl uridine (5-EU) in Xenopus blastula embryos. We find that EU-RNA-seq outperforms total RNA-seq in detecting the ZGA transcriptome, which is dominated by transcription from maternal-zygotic genes, enabling improved ZGA timing determination. We uncover discrete spatiotemporal patterns for individual gene activation, a majority following a spatial pattern of ZGA that is correlated with a cell size gradient.14 We further reveal that transcription necessitates a period of developmental progression and that ZGA can be precociously induced by cycloheximide, potentially through elongation of interphase. Finally, most ectodermal genes are activated earlier than endodermal genes, suggesting a temporal orchestration of germ-layer-specific genes, potentially linked to the spatially graded pattern of ZGA. Together, our study provides fundamental new insights into the composition and dynamics of the ZGA transcriptome, mechanisms regulating ZGA timing, and its role in the onset of early cell fating.
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Affiliation(s)
- Hui Chen
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Matthew C Good
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA.
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10
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Xiao L, Fan D, Qi H, Cong Y, Du Z. Defect-buffering cellular plasticity increases robustness of metazoan embryogenesis. Cell Syst 2022; 13:615-630.e9. [PMID: 35882226 DOI: 10.1016/j.cels.2022.07.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 04/14/2022] [Accepted: 06/30/2022] [Indexed: 01/26/2023]
Abstract
Developmental processes are intrinsically robust so as to preserve a normal-like state in response to genetic and environmental fluctuations. However, the robustness and potential phenotypic plasticity of individual developing cells under genetic perturbations remain to be systematically evaluated. Using large-scale gene perturbation, live imaging, lineage tracing, and single-cell phenomics, we quantified the phenotypic landscape of C. elegans embryogenesis in >2,000 embryos following individual knockdown of over 750 conserved genes. We observed that cellular genetic systems are not sufficiently robust to single-gene perturbations across all cells; rather, gene knockdowns frequently induced cellular defects. Dynamic phenotypic analyses revealed many cellular defects to be transient, with cells exhibiting phenotypic plasticity that serves to alleviate, correct, and accommodate the defects. Moreover, potential developmentally related cell modules may buffer the phenotypic effects of individual cell position changes. Our findings reveal non-negligible contributions of cellular plasticity and multicellularity as compensatory strategies to increase developmental robustness.
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Affiliation(s)
- Long Xiao
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Duchangjiang Fan
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Huan Qi
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Yulin Cong
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhuo Du
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China.
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11
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Hayden L, Chao A, Deneke VE, Vergassola M, Puliafito A, Di Talia S. Cullin-5 mutants reveal collective sensing of the nucleocytoplasmic ratio in Drosophila embryogenesis. Curr Biol 2022; 32:2084-2092.e4. [PMID: 35334230 PMCID: PMC9090985 DOI: 10.1016/j.cub.2022.03.007] [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: 01/21/2022] [Revised: 02/27/2022] [Accepted: 03/01/2022] [Indexed: 11/28/2022]
Abstract
In most metazoans, early embryonic development is characterized by rapid division cycles that pause before gastrulation at the midblastula transition (MBT).1 These cleavage divisions are accompanied by cytoskeletal rearrangements that ensure proper nuclear positioning. However, the molecular mechanisms controlling nuclear positioning are not fully elucidated. In Drosophila, early embryogenesis unfolds in a multinucleated syncytium. Nuclei rapidly move across the anterior-posterior (AP) axis at cell cycles 4-6 in a process driven by actomyosin contractility and cytoplasmic flows.2,3 In shackleton (shkl) mutants, this axial spreading is impaired.4 Here, we show that shkl mutants carry mutations in the cullin-5 (cul-5) gene. Live imaging experiments show that Cul-5 is downstream of the cell cycle but is required for cortical actomyosin contractility. The nuclear spreading phenotype of cul-5 mutants can be rescued by reducing Src activity, suggesting that a major target of cul-5 is Src kinase. cul-5 mutants display gradients of nuclear density across the AP axis that we exploit to study cell-cycle control as a function of the N/C ratio. We found that the N/C ratio is sensed collectively in neighborhoods of about 100 μm, and such collective sensing is required for a precise MBT, in which all the nuclei in the embryo pause their division cycle. Moreover, we found that the response to the N/C ratio is slightly graded along the AP axis. These two features can be linked to Cdk1 dynamics. Collectively, we reveal a new pathway controlling nuclear positioning and provide a dissection of how nuclear cycles respond to the N/C ratio.
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Affiliation(s)
- Luke Hayden
- Department of Cell Biology, Duke University School of Medicine, Durham, NC 27710, USA
| | - Anna Chao
- Department of Cell Biology, Duke University School of Medicine, Durham, NC 27710, USA
| | - Victoria E Deneke
- Department of Cell Biology, Duke University School of Medicine, Durham, NC 27710, USA
| | - Massimo Vergassola
- Laboratoire de physique de l'École Normale Supérieure, CNRS, PSL Research University, Sorbonne Université, Paris, France; Department of Physics, University of California, San Diego, La Jolla, CA, USA
| | - Alberto Puliafito
- Candiolo Cancer Institute, FPO-IRCCS, Laboratory of Cell Migration, 10060 Candiolo, Italy; Department of Oncology, Università di Torino, 10060 Candiolo, Italy
| | - Stefano Di Talia
- Department of Cell Biology, Duke University School of Medicine, Durham, NC 27710, USA.
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12
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Restriction of subapical proteins during cellularization depends on the onset of zygotic transcription and the formin Dia. Dev Biol 2022; 487:110-121. [PMID: 35525304 DOI: 10.1016/j.ydbio.2022.04.012] [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: 11/18/2021] [Revised: 04/25/2022] [Accepted: 04/28/2022] [Indexed: 11/21/2022]
Abstract
Cortical domains are characterized by spatially restricted polarity proteins. The pattern of cortical domains is dynamic and changes during cell differentiation and development. Although there is a good understanding for how the cortical pattern is maintained, e. g. by mutual antagonism, less is known about how the initial pattern is established, and its dynamics coordinated with developmental progression. Here we investigate the initial restriction of subapical marker proteins during the syncytial-cellular transition in Drosophila embryos. The subapical markers Canoe/Afadin, the complex ELMO-Sponge, Baz and Arm become initially restricted between apical and lateral domains during cellularization. We define the role of zygotic genome activation as a timer for subapical domain formation. Subapical markers remained widely spread in embryos treated with α-amanitin and became precociously restricted in mutant embryos with premature zygotic transcription. In contrast, remodeling of the nuclear division cycle without cytokinesis to a full cell cycle is not a prerequisite for subapical domain formation, since we observed timely subapical restriction in embryos undergoing an extra nuclear cycle. We provide evidence that earliest subapical markers ELMO-Sponge and Canoe are required for subapical accumulation of Baz. Supporting an important role of cortical F-actin in subapical restriction, we found that the formin Dia was required for Baz restriction, and its distribution depended on the onset of zygotic gene expression. In summary, we define zygotic transcription as a timer, to which subapical markers respond in a dia-dependent mechanism.
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13
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Ferree PL, Xing M, Zhang JQ, Di Talia S. Structure-function analysis of Cdc25 Twine degradation at the Drosophila maternal-to-zygotic transition. Fly (Austin) 2022; 16:111-117. [PMID: 35227166 PMCID: PMC8890428 DOI: 10.1080/19336934.2022.2043095] [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: 12/04/2022] Open
Abstract
Downregulation of protein phosphatase Cdc25Twine activity is linked to remodelling of the cell cycle during the Drosophila maternal-to-zygotic transition (MZT). Here, we present a structure-function analysis of Cdc25Twine. We use chimeras to show that the N-terminus regions of Cdc25Twine and Cdc25String control their differential degradation dynamics. Deletion of different regions of Cdc25Twine reveals a putative domain involved in and required for its rapid degradation during the MZT. Notably, a very similar domain is present in Cdc25String and deletion of the DNA replication checkpoint results in similar dynamics of degradation of both Cdc25String and Cdc25Twine. Finally, we show that Cdc25Twine degradation is delayed in embryos lacking the left arm of chromosome III. Thus, we propose a model for the differential regulation of Cdc25 at the Drosophila MZT.
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Affiliation(s)
- Patrick L Ferree
- Department of Cell Biology, Duke University Medical Center, Durham, NC, USA
| | - Maggie Xing
- Department of Cell Biology, Duke University Medical Center, Durham, NC, USA
| | - Jenny Q Zhang
- Department of Surgery, Alpert Medical School, Brown University, Providence, RI, USA
| | - Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham, NC, USA
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14
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Jukam D, Kapoor RR, Straight AF, Skotheim JM. The DNA-to-cytoplasm ratio broadly activates zygotic gene expression in Xenopus. Curr Biol 2021; 31:4269-4281.e8. [PMID: 34388374 DOI: 10.1016/j.cub.2021.07.035] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 05/13/2021] [Accepted: 07/14/2021] [Indexed: 10/20/2022]
Abstract
In multicellular animals, the first major event after fertilization is the switch from maternal to zygotic control of development. During this transition, zygotic gene transcription is broadly activated in an otherwise quiescent genome in a process known as zygotic genome activation (ZGA). In fast-developing embryos, ZGA often overlaps with the slowing of initially synchronous cell divisions at the mid-blastula transition (MBT). Initial studies of the MBT led to the nuclear-to-cytoplasmic ratio model where MBT timing is regulated by the exponentially increasing amounts of some nuclear component "N" titrated against a fixed cytoplasmic component "C." However, more recent experiments have been interpreted to suggest that ZGA is independent of the N/C ratio. To determine the role of the N/C ratio in ZGA, we generated Xenopus frog embryos with ∼3-fold differences in genomic DNA (i.e., N) by using X. tropicalis sperm to fertilize X. laevis eggs with or without their maternal genome. Resulting embryos have otherwise identical X. tropicalis genome template amounts, embryo sizes, and X. laevis maternal environments. We generated transcriptomic time series across the MBT in both conditions and used X. tropicalis paternally derived mRNA to identify a high-confidence set of exclusively zygotic transcripts. Both ZGA and the increase in cell-cycle duration are delayed in embryos with ∼3-fold less DNA per cell. Thus, DNA is an important component of the N/C ratio, which is a critical regulator of zygotic genome activation in Xenopus embryos.
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Affiliation(s)
- David Jukam
- Department of Biology, Stanford University, Stanford, CA 94305, USA; Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Rishabh R Kapoor
- Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - Aaron F Straight
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Jan M Skotheim
- Department of Biology, Stanford University, Stanford, CA 94305, USA.
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15
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Liu B, Zhao H, Wu K, Großhans J. Temporal Gradients Controlling Embryonic Cell Cycle. BIOLOGY 2021; 10:biology10060513. [PMID: 34207742 PMCID: PMC8228447 DOI: 10.3390/biology10060513] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 06/05/2021] [Accepted: 06/07/2021] [Indexed: 12/17/2022]
Abstract
Simple Summary Embryonic cells sense temporal gradients of regulatory signals to determine whether and when to proceed or remodel the cell cycle. Such a control mechanism is allowed to accurately link the cell cycle with the developmental program, including cell differentiation, morphogenesis, and gene expression. The mid-blastula transition has been a paradigm for timing in early embryogenesis in frog, fish, and fly, among others. It has been argued for decades now if the events associated with the mid-blastula transition, i.e., the onset of zygotic gene expression, remodeling of the cell cycle, and morphological changes, are determined by a control mechanism or by absolute time. Recent studies indicate that multiple independent signals and mechanisms contribute to the timing of these different processes. Here, we focus on the mechanisms for cell cycle remodeling, specifically in Drosophila, which relies on gradual changes of the signal over time. We discuss pathways for checkpoint activation, decay of Cdc25 protein levels, as well as depletion of deoxyribonucleotide metabolites and histone proteins. The gradual changes of these signals are linked to Cdk1 activity by readout mechanisms involving thresholds. Abstract Cell proliferation in early embryos by rapid cell cycles and its abrupt pause after a stereotypic number of divisions present an attractive system to study the timing mechanism in general and its coordination with developmental progression. In animals with large eggs, such as Xenopus, zebrafish, or Drosophila, 11–13 very fast and synchronous cycles are followed by a pause or slowdown of the cell cycle. The stage when the cell cycle is remodeled falls together with changes in cell behavior and activation of the zygotic genome and is often referred to as mid-blastula transition. The number of fast embryonic cell cycles represents a clear and binary readout of timing. Several factors controlling the cell cycle undergo dynamics and gradual changes in activity or concentration and thus may serve as temporal gradients. Recent studies have revealed that the gradual loss of Cdc25 protein, gradual depletion of free deoxyribonucleotide metabolites, or gradual depletion of free histone proteins impinge on Cdk1 activity in a threshold-like manner. In this review, we will highlight with a focus on Drosophila studies our current understanding and recent findings on the generation and readout of these temporal gradients, as well as their position within the regulatory network of the embryonic cell cycle.
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Affiliation(s)
- Boyang Liu
- Center for Reproductive Medicine, Cheeloo College of Medicine, Shandong University, Jinan 250012, China; (B.L.); (H.Z.); (K.W.)
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan 250012, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan 250012, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan 250012, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan 250012, China
| | - Han Zhao
- Center for Reproductive Medicine, Cheeloo College of Medicine, Shandong University, Jinan 250012, China; (B.L.); (H.Z.); (K.W.)
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan 250012, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan 250012, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan 250012, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan 250012, China
| | - Keliang Wu
- Center for Reproductive Medicine, Cheeloo College of Medicine, Shandong University, Jinan 250012, China; (B.L.); (H.Z.); (K.W.)
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan 250012, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan 250012, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan 250012, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan 250012, China
| | - Jörg Großhans
- Department of Biology, Philipps University, 35043 Marburg, Germany
- Correspondence:
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16
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The nuclear to cytoplasmic ratio directly regulates zygotic transcription in Drosophila through multiple modalities. Proc Natl Acad Sci U S A 2021; 118:2010210118. [PMID: 33790005 DOI: 10.1073/pnas.2010210118] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Early embryos must rapidly generate large numbers of cells to form an organism. Many species accomplish this through a series of rapid, reductive, and transcriptionally silent cleavage divisions. Previous work has demonstrated that the number of divisions before both cell cycle elongation and zygotic genome activation (ZGA) is regulated by the ratio of nuclear content to cytoplasm (N/C). To understand how the N/C ratio affects the timing of ZGA, we directly assayed the behavior of several previously identified N/C ratio-dependent genes using the MS2-MCP reporter system in living Drosophila embryos with altered ploidy and cell cycle durations. For every gene that we examined, we found that nascent RNA output per cycle is delayed in haploid embryos. Moreover, we found that the N/C ratio influences transcription through three overlapping modes of action. For some genes (knirps, fushi tarazu, and snail), the effect of ploidy can be primarily attributed to changes in cell cycle duration. However, additional N/C ratio-mediated mechanisms contribute significantly to transcription delays for other genes. For giant and bottleneck, the kinetics of transcription activation are significantly disrupted in haploids, while for frühstart and Krüppel, the N/C ratio controls the probability of transcription initiation. Our data demonstrate that the regulatory elements of N/C ratio-dependent genes respond directly to the N/C ratio through multiple modes of regulation.
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17
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Falahati H, Hur W, Di Talia S, Wieschaus E. Temperature-Induced uncoupling of cell cycle regulators. Dev Biol 2020; 470:147-153. [PMID: 33278404 DOI: 10.1016/j.ydbio.2020.11.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 11/23/2020] [Accepted: 11/24/2020] [Indexed: 12/24/2022]
Abstract
The early stages of development involve complex sequences of morphological changes that are both reproducible from embryo to embryo and often robust to environmental variability. To investigate the relationship between reproducibility and robustness we examined cell cycle progression in early Drosophila embryos at different temperatures. Our experiments show that while the subdivision of cell cycle steps is conserved across a wide range of temperatures (5-35 °C), the relative duration of individual steps varies with temperature. We find that the transition into prometaphase is delayed at lower temperatures relative to other cell cycle events, arguing that it has a different mechanism of regulation. Using an in vivo biosensor, we quantified the ratio of activities of the major mitotic kinase, Cdk1 and one of the major mitotic phosphatases PP1. Comparing activation profile with cell cycle transition times at different temperatures indicates that in early fly embryos activation of Cdk1 drives entry into prometaphase but is not required for earlier cell cycle events. In fact, chromosome condensation can still occur when Cdk1 activity is inhibited pharmacologically. These results demonstrate that different kinases are rate-limiting for different steps of mitosis, arguing that robust inter-regulation may be needed for rapid and ordered mitosis.
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Affiliation(s)
- Hanieh Falahati
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544, USA
| | - Woonyung Hur
- Department of Cell Biology, Duke University Medical Center, Durham, NC, 27710, USA
| | - Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham, NC, 27710, USA
| | - Eric Wieschaus
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544, USA; Howard Hughes Medical Institute, Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, USA.
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18
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Chen H, Qian W, Good MC. Integrating cellular dimensions with cell differentiation during early development. Curr Opin Cell Biol 2020; 67:109-117. [PMID: 33152556 DOI: 10.1016/j.ceb.2020.08.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 07/14/2020] [Accepted: 08/03/2020] [Indexed: 11/25/2022]
Abstract
Early embryo development is characterized by alteration of cellular dimensions and fating of blastomeres. An emerging concept is that cell size and shape drive cellular differentiation during early embryogenesis in a variety of model organisms. In this review, we summarize recent advances that elucidate the contribution of the physical dimensions of a cell to major embryonic transitions and cell fate specification in vivo. We also highlight techniques and newly evolving methods for manipulating the sizes and shapes of cells and whole embryos in situ and ex vivo. Finally, we provide an outlook for addressing fundamental questions in the field and more broadly uncovering how changes to cell size control decision making in a variety of biological contexts.
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Affiliation(s)
- Hui Chen
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Wenchao Qian
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Matthew C Good
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA.
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19
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Strong IJT, Lei X, Chen F, Yuan K, O’Farrell PH. Interphase-arrested Drosophila embryos activate zygotic gene expression and initiate mid-blastula transition events at a low nuclear-cytoplasmic ratio. PLoS Biol 2020; 18:e3000891. [PMID: 33090988 PMCID: PMC7608951 DOI: 10.1371/journal.pbio.3000891] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 11/03/2020] [Accepted: 09/14/2020] [Indexed: 11/18/2022] Open
Abstract
Externally deposited eggs begin development with an immense cytoplasm and a single overwhelmed nucleus. Rapid mitotic cycles restore normality as the ratio of nuclei to cytoplasm (N/C) increases. A threshold N/C has been widely proposed to activate zygotic genome transcription and onset of morphogenesis at the mid-blastula transition (MBT). To test whether a threshold N/C is required for these events, we blocked N/C increase by down-regulating cyclin/Cdk1 to arrest early cell cycles in Drosophila. Embryos that were arrested two cell cycles prior to the normal MBT activated widespread transcription of the zygotic genome including genes previously described as N/C dependent. Zygotic transcription of these genes largely retained features of their regulation in space and time. Furthermore, zygotically regulated post-MBT events such as cellularization and gastrulation movements occurred in these cell cycle-arrested embryos. These results are not compatible with models suggesting that these MBT events are directly coupled to N/C. Cyclin/Cdk1 activity normally declines in tight association with increasing N/C and is regulated by N/C. By experimentally promoting the decrease in cyclin/Cdk1, we uncoupled MBT from N/C increase, arguing that N/C-guided down-regulation of cyclin/Cdk1 is sufficient for genome activation and MBT.
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Affiliation(s)
- Isaac J. T. Strong
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Xiaoyun Lei
- Hunan Key Laboratory of Molecular Precision Medicine, Department of Oncology, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Fang Chen
- Hunan Key Laboratory of Molecular Precision Medicine, Department of Oncology, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Kai Yuan
- Hunan Key Laboratory of Molecular Precision Medicine, Department of Oncology, Xiangya Hospital, Central South University, Changsha, Hunan, China
- Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, China
| | - Patrick H. O’Farrell
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
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20
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Koromila T, Gao F, Iwasaki Y, He P, Pachter L, Gergen JP, Stathopoulos A. Odd-paired is a pioneer-like factor that coordinates with Zelda to control gene expression in embryos. eLife 2020; 9:e59610. [PMID: 32701060 PMCID: PMC7417190 DOI: 10.7554/elife.59610] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 07/22/2020] [Indexed: 01/29/2023] Open
Abstract
Pioneer factors such as Zelda (Zld) help initiate zygotic transcription in Drosophila early embryos, but whether other factors support this dynamic process is unclear. Odd-paired (Opa), a zinc-finger transcription factor expressed at cellularization, controls the transition of genes from pair-rule to segmental patterns along the anterior-posterior axis. Finding that Opa also regulates expression through enhancer sog_Distal along the dorso-ventral axis, we hypothesized Opa's role is more general. Chromatin-immunoprecipitation (ChIP-seq) confirmed its in vivo binding to sog_Distal but also identified widespread binding throughout the genome, comparable to Zld. Furthermore, chromatin assays (ATAC-seq) demonstrate that Opa, like Zld, influences chromatin accessibility genome-wide at cellularization, suggesting both are pioneer factors with common as well as distinct targets. Lastly, embryos lacking opa exhibit widespread, late patterning defects spanning both axes. Collectively, these data suggest Opa is a general timing factor and likely late-acting pioneer factor that drives a secondary wave of zygotic gene expression.
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Affiliation(s)
- Theodora Koromila
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - Fan Gao
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - Yasuno Iwasaki
- Stony Brook University, Department of Biochemistry and Cell Biology and Center for Developmental GeneticsStony BrookUnited States
| | - Peng He
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - Lior Pachter
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
| | - J Peter Gergen
- Stony Brook University, Department of Biochemistry and Cell Biology and Center for Developmental GeneticsStony BrookUnited States
| | - Angelike Stathopoulos
- California Institute of Technology, Division of Biology and Biological EngineeringPasadenaUnited States
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21
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Chan SH, Tang Y, Miao L, Darwich-Codore H, Vejnar CE, Beaudoin JD, Musaev D, Fernandez JP, Benitez MDJ, Bazzini AA, Moreno-Mateos MA, Giraldez AJ. Brd4 and P300 Confer Transcriptional Competency during Zygotic Genome Activation. Dev Cell 2020; 49:867-881.e8. [PMID: 31211993 DOI: 10.1016/j.devcel.2019.05.037] [Citation(s) in RCA: 67] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Revised: 01/10/2019] [Accepted: 05/21/2019] [Indexed: 12/28/2022]
Abstract
The awakening of the genome after fertilization is a cornerstone of animal development. However, the mechanisms that activate the silent genome after fertilization are poorly understood. Here, we show that transcriptional competency is regulated by Brd4- and P300-dependent histone acetylation in zebrafish. Live imaging of transcription revealed that genome activation, beginning at the miR-430 locus, is gradual and stochastic. We show that genome activation does not require slowdown of the cell cycle and is regulated through the translation of maternally inherited mRNAs. Among these, the enhancer regulators P300 and Brd4 can prematurely activate transcription and restore transcriptional competency when maternal mRNA translation is blocked, whereas inhibition of histone acetylation blocks genome activation. We conclude that P300 and Brd4 are sufficient to trigger genome-wide transcriptional competency by regulating histone acetylation on the first zygotic genes in zebrafish. This mechanism is critical for initiating zygotic development and developmental reprogramming.
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Affiliation(s)
- Shun Hang Chan
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Yin Tang
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Liyun Miao
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Hiba Darwich-Codore
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Charles E Vejnar
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Jean-Denis Beaudoin
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Damir Musaev
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Juan P Fernandez
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Maria D J Benitez
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Ariel A Bazzini
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA; Department of Molecular and Integrative Physiology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | | | - Antonio J Giraldez
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA; Stem Cell Center, Yale University School of Medicine, New Haven, CT 06510, USA; Yale Cancer Center, Yale University School of Medicine, New Haven, CT 06510, USA.
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22
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Expression Analysis of mRNA Decay of Maternal Genes during Bombyx mori Maternal-to-Zygotic Transition. Int J Mol Sci 2019; 20:ijms20225651. [PMID: 31718114 PMCID: PMC6887711 DOI: 10.3390/ijms20225651] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2019] [Revised: 11/06/2019] [Accepted: 11/06/2019] [Indexed: 11/24/2022] Open
Abstract
Maternal genes play an important role in the early embryonic development of the silkworm. Early embryonic development without new transcription depends on maternal components stored in the egg during oocyte maturation. The maternal-to-zygotic transition (MZT) is a tightly regulated process that includes maternal mRNAs elimination and zygotic transcription initiation. This process has been extensively studied within model species. Each model organism has a unique pattern of maternal transcriptional clearance classes in MZT. In this study, we identified 66 maternal genes through bioinformatics analysis and expression analysis in the eggs of silkworm virgin moths (Bombyx mori). All 66 maternal genes were expressed in vitellogenesis in day eight female pupae. During MZT, the degradation of maternal gene mRNAs could be divided into three clusters. We found that eight maternal genes of cluster 1 remained stable from 0 to 3.0 h, 17 maternal genes of cluster 2 were significantly decayed from 0.5 to 1.0 h and 41 maternal genes of cluster 3 were significantly decayed after 1.5 h. Therefore, the initial time-point of degradation of cluster 2 was earlier than that of cluster 3. The maternal gene mRNAs decay of clusters 2 and 3 is first initiated by maternal degradation activity. Our study expands upon the identification of silkworm maternal genes and provides a perspective for further research of the embryo development in Bombyx mori.
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23
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Chari S, Wilky H, Govindan J, Amodeo AA. Histone concentration regulates the cell cycle and transcription in early development. Development 2019; 146:dev.177402. [PMID: 31511251 DOI: 10.1242/dev.177402] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 08/28/2019] [Indexed: 12/12/2022]
Abstract
The early embryos of many animals, including flies, fish and frogs, have unusually rapid cell cycles and delayed onset of transcription. These divisions are dependent on maternally supplied RNAs and proteins including histones. Previous work suggests that the pool size of maternally provided histones can alter the timing of zygotic genome activation (ZGA) in frogs and fish. Here, we examine the effects of under- and overexpression of maternal histones in Drosophila embryogenesis. Decreasing histone concentration advances zygotic transcription, cell cycle elongation, Chk1 activation and gastrulation. Conversely, increasing histone concentration delays transcription and results in an additional nuclear cycle before gastrulation. Numerous zygotic transcripts are sensitive to histone concentration, and the promoters of histone-sensitive genes are associated with specific chromatin features linked to increased histone turnover. These include enrichment of the pioneer transcription factor Zelda, and lack of SIN3A and associated histone deacetylases. Our findings uncover a crucial regulatory role for histone concentrations in ZGA of Drosophila.
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Affiliation(s)
- Sudarshan Chari
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Henry Wilky
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Jayalakshmi Govindan
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Amanda A Amodeo
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
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24
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Abstract
Following fertilization, the two specified gametes must unite to create an entirely new organism. The genome is initially transcriptionally quiescent, allowing the zygote to be reprogrammed into a totipotent state. Gradually, the genome is activated through a process known as the maternal-to-zygotic transition, which enables zygotic gene products to replace the maternal supply that initiated development. This essential transition has been broadly characterized through decades of research in several model organisms. However, we still lack a full mechanistic understanding of how genome activation is executed and how this activation relates to the reprogramming of the zygotic chromatin architecture. Recent work highlights the central role of transcriptional activators and suggests that these factors may coordinate transcriptional activation with other developmental changes.
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25
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Gentsch GE, Owens NDL, Smith JC. The Spatiotemporal Control of Zygotic Genome Activation. iScience 2019; 16:485-498. [PMID: 31229896 PMCID: PMC6593175 DOI: 10.1016/j.isci.2019.06.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Revised: 03/07/2019] [Accepted: 06/06/2019] [Indexed: 11/16/2022] Open
Abstract
One of the earliest and most significant events in embryonic development is zygotic genome activation (ZGA). In several species, bulk transcription begins at the midblastula transition (MBT) when, after a certain number of cleavages, the embryo attains a particular nuclear-to-cytoplasmic (N/C) ratio, maternal repressors become sufficiently diluted, and the cell cycle slows down. Here we resolve the frog ZGA in time and space by profiling RNA polymerase II (RNAPII) engagement and its transcriptional readout. We detect a gradual increase in both the quantity and the length of RNAPII elongation before the MBT, revealing that >1,000 zygotic genes disregard the N/C timer for their activation and that the sizes of newly transcribed genes are not necessarily constrained by cell cycle duration. We also find that Wnt, Nodal, and BMP signaling together generate most of the spatiotemporal dynamics of regional ZGA, directing the formation of orthogonal body axes and proportionate germ layers.
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Affiliation(s)
- George E Gentsch
- Developmental Biology Laboratory, Francis Crick Institute, London NW1 1AT, UK.
| | - Nick D L Owens
- Department of Stem Cell and Developmental Biology, Pasteur Institute, Paris 75015, France
| | - James C Smith
- Developmental Biology Laboratory, Francis Crick Institute, London NW1 1AT, UK.
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26
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Chen H, Einstein LC, Little SC, Good MC. Spatiotemporal Patterning of Zygotic Genome Activation in a Model Vertebrate Embryo. Dev Cell 2019; 49:852-866.e7. [PMID: 31211992 PMCID: PMC6655562 DOI: 10.1016/j.devcel.2019.05.036] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 03/26/2019] [Accepted: 05/20/2019] [Indexed: 12/14/2022]
Abstract
A defining feature of early embryogenesis is the transition from maternal to zygotic control. This transition requires embryo-wide zygotic genome activation (ZGA), but the extent of spatiotemporal coordination of ZGA between individual cells is unknown. Multiple interrelated parameters, including elapsed time, completed cycles of cell division, and cell size may impact ZGA onset; however, the principal determinant of ZGA during vertebrate embryogenesis is debated. Here, we perform single-cell imaging of large-scale ZGA in whole-mount Xenopus embryos. We find a striking new spatiotemporal pattern of ZGA whose onset tightly correlates with cell size but not with elapsed time or number of cell divisions. Further, reducing cell size induces premature ZGA, dose dependently. We conclude that large-scale ZGA is not spatially uniform and that its onset is determined at the single-cell level, primarily by cell size. Our study suggests that spatial patterns of ZGA onset may be a common feature of embryonic systems.
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Affiliation(s)
- Hui Chen
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Lily C Einstein
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Shawn C Little
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Matthew C Good
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA.
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27
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Vastenhouw NL, Cao WX, Lipshitz HD. The maternal-to-zygotic transition revisited. Development 2019; 146:146/11/dev161471. [PMID: 31189646 DOI: 10.1242/dev.161471] [Citation(s) in RCA: 207] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The development of animal embryos is initially directed by maternal gene products. Then, during the maternal-to-zygotic transition (MZT), developmental control is handed to the zygotic genome. Extensive research in both vertebrate and invertebrate model organisms has revealed that the MZT can be subdivided into two phases, during which very different modes of gene regulation are implemented: initially, regulation is exclusively post-transcriptional and post-translational, following which gradual activation of the zygotic genome leads to predominance of transcriptional regulation. These changes in the gene expression program of embryos are precisely controlled and highly interconnected. Here, we review current understanding of the mechanisms that underlie handover of developmental control during the MZT.
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Affiliation(s)
- Nadine L Vastenhouw
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstraße 108, 01307 Dresden, Germany
| | - Wen Xi Cao
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, Ontario M5G 1M1, Canada
| | - Howard D Lipshitz
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, Ontario M5G 1M1, Canada
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28
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Initiation of the zygotic genetic program in the ascidian embryo. Semin Cell Dev Biol 2018; 84:111-117. [DOI: 10.1016/j.semcdb.2018.02.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 02/08/2018] [Accepted: 02/08/2018] [Indexed: 12/26/2022]
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29
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Hamm DC, Harrison MM. Regulatory principles governing the maternal-to-zygotic transition: insights from Drosophila melanogaster. Open Biol 2018; 8:180183. [PMID: 30977698 PMCID: PMC6303782 DOI: 10.1098/rsob.180183] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 11/09/2018] [Indexed: 12/19/2022] Open
Abstract
The onset of metazoan development requires that two terminally differentiated germ cells, a sperm and an oocyte, become reprogrammed to the totipotent embryo, which can subsequently give rise to all the cell types of the adult organism. In nearly all animals, maternal gene products regulate the initial events of embryogenesis while the zygotic genome remains transcriptionally silent. Developmental control is then passed from mother to zygote through a process known as the maternal-to-zygotic transition (MZT). The MZT comprises an intimately connected set of molecular events that mediate degradation of maternally deposited mRNAs and transcriptional activation of the zygotic genome. This essential developmental transition is conserved among metazoans but is perhaps best understood in the fruit fly, Drosophila melanogaster. In this article, we will review our understanding of the events that drive the MZT in Drosophila embryos and highlight parallel mechanisms driving this transition in other animals.
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Affiliation(s)
| | - Melissa M. Harrison
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA
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30
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Johnson MR, Stephenson RA, Ghaemmaghami S, Welte MA. Developmentally regulated H2Av buffering via dynamic sequestration to lipid droplets in Drosophila embryos. eLife 2018; 7:36021. [PMID: 30044219 PMCID: PMC6089599 DOI: 10.7554/elife.36021] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 07/24/2018] [Indexed: 12/23/2022] Open
Abstract
Regulating nuclear histone balance is essential for survival, yet in early Drosophila melanogaster embryos many regulatory strategies employed in somatic cells are unavailable. Previous work had suggested that lipid droplets (LDs) buffer nuclear accumulation of the histone variant H2Av. Here, we elucidate the buffering mechanism and demonstrate that it is developmentally controlled. Using live imaging, we find that H2Av continuously exchanges between LDs. Our data suggest that the major driving force for H2Av accumulation in nuclei is H2Av abundance in the cytoplasm and that LD binding slows nuclear import kinetically, by limiting this cytoplasmic pool. Nuclear H2Av accumulation is indeed inversely regulated by overall buffering capacity. Histone exchange between LDs abruptly ceases during the midblastula transition, presumably to allow canonical regulatory mechanisms to take over. These findings provide a mechanistic basis for the emerging role of LDs as regulators of protein homeostasis and demonstrate that LDs can control developmental progression.
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Affiliation(s)
| | | | - Sina Ghaemmaghami
- Department of Biology, University of Rochester, Rochester, United States
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31
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Seller CA, O’Farrell PH. Rif1 prolongs the embryonic S phase at the Drosophila mid-blastula transition. PLoS Biol 2018; 16:e2005687. [PMID: 29746464 PMCID: PMC5963817 DOI: 10.1371/journal.pbio.2005687] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 05/22/2018] [Accepted: 04/23/2018] [Indexed: 01/09/2023] Open
Abstract
In preparation for dramatic morphogenetic events of gastrulation, rapid embryonic cell cycles slow at the mid-blastula transition (MBT). In Drosophila melanogaster embryos, down-regulation of cyclin-dependent kinase 1 (Cdk1) activity initiates this slowing by delaying replication of heterochromatic satellite sequences and extending S phase. We found that Cdk1 activity inhibited the chromatin association of Rap1 interacting factor 1 (Rif1), a candidate repressor of replication. Furthermore, Rif1 bound selectively to satellite sequences following Cdk1 down-regulation at the MBT. In the next S phase, Rif1 dissociated from different satellites in an orderly schedule that anticipated their replication. Rif1 lacking potential phosphorylation sites failed to dissociate and dominantly prevented completion of replication. Loss of Rif1 in mutant embryos shortened the post-MBT S phase and rescued embryonic cell cycles disrupted by depletion of the S phase–promoting kinase, cell division cycle 7 (Cdc7). Our work shows that Rif1 and S phase kinases compose a replication timer controlling first the developmental onset of late replication and then the precise schedule of replication within S phase. In addition, we describe how onset of late replication fits into the progressive maturation of heterochromatin during development. Cells divide rapidly in the early embryos of most animals. However, during a conserved period of development known as the mid-blastula transition (MBT), the cell cycle slows down dramatically. In Drosophila embryos, genome duplication abruptly slows to initiate this cell cycle prolongation. This is achieved through the onset of late replication, a well-recognized phenomenon in which specific sequences of the genome await replication until long after other sequences have finished. Even though this temporal program of replication is a major determinant of the duration of S phase, the factors involved in this process remain unknown. Here, we use genetics and real-time microscopy to visualize replication in developing fly embryos and show that the protein Rap1 interacting factor 1 (Rif1) mediates the introduction of late replication at the MBT. We find that at this stage, Rif1 binds to and selectively delays the replication of large blocks of repetitive DNA known as satellite sequences. During the rapid cell cycles before the MBT, we show that the cyclin-dependent kinase 1 (Cdk1) prevents Rif1 from slowing down DNA replication by driving its removal from the chromatin. The developmental down-regulation of Cdk1 at the MBT allows Rif1 to associate with the satellite sequences and initiate cell cycle slowing. Our work provides new insights into the temporal programming of S phase and into the embryonic origin of late replication.
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Affiliation(s)
- Charles A. Seller
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Patrick H. O’Farrell
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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32
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Yu J, Guo X, Chen X, Qiao C, Chen B, Xie B, Luan X, Shen C, Zhu J, Liu J, Yan Y, He Z, Zheng B, Li H, Fang J. Activation of β-catenin causes defects in embryonic development during maternal-to-zygotic transition in mice. INTERNATIONAL JOURNAL OF CLINICAL AND EXPERIMENTAL PATHOLOGY 2018; 11:2514-2521. [PMID: 31938364 PMCID: PMC6958268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 03/15/2018] [Indexed: 06/10/2023]
Abstract
The early stage of embryogenesis is an important and complex cell-remodeling event in reproductive biology. To develop into a normal zygote, maternal-to-zygotic transition (MZT) is especially important for both zygotic genome activation (ZGA) and degradation of maternal products during the early stage of embryonic development. β-Catenin has been identified as an important regulator of embryonic development and adult stem cell division via the canonical Wnt/β-catenin signalling pathway. However, the role of activated β-catenin during MZT remains elusive. In the present study, we found that β-catenin is mainly expressed during embryogenesis in the cell membrane from the zygote- to morula-stage embryos but not in MII oocytes. To analyze the function of activated β-catenin during MZT, we conducted a β-catenin activation assay during embryogenesis. Our results indicated that development beyond the two-cell stage was inhibited in zygotes with β-catenin activation. Further analysis showed that activated form of β-catenin protein was increased and the phosphorylated form of β-catenin protein was decreased in culture embryos. Taken together, our study reveals that activation of β-catenin may play a vital role in zygotic development, determining the developmental potential of mouse embryos.
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Affiliation(s)
- Jun Yu
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
- Institute of Oncology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Xueke Guo
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Xia Chen
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Chen Qiao
- Department of Clinical Pharmacy, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Binghai Chen
- Department of Urology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Bing Xie
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
- Department of Obstetrics and Gynecology, The Fourth People’s Hospital of ZhenjiangZhenjiang, Jiangsu, China
| | - Xiaojin Luan
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Cong Shen
- Center for Reproduction and Genetics, Suzhou Municipal Hospital, The Affiliated Suzhou Hospital of Nanjing Medical UniversitySuzhou 215002, China
| | - Jiawei Zhu
- Center for Reproduction and Genetics, Suzhou Municipal Hospital, The Affiliated Suzhou Hospital of Nanjing Medical UniversitySuzhou 215002, China
| | - Jiajia Liu
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Yidan Yan
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
| | - Zeyu He
- Department of Clinical Medicine, China Medical UniversityShenyang, Liaoning, China
| | - Bo Zheng
- Center for Reproduction and Genetics, Suzhou Municipal Hospital, The Affiliated Suzhou Hospital of Nanjing Medical UniversitySuzhou 215002, China
| | - Hong Li
- Center for Reproduction and Genetics, Suzhou Municipal Hospital, The Affiliated Suzhou Hospital of Nanjing Medical UniversitySuzhou 215002, China
| | - Jie Fang
- Department of Gynecology, Affiliated Hospital of Jiangsu University, Jiangsu UniversityZhenjiang 212001, Jiangsu, China
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33
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Oda-Ishii I, Abe T, Satou Y. Dynamics of two key maternal factors that initiate zygotic regulatory programs in ascidian embryos. Dev Biol 2018; 437:50-59. [PMID: 29550363 DOI: 10.1016/j.ydbio.2018.03.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2018] [Revised: 03/12/2018] [Accepted: 03/12/2018] [Indexed: 12/21/2022]
Abstract
In animal embryos, transcription is repressed for a definite period of time after fertilization. In the embryo of the ascidian, Ciona intestinalis (type A; or Ciona robusta), transcription of regulatory genes is repressed before the 8- or 16-cell stages. This initial transcriptional quiescence is important to enable the establishment of initial differential gene expression patterns along the animal-vegetal axis by maternal factors, because the third cell division separates the animal and vegetal hemispheres into distinct blastomeres. Indeed, maternal transcription factors directly activate zygotic gene expression by the 16-cell stage; Tcf7/β-catenin activates genes in the vegetal hemisphere, and Gata.a activates genes in the animal hemisphere. In the present study, we revealed the dynamics of Gata.a and β-catenin, and expression profiles of their target genes precisely. β-catenin began to translocate into the nuclei at the 16-cell stage, and thus expression of β-catenin targets began at the 16-cell stage. Although Gata.a is abundantly present before the 8-cell stage, transcription of Gata.a targets was repressed at and before the 4-cell stage, and their expression began at the 8-cell stage. Transcription of the β-catenin targets may be repressed by the same mechanism in early embryos, because β-catenin targets were not expressed in 4-cell embryos treated with a GSK inhibitor, in which β-catenin translocated to the nuclei. Thus, these two maternal factors have different dynamics, which establish the pre-pattern for zygotic genetic programs in 16-cell embryos.
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Affiliation(s)
- Izumi Oda-Ishii
- Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Tetsuya Abe
- Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Yutaka Satou
- Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
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34
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Lefebvre FA, Lécuyer É. Flying the RNA Nest: Drosophila Reveals Novel Insights into the Transcriptome Dynamics of Early Development. J Dev Biol 2018; 6:jdb6010005. [PMID: 29615554 PMCID: PMC5875563 DOI: 10.3390/jdb6010005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 03/01/2018] [Accepted: 03/05/2018] [Indexed: 01/02/2023] Open
Abstract
Early development is punctuated by a series of pervasive and fast paced transitions. These events reshape a differentiated oocyte into a totipotent embryo and allow it to gradually mount a genetic program of its own, thereby framing a new organism. Specifically, developmental transitions that ensure the maternal to embryonic control of developmental events entail a deep remodeling of transcriptional and transcriptomic landscapes. Drosophila provides an elegant and genetically tractable system to investigate these conserved changes at a dazzling developmental pace. Here, we review recent studies applying emerging technologies such as ribosome profiling, in situ Hi-C chromatin probing and live embryo RNA imaging to investigate the transcriptional dynamics at play during Drosophila embryogenesis. In light of this new literature, we revisit the main models of zygotic genome activation (ZGA). We also review the contributions played by zygotic transcription in shaping embryogenesis and explore emerging concepts of processes such as transcriptional bursting and transcriptional memory.
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Affiliation(s)
- Fabio Alexis Lefebvre
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, QC H2W 1R7, Canada.
- Département de Biochimie, Université de Montréal, Montréal, QC H3T 1J4, Canada.
| | - Éric Lécuyer
- Institut de Recherches Cliniques de Montréal (IRCM), Montréal, QC H2W 1R7, Canada.
- Département de Biochimie, Université de Montréal, Montréal, QC H3T 1J4, Canada.
- Division of Experimental Medicine, McGill University, Montréal, QC H3A 0G4, Canada.
- IRCM, RNA Biology Laboratory, 110 Avenue des Pins, Ouest, Montréal, QC H2W 1R7, Canada.
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35
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Mitotic waves in the early embryogenesis of Drosophila: Bistability traded for speed. Proc Natl Acad Sci U S A 2018; 115:E2165-E2174. [PMID: 29449348 DOI: 10.1073/pnas.1714873115] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Early embryogenesis of most metazoans is characterized by rapid and synchronous cleavage divisions. Chemical waves of Cdk1 activity were previously shown to spread across Drosophila embryos, and the underlying molecular processes were dissected. Here, we present the theory of the physical mechanisms that control Cdk1 waves in Drosophila The in vivo dynamics of Cdk1 are captured by a transiently bistable reaction-diffusion model, where time-dependent reaction terms account for the growing level of cyclins and Cdk1 activation across the cell cycle. We identify two distinct regimes. The first one is observed in mutants of the mitotic switch. There, waves are triggered by the classical mechanism of a stable state invading a metastable one. Conversely, waves in wild type reflect a transient phase that preserves the Cdk1 spatial gradients while the overall level of Cdk1 activity is swept upward by the time-dependent reaction terms. This unique mechanism generates a wave-like spreading that differs from bistable waves for its dependence on dynamic parameters and its faster speed. Namely, the speed of "sweep" waves strikingly decreases as the strength of the reaction terms increases and scales as the powers 3/4, -1/2, and 7/12 of Cdk1 molecular diffusivity, noise amplitude, and rate of increase of Cdk1 activity in the cell-cycle S phase, respectively. Theoretical predictions are supported by numerical simulations and experiments that couple quantitative measurements of Cdk1 activity and genetic perturbations of the accumulation rate of cyclins. Finally, our analysis bears upon the inhibition required to suppress Cdk1 waves at the cell-cycle pause for the maternal-to-zygotic transition.
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36
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Abstract
The activation of the zygotic genome and onset of transcription in blastula embryos is linked to changes in cell behavior and remodeling of the cell cycle and constitutes a transition from exclusive maternal to zygotic control of development. This step in development is referred to as mid-blastula transition and has served as a paradigm for the link between developmental program and cell behavior and morphology. Here, we discuss the mechanism and functional relationships between the zygotic genome activation and cell cycle control during mid-blastula transition with a focus on Drosophila embryos.
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Affiliation(s)
- Boyang Liu
- Institute for Developmental Biochemistry, Medical School, University of Göttingen, Justus-von-Liebig-Weg11, Göttingen 37077, Germany
| | - Jörg Grosshans
- Institute for Developmental Biochemistry, Medical School, University of Göttingen, Justus-von-Liebig-Weg11, Göttingen 37077, Germany.
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37
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Jukam D, Shariati SAM, Skotheim JM. Zygotic Genome Activation in Vertebrates. Dev Cell 2017; 42:316-332. [PMID: 28829942 PMCID: PMC5714289 DOI: 10.1016/j.devcel.2017.07.026] [Citation(s) in RCA: 262] [Impact Index Per Article: 37.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 07/25/2017] [Accepted: 07/28/2017] [Indexed: 12/12/2022]
Abstract
The first major developmental transition in vertebrate embryos is the maternal-to-zygotic transition (MZT) when maternal mRNAs are degraded and zygotic transcription begins. During the MZT, the embryo takes charge of gene expression to control cell differentiation and further development. This spectacular organismal transition requires nuclear reprogramming and the initiation of RNAPII at thousands of promoters. Zygotic genome activation (ZGA) is mechanistically coordinated with other embryonic events, including changes in the cell cycle, chromatin state, and nuclear-to-cytoplasmic component ratios. Here, we review progress in understanding vertebrate ZGA dynamics in frogs, fish, mice, and humans to explore differences and emphasize common features.
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Affiliation(s)
- David Jukam
- Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - S Ali M Shariati
- Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - Jan M Skotheim
- Department of Biology, Stanford University, Stanford, CA 94305, USA.
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38
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Arsala D, Lynch JA. Ploidy has little effect on timing early embryonic events in the haplo-diploid wasp Nasonia. Genesis 2017; 55. [PMID: 28432826 DOI: 10.1002/dvg.23029] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Revised: 02/20/2017] [Accepted: 03/06/2017] [Indexed: 12/18/2022]
Abstract
The nucleocytoplasmic (N/C) ratio plays a prominent role in the maternal-to-zygotic transition (MZT) in many animals. The effect of the N/C ratio on cell-cycle lengthening and zygotic genome activation (ZGA) has been studied extensively in Drosophila, where haploid embryos experience an additional division prior to completing cellularization and triploid embryos cellularize precociously by one division. In this study, we set out to understand how the obligate difference in ploidy in the haplodiploid wasp, Nasonia, affects the MZT and which aspects of the Drosophila MZT are conserved. While subtle differences in early embryonic development were observed in comparisons among haploid, diploid, and triploid embryos, in all cases embryos cellularize at cell cycle 12. When ZGA was inhibited, both diploid female, and haploid male, embryos went through 12 syncytial divisions and failed to cellularize before dying without further divisions. We also found that key players of the Drosophila MZT are conserved in Nasonia but have novel expression patterns. Our results suggest that zygotically expressed genes have a reduced role in determining the timing of cellularization in Nasonia relative to Drosophila, and that a stronger reliance on a maternal timer is more compatible with species where variations in embryonic ploidy are obligatory.
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Affiliation(s)
- Deanna Arsala
- University of Illinois at Chicago, Chicago, Illinois
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39
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Joseph SR, Pálfy M, Hilbert L, Kumar M, Karschau J, Zaburdaev V, Shevchenko A, Vastenhouw NL. Competition between histone and transcription factor binding regulates the onset of transcription in zebrafish embryos. eLife 2017; 6. [PMID: 28425915 PMCID: PMC5451213 DOI: 10.7554/elife.23326] [Citation(s) in RCA: 90] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 04/19/2017] [Indexed: 01/09/2023] Open
Abstract
Upon fertilization, the genome of animal embryos remains transcriptionally inactive until the maternal-to-zygotic transition. At this time, the embryo takes control of its development and transcription begins. How the onset of zygotic transcription is regulated remains unclear. Here, we show that a dynamic competition for DNA binding between nucleosome-forming histones and transcription factors regulates zebrafish genome activation. Taking a quantitative approach, we found that the concentration of non-DNA-bound core histones sets the time for the onset of transcription. The reduction in nuclear histone concentration that coincides with genome activation does not affect nucleosome density on DNA, but allows transcription factors to compete successfully for DNA binding. In agreement with this, transcription factor binding is sensitive to histone levels and the concentration of transcription factors also affects the time of transcription. Our results demonstrate that the relative levels of histones and transcription factors regulate the onset of transcription in the embryo. DOI:http://dx.doi.org/10.7554/eLife.23326.001 The DNA in a fertilized egg contains all the information required to form an animal’s body. In order for the animal to develop properly, particular genes encoded in the DNA are only active at specific times. The DNA is wrapped around proteins called histones, which allows the DNA to be tightly packed inside the cell. However, histones can block other proteins called transcription factors from binding to the DNA to activate the genes. Young embryos initially develop with all of their genes switched off, relying on the nutrients and other molecules provided by their mother. After some time, the embryo starts to switch on its own genes to take control of its own development, but it was not clear how this happens. Joseph et al. investigated how genes are activated in zebrafish embryos, which are often used as models to study how animals develop. The experiments show that competition between histones and transcription factors for binding to DNA controls when genes are switched on. In young fish embryos, there are so many histones present that transcription factors have no opportunity to bind to DNA. Over time, however, the numbers of histones decrease, allowing transcription factors to bind to DNA and switch on genes. Histones and transcription factors regulate the activity of genes throughout the life of the animal. Therefore, competition between these two types of protein may also control gene activity in other situations. A better understanding of how gene activity is controlled could allow researchers to more easily grow different types of cell in the laboratory or to reprogram specific cells in the body. As such, these new findings may aid the development of therapies to regenerate organs or tissues that have been damaged by injury or disease. DOI:http://dx.doi.org/10.7554/eLife.23326.002
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Affiliation(s)
- Shai R Joseph
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Máté Pálfy
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Lennart Hilbert
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.,Center for Systems Biology Dresden, Dresden, Germany.,Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Mukesh Kumar
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Jens Karschau
- Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Vasily Zaburdaev
- Center for Systems Biology Dresden, Dresden, Germany.,Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
| | - Andrej Shevchenko
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Nadine L Vastenhouw
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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40
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Regulation of DNA Replication in Early Embryonic Cleavages. Genes (Basel) 2017; 8:genes8010042. [PMID: 28106858 PMCID: PMC5295036 DOI: 10.3390/genes8010042] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/06/2017] [Accepted: 01/11/2017] [Indexed: 11/18/2022] Open
Abstract
Early embryonic cleavages are characterized by short and highly synchronous cell cycles made of alternating S- and M-phases with virtually absent gap phases. In this contracted cell cycle, the duration of DNA synthesis can be extraordinarily short. Depending on the organism, the whole genome of an embryo is replicated at a speed that is between 20 to 60 times faster than that of a somatic cell. Because transcription in the early embryo is repressed, DNA synthesis relies on a large stockpile of maternally supplied proteins stored in the egg representing most, if not all, cellular genes. In addition, in early embryonic cell cycles, both replication and DNA damage checkpoints are inefficient. In this article, we will review current knowledge on how DNA synthesis is regulated in early embryos and discuss possible consequences of replicating chromosomes with little or no quality control.
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41
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Pálfy M, Joseph SR, Vastenhouw NL. The timing of zygotic genome activation. Curr Opin Genet Dev 2017; 43:53-60. [PMID: 28088031 DOI: 10.1016/j.gde.2016.12.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 12/01/2016] [Accepted: 12/02/2016] [Indexed: 12/20/2022]
Abstract
After fertilization, the embryonic genome is inactive until transcription is initiated during the maternal-to-zygotic transition. How the onset of transcription is regulated in a precisely timed manner, however, is a long standing question in biology. Several mechanisms have been shown to contribute to the temporal regulation of genome activation but none of them can fully explain the general absence of transcription as well the gene specific onset that follows. Here we review the work that has been done toward elucidating the mechanisms underlying the temporal regulation of transcription in embryos.
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Affiliation(s)
- Máté Pálfy
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Shai R Joseph
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Nadine L Vastenhouw
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.
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42
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Zhang M, Skirkanich J, Lampson MA, Klein PS. Cell Cycle Remodeling and Zygotic Gene Activation at the Midblastula Transition. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 953:441-487. [DOI: 10.1007/978-3-319-46095-6_9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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43
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Blythe SA, Wieschaus EF. Establishment and maintenance of heritable chromatin structure during early Drosophila embryogenesis. eLife 2016; 5:20148. [PMID: 27879204 PMCID: PMC5156528 DOI: 10.7554/elife.20148] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 11/21/2016] [Indexed: 12/18/2022] Open
Abstract
During embryogenesis, the initial chromatin state is established during a period of rapid proliferative activity. We have measured with 3-min time resolution how heritable patterns of chromatin structure are initially established and maintained during the midblastula transition (MBT). We find that regions of accessibility are established sequentially, where enhancers are opened in advance of promoters and insulators. These open states are stably maintained in highly condensed mitotic chromatin to ensure faithful inheritance of prior accessibility status across cell divisions. The temporal progression of establishment is controlled by the biological timers that control the onset of the MBT. In general, acquisition of promoter accessibility is controlled by the biological timer that measures the nucleo-cytoplasmic (N:C) ratio, whereas timing of enhancer accessibility is regulated independently of the N:C ratio. These different timing classes each associate with binding sites for two transcription factors, GAGA-factor and Zelda, previously implicated in controlling chromatin accessibility at ZGA. DOI:http://dx.doi.org/10.7554/eLife.20148.001
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Affiliation(s)
- Shelby A Blythe
- Howard Hughes Medical Institute, Princeton University, Princeton, United States
| | - Eric F Wieschaus
- Howard Hughes Medical Institute, Princeton University, Princeton, United States
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44
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Onichtchouk DV, Voronina AS. Regulation of Zygotic Genome and Cellular Pluripotency. BIOCHEMISTRY (MOSCOW) 2016; 80:1723-33. [PMID: 26878577 DOI: 10.1134/s0006297915130088] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Events, manifesting transition from maternal to zygotic period of development are studied for more than 100 years, but underlying mechanisms are not yet clear. We provide a brief historical overview of development of concepts and explain the specific terminology used in the field. We further discuss differences and similarities between the zygotic genome activation and in vitro reprogramming process. Finally, we envision the future research directions within the field, where biochemical methods will play increasingly important role.
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Affiliation(s)
- D V Onichtchouk
- University of Freiburg, Developmental Biology Unit, Biologie 1, Freiburg, 79194, Germany.
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45
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Clark E, Akam M. Odd-paired controls frequency doubling in Drosophila segmentation by altering the pair-rule gene regulatory network. eLife 2016; 5:e18215. [PMID: 27525481 PMCID: PMC5035143 DOI: 10.7554/elife.18215] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Accepted: 08/14/2016] [Indexed: 01/08/2023] Open
Abstract
The Drosophila embryo transiently exhibits a double-segment periodicity, defined by the expression of seven 'pair-rule' genes, each in a pattern of seven stripes. At gastrulation, interactions between the pair-rule genes lead to frequency doubling and the patterning of 14 parasegment boundaries. In contrast to earlier stages of Drosophila anteroposterior patterning, this transition is not well understood. By carefully analysing the spatiotemporal dynamics of pair-rule gene expression, we demonstrate that frequency-doubling is precipitated by multiple coordinated changes to the network of regulatory interactions between the pair-rule genes. We identify the broadly expressed but temporally patterned transcription factor, Odd-paired (Opa/Zic), as the cause of these changes, and show that the patterning of the even-numbered parasegment boundaries relies on Opa-dependent regulatory interactions. Our findings indicate that the pair-rule gene regulatory network has a temporally modulated topology, permitting the pair-rule genes to play stage-specific patterning roles.
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Affiliation(s)
- Erik Clark
- Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - Michael Akam
- Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Cambridge, United Kingdom
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Xie S, Mason FM, Martin AC. Loss of Gα12/13 exacerbates apical area dependence of actomyosin contractility. Mol Biol Cell 2016; 27:3526-3536. [PMID: 27489340 PMCID: PMC5221585 DOI: 10.1091/mbc.e16-05-0305] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 07/27/2016] [Indexed: 01/23/2023] Open
Abstract
Gα12/13 loss causes cells with a larger apical area to constrict later than smaller cells, leading to uncoordinated constriction. Apical area influences actin density, myosin regulation, and E-cadherin levels. Thus Gα12/13 is crucial for the robust initiation of contraction in a tissue in which cells initially have heterogeneous apical areas. During development, coordinated cell shape changes alter tissue shape. In the Drosophila ventral furrow and other epithelia, apical constriction of hundreds of epithelial cells folds the tissue. Genes in the Gα12/13 pathway coordinate collective apical constriction, but the mechanism of coordination is poorly understood. Coupling live-cell imaging with a computational approach to identify contractile events, we discovered that differences in constriction behavior are biased by initial cell shape. Disrupting Gα12/13 exacerbates this relationship. Larger apical area is associated with delayed initiation of contractile pulses, lower apical E-cadherin and F-actin levels, and aberrantly mobile Rho-kinase structures. Our results suggest that loss of Gα12/13 disrupts apical actin cortex organization and pulse initiation in a size-dependent manner. We propose that Gα12/13 robustly organizes the apical cortex despite variation in apical area to ensure the timely initiation of contractile pulses in a tissue with heterogeneity in starting cell shape.
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Affiliation(s)
- Shicong Xie
- Computational and Systems Biology Program, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Frank M Mason
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Adam C Martin
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
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47
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Sysoev VO, Fischer B, Frese CK, Gupta I, Krijgsveld J, Hentze MW, Castello A, Ephrussi A. Global changes of the RNA-bound proteome during the maternal-to-zygotic transition in Drosophila. Nat Commun 2016; 7:12128. [PMID: 27378189 PMCID: PMC4935972 DOI: 10.1038/ncomms12128] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 06/03/2016] [Indexed: 12/15/2022] Open
Abstract
The maternal-to-zygotic transition (MZT) is a process that occurs in animal embryos at the earliest developmental stages, during which maternally deposited mRNAs and other molecules are degraded and replaced by products of the zygotic genome. The zygotic genome is not activated immediately upon fertilization, and in the pre-MZT embryo post-transcriptional control by RNA-binding proteins (RBPs) orchestrates the first steps of development. To identify relevant Drosophila RBPs organism-wide, we refined the RNA interactome capture method for comparative analysis of the pre- and post-MZT embryos. We determine 523 proteins as high-confidence RBPs, half of which were not previously reported to bind RNA. Comparison of the RNA interactomes of pre- and post-MZT embryos reveals high dynamicity of the RNA-bound proteome during early development, and suggests active regulation of RNA binding of some RBPs. This resource provides unprecedented insight into the system of RBPs that govern the earliest steps of Drosophila development.
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Affiliation(s)
- Vasiliy O. Sysoev
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Bernd Fischer
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
- German Cancer Research Center, Im Neuenheimer Feld 580, 69120 Heidelberg, Germany
| | - Christian K. Frese
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Ishaan Gupta
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Jeroen Krijgsveld
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Matthias W. Hentze
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Alfredo Castello
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, England
| | - Anne Ephrussi
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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48
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Wragg J, Müller F. Transcriptional Regulation During Zygotic Genome Activation in Zebrafish and Other Anamniote Embryos. ADVANCES IN GENETICS 2016; 95:161-94. [PMID: 27503357 DOI: 10.1016/bs.adgen.2016.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Embryo development commences with the fusion of two terminally differentiated haploid gametes into the totipotent fertilized egg, which through a series of major cellular and molecular transitions generate a pluripotent cell mass. The activation of the zygotic genome occurs during the so-called maternal to zygotic transition and prepares the embryo for zygotic takeover from maternal factors, in the control of the development of cellular lineages during differentiation. Recent advances in next generation sequencing technologies have allowed the dissection of the genomic and epigenomic processes mediating this transition. These processes include reorganization of the chromatin structure to a transcriptionally permissive state, changes in composition and function of structural and regulatory DNA-binding proteins, and changeover of the transcriptome as it is overhauled from that deposited by the mother in the oocyte to a zygotically transcribed complement. Zygotic genome activation in zebrafish occurs 10 cell cycles after fertilization and provides an ideal experimental platform for elucidating the temporal sequence and dynamics of establishment of a transcriptionally active chromatin state and helps in identifying the determinants of transcription activation at polymerase II transcribed gene promoters. The relatively large number of pluripotent cells generated by the fast cell divisions before zygotic transcription provides sufficient biomass for next generation sequencing technology approaches to establish the temporal dynamics of events and suggest causative relationship between them. However, genomic and genetic technologies need to be improved further to capture the earliest events in development, where cell number is a limiting factor. These technologies need to be complemented with precise, inducible genetic interference studies using the latest genome editing tools to reveal the function of candidate determinants and to confirm the predictions made by classic embryological tools and genome-wide assays. In this review we summarize recent advances in the characterization of epigenetic regulation, transcription control, and gene promoter function during zygotic genome activation and how they fit with old models for the mechanisms of the maternal to zygotic transition. This review will focus on the zebrafish embryo but draw comparisons with other vertebrate model systems and refer to invertebrate models where informative.
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Affiliation(s)
- J Wragg
- University of Birmingham, Birmingham, United Kingdom
| | - F Müller
- University of Birmingham, Birmingham, United Kingdom
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Ferree PL, Deneke VE, Di Talia S. Measuring time during early embryonic development. Semin Cell Dev Biol 2016; 55:80-8. [PMID: 26994526 PMCID: PMC4903905 DOI: 10.1016/j.semcdb.2016.03.013] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 03/15/2016] [Indexed: 11/27/2022]
Abstract
In most metazoans, embryonic development is orchestrated by a precise series of cellular behaviors. Understanding how such events are regulated to achieve a stereotypical temporal progression is a fundamental problem in developmental biology. In this review, we argue that studying the regulation of the cell cycle in early embryonic development will reveal novel principles of how embryos accurately measure time. We will discuss the strategies that have emerged from studying early development of Drosophila embryos. By comparing the development of flies to that of other metazoans, we will highlight both conserved and alternative mechanisms to generate precision during embryonic development.
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Affiliation(s)
- Patrick L Ferree
- Department of Cell Biology, Duke University Medical Center, Durham NC, United States
| | - Victoria E Deneke
- Department of Cell Biology, Duke University Medical Center, Durham NC, United States
| | - Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham NC, United States.
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50
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Yuan K, Seller CA, Shermoen AW, O'Farrell PH. Timing the Drosophila Mid-Blastula Transition: A Cell Cycle-Centered View. Trends Genet 2016; 32:496-507. [PMID: 27339317 DOI: 10.1016/j.tig.2016.05.006] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2016] [Revised: 05/19/2016] [Accepted: 05/23/2016] [Indexed: 11/18/2022]
Abstract
At the mid-blastula transition (MBT), externally developing embryos refocus from increasing cell number to elaboration of the body plan. Studies in Drosophila reveal a sequence of changes in regulators of Cyclin:Cdk1 that increasingly restricts the activity of this cell cycle kinase to slow cell cycles during early embryogenesis. By reviewing these events, we provide an outline of the mechanisms slowing the cell cycle at and around the time of MBT. The perspectives developed should provide a guiding paradigm for the study of other MBT changes as the embryo transits from maternal control to a regulatory program centered on the expression of zygotic genes.
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Affiliation(s)
- Kai Yuan
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA
| | - Charles A Seller
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA
| | - Antony W Shermoen
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA
| | - Patrick H O'Farrell
- Department of Biophysics and Biochemistry, University of California San Francisco (UCSF), San Francisco, CA 94158, USA.
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