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Kojima ML, Hoppe C, Giraldez AJ. The maternal-to-zygotic transition: reprogramming of the cytoplasm and nucleus. Nat Rev Genet 2025; 26:245-267. [PMID: 39587307 PMCID: PMC11928286 DOI: 10.1038/s41576-024-00792-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/08/2024] [Indexed: 11/27/2024]
Abstract
A fertilized egg is initially transcriptionally silent and relies on maternally provided factors to initiate development. For embryonic development to proceed, the oocyte-inherited cytoplasm and the nuclear chromatin need to be reprogrammed to create a permissive environment for zygotic genome activation (ZGA). During this maternal-to-zygotic transition (MZT), which is conserved in metazoans, transient totipotency is induced and zygotic transcription is initiated to form the blueprint for future development. Recent technological advances have enhanced our understanding of MZT regulation, revealing common themes across species and leading to new fundamental insights about transcription, mRNA decay and translation.
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Affiliation(s)
- Mina L Kojima
- Department of Genetics, Yale University School of Medicine, New Haven, CT, USA
| | - Caroline Hoppe
- Department of Genetics, Yale University School of Medicine, New Haven, CT, USA
| | - Antonio J Giraldez
- Department of Genetics, Yale University School of Medicine, New Haven, CT, USA.
- Yale Stem Cell Center, Yale University School of Medicine, New Haven, CT, USA.
- Yale Cancer Center, Yale University School of Medicine, New Haven, CT, USA.
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2
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Di Talia S. Developmental Control of Cell Cycle and Signaling. Cold Spring Harb Perspect Biol 2025; 17:a041499. [PMID: 38858070 PMCID: PMC11864111 DOI: 10.1101/cshperspect.a041499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2024]
Abstract
In most species, the earliest stages of embryogenesis are characterized by rapid proliferation, which must be tightly controlled with other cellular processes across the large scale of the embryo. The study of this coordination has recently revealed new mechanisms of regulation of morphogenesis. Here, I discuss progress on how the integration of biochemical and mechanical signals leads to the proper positioning of cellular components, how signaling waves ensure the synchronization of the cell cycle, and how cell cycle transitions are properly timed. Similar concepts are emerging in the control of morphogenesis of other tissues, highlighting both common and unique features of early embryogenesis.
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Affiliation(s)
- Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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3
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Kukreja K, Jia BZ, McGeary SE, Patel N, Megason SG, Klein AM. Cell state transitions are decoupled from cell division during early embryo development. Nat Cell Biol 2024; 26:2035-2045. [PMID: 39516639 DOI: 10.1038/s41556-024-01546-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Accepted: 09/23/2024] [Indexed: 11/16/2024]
Abstract
As tissues develop, cells divide and differentiate concurrently. Conflicting evidence shows that cell division is either dispensable or required for formation of cell types. Here, to determine the role of cell division in differentiation, we arrested the cell cycle in zebrafish embryos using two independent approaches and profiled them at single-cell resolution. We show that cell division is dispensable for differentiation of all embryonic tissues from early gastrulation to the end of segmentation. However, arresting cell division does slow down differentiation in some cell types, and it induces global stress responses. While differentiation is robust to blocking cell division, the proportions of cells across cell states are not, but show evidence of partial compensation. This work clarifies our understanding of the role of cell division in development and showcases the utility of combining embryo-wide perturbations with single-cell RNA sequencing to uncover the role of common biological processes across multiple tissues.
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Affiliation(s)
- Kalki Kukreja
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
- Department of Chemistry, University of Chicago, Chicago, IL, USA
| | - Bill Z Jia
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
| | - Sean E McGeary
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Nikit Patel
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
- Department of Biomedical Engineering, Boston University, Boston, MA, USA
| | - Sean G Megason
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Allon M Klein
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA.
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4
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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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5
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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 53706 USA
| | - Audrey J Marsh
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI 53706 USA
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6
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Cho CY, Seller CA, O’Farrell PH. Temporal control of late replication and coordination of origin firing by self-stabilizing Rif1-PP1 hubs in Drosophila. Proc Natl Acad Sci U S A 2022; 119:e2200780119. [PMID: 35733247 PMCID: PMC9245680 DOI: 10.1073/pnas.2200780119] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Accepted: 05/19/2022] [Indexed: 12/25/2022] Open
Abstract
In the metazoan S phase, coordinated firing of clusters of origins replicates different parts of the genome in a temporal program. Despite advances, neither the mechanism controlling timing nor that coordinating firing of multiple origins is fully understood. Rif1, an evolutionarily conserved inhibitor of DNA replication, recruits protein phosphatase 1 (PP1) and counteracts firing of origins by S-phase kinases. During the midblastula transition (MBT) in Drosophila embryos, Rif1 forms subnuclear hubs at each of the large blocks of satellite sequences and delays their replication. Each Rif1 hub disperses abruptly just prior to the replication of the associated satellite sequences. Here, we show that the level of activity of the S-phase kinase, DDK, accelerated this dispersal program, and that the level of Rif1-recruited PP1 retarded it. Further, Rif1-recruited PP1 supported chromatin association of nearby Rif1. This influence of nearby Rif1 can create a "community effect" counteracting kinase-induced dissociation such that an entire hub of Rif1 undergoes switch-like dispersal at characteristic times that shift in response to the balance of Rif1-PP1 and DDK activities. We propose a model in which the spatiotemporal program of late replication in the MBT embryo is controlled by self-stabilizing Rif1-PP1 hubs, whose abrupt dispersal synchronizes firing of associated late origins.
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Affiliation(s)
- Chun-Yi Cho
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158
| | - Charles A. Seller
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158
| | - Patrick H. O’Farrell
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158
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7
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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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8
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Abstract
Understanding the mechanisms of embryonic cell cycles is a central goal of developmental biology, as the regulation of the cell cycle must be closely coordinated with other events during early embryogenesis. Quantitative imaging approaches have recently begun to reveal how the cell cycle oscillator is controlled in space and time, and how it is integrated with mechanical signals to drive morphogenesis. Here, we discuss how the Drosophila embryo has served as an excellent model for addressing the molecular and physical mechanisms of embryonic cell cycles, with comparisons to other model systems to highlight conserved and species-specific mechanisms. We describe how the rapid cleavage divisions characteristic of most metazoan embryos require chemical waves and cytoplasmic flows to coordinate morphogenesis across the large expanse of the embryo. We also outline how, in the late cleavage divisions, the cell cycle is inter-regulated with the activation of gene expression to ensure a reliable maternal-to-zygotic transition. Finally, we discuss how precise transcriptional regulation of the timing of mitosis ensures that tissue morphogenesis and cell proliferation are tightly controlled during gastrulation.
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Affiliation(s)
| | - Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27705, USA
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9
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Li F, Lo TY, Miles L, Wang Q, Noristani HN, Li D, Niu J, Trombley S, Goldshteyn JI, Wang C, Wang S, Qiu J, Pogoda K, Mandal K, Brewster M, Rompolas P, He Y, Janmey PA, Thomas GM, Li S, Song Y. The Atr-Chek1 pathway inhibits axon regeneration in response to Piezo-dependent mechanosensation. Nat Commun 2021; 12:3845. [PMID: 34158506 PMCID: PMC8219705 DOI: 10.1038/s41467-021-24131-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 05/25/2021] [Indexed: 02/05/2023] Open
Abstract
Atr is a serine/threonine kinase, known to sense single-stranded DNA breaks and activate the DNA damage checkpoint by phosphorylating Chek1, which inhibits Cdc25, causing cell cycle arrest. This pathway has not been implicated in neuroregeneration. We show that in Drosophila sensory neurons removing Atr or Chek1, or overexpressing Cdc25 promotes regeneration, whereas Atr or Chek1 overexpression, or Cdc25 knockdown impedes regeneration. Inhibiting the Atr-associated checkpoint complex in neurons promotes regeneration and improves synapse/behavioral recovery after CNS injury. Independent of DNA damage, Atr responds to the mechanical stimulus elicited during regeneration, via the mechanosensitive ion channel Piezo and its downstream NO signaling. Sensory neuron-specific knockout of Atr in adult mice, or pharmacological inhibition of Atr-Chek1 in mammalian neurons in vitro and in flies in vivo enhances regeneration. Our findings reveal the Piezo-Atr-Chek1-Cdc25 axis as an evolutionarily conserved inhibitory mechanism for regeneration, and identify potential therapeutic targets for treating nervous system trauma.
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Affiliation(s)
- Feng Li
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Tsz Y Lo
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Leann Miles
- The Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania, Philadelphia, PA, USA
| | - Qin Wang
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Harun N Noristani
- Shriners Hospitals Pediatric Research Center (Center for Neurorehabilitation and Neural Repair), Temple University School of Medicine, Philadelphia, PA, USA
- Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA, USA
| | - Dan Li
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Jingwen Niu
- Shriners Hospitals Pediatric Research Center (Center for Neurorehabilitation and Neural Repair), Temple University School of Medicine, Philadelphia, PA, USA
| | - Shannon Trombley
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Jessica I Goldshteyn
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Chuxi Wang
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Shuchao Wang
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Jingyun Qiu
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Katarzyna Pogoda
- Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA, USA
- Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland
| | - Kalpana Mandal
- Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Megan Brewster
- Department of Dermatology, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Ye He
- The City University of New York, Graduate Center - Advanced Science Research Center, Neuroscience Initiative, New York, NY, USA
| | - Paul A Janmey
- Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Gareth M Thomas
- Shriners Hospitals Pediatric Research Center (Center for Neurorehabilitation and Neural Repair), Temple University School of Medicine, Philadelphia, PA, USA
- Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA, USA
| | - Shuxin Li
- Shriners Hospitals Pediatric Research Center (Center for Neurorehabilitation and Neural Repair), Temple University School of Medicine, Philadelphia, PA, USA
- Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA, USA
| | - Yuanquan Song
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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10
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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: 5] [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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11
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Modeling the role for nuclear import dynamics in the early embryonic cell cycle. Biophys J 2021; 120:4277-4286. [PMID: 34022240 DOI: 10.1016/j.bpj.2021.05.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 04/22/2021] [Accepted: 05/06/2021] [Indexed: 11/21/2022] Open
Abstract
Nuclear composition determines nuclear function. The early embryos of many species begin life with large pools of maternally provided components that become rapidly imported into an increasing number of nuclei as the cells undergo repeated cleavage divisions. Because early cell cycles are too fast for nuclei to achieve steady-state nucleocytoplasmic partitioning, the composition of cleavage stage nuclei is likely dominated by nuclear import. The end of the rapid cleavage stage and onset of major zygotic transcription, known as the mid-blastula transition (MBT), is controlled by the ratio of nuclei/cytoplasm, indicating that changes in nuclear composition likely mediate MBT timing. Here, we explore how different nuclear import regimes can affect protein accumulation in the nucleus in the early Drosophila embryo. We find that nuclear import differs dramatically for a general nuclear cargo (NLS (nuclear localization signal)-mRFP) and a proposed MBT regulator (histone H3). We show that nuclear import rates of NLS-mRFP in a given nucleus remain relatively unchanged throughout the cleavage cycles, whereas those of H3 halve with each cycle. We model these two distinct modes of nuclear import as "nucleus-limited" and "import-limited" and examine how the two different modes can contribute to different protein accumulation dynamics. Finally, we incorporate these distinct modes of nuclear import into a model for cell-cycle regulation at the MBT and find that the import-limited H3 dynamics contribute to increased robustness and allow for stepwise cell-cycle slowing at the MBT.
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12
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Cao WX, Kabelitz S, Gupta M, Yeung E, Lin S, Rammelt C, Ihling C, Pekovic F, Low TCH, Siddiqui NU, Cheng MHK, Angers S, Smibert CA, Wühr M, Wahle E, Lipshitz HD. Precise Temporal Regulation of Post-transcriptional Repressors Is Required for an Orderly Drosophila Maternal-to-Zygotic Transition. Cell Rep 2021; 31:107783. [PMID: 32579915 PMCID: PMC7372737 DOI: 10.1016/j.celrep.2020.107783] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/06/2020] [Accepted: 05/28/2020] [Indexed: 12/12/2022] Open
Abstract
In animal embryos, the maternal-to-zygotic transition (MZT) hands developmental control from maternal to zygotic gene products. We show that the maternal proteome represents more than half of the protein-coding capacity of Drosophila melanogaster’s genome, and that 2% of this proteome is rapidly degraded during the MZT. Cleared proteins include the post-transcriptional repressors Cup, Trailer hitch (TRAL), Maternal expression at 31B (ME31B), and Smaug (SMG). Although the ubiquitin-proteasome system is necessary for clearance of these repressors, distinct E3 ligase complexes target them: the C-terminal to Lis1 Homology (CTLH) complex targets Cup, TRAL, and ME31B for degradation early in the MZT and the Skp/Cullin/F-box-containing (SCF) complex targets SMG at the end of the MZT. Deleting the C-terminal 233 amino acids of SMG abrogates F-box protein interaction and confers immunity to degradation. Persistent SMG downregulates zygotic re-expression of mRNAs whose maternal contribution is degraded by SMG. Thus, clearance of SMG permits an orderly MZT. Cao et al. show that 2% of the proteome is degraded in early Drosophila embryos, including a repressive ribonucleoprotein complex. Two E3 ubiquitin ligases separately act on distinct components of this complex to phase their clearance. Failure to degrade a key component, the Smaug RNA-binding protein, disrupts an orderly maternal-to-zygotic transition.
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Affiliation(s)
- Wen Xi Cao
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada
| | - Sarah Kabelitz
- Institute of Biochemistry and Biotechnology and Charles Tanford Protein Center, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06099 Halle, Germany
| | - Meera Gupta
- Department of Molecular Biology and the Lewis-Sigler Institute, Princeton University, Washington Road, Princeton, NJ 08544, USA
| | - Eyan Yeung
- Department of Molecular Biology and the Lewis-Sigler Institute, Princeton University, Washington Road, Princeton, NJ 08544, USA
| | - Sichun Lin
- Department of Pharmaceutical Sciences, University of Toronto, 144 College Street, Toronto, ON M5S 3M2, Canada
| | - Christiane Rammelt
- Institute of Biochemistry and Biotechnology and Charles Tanford Protein Center, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06099 Halle, Germany
| | - Christian Ihling
- Institute of Pharmacy and Charles Tanford Protein Center, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06099 Halle, Germany
| | - Filip Pekovic
- Institute of Biochemistry and Biotechnology and Charles Tanford Protein Center, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06099 Halle, Germany
| | - Timothy C H Low
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada
| | - Najeeb U Siddiqui
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada
| | - Matthew H K Cheng
- Department of Biochemistry, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada
| | - Stephane Angers
- Department of Pharmaceutical Sciences, University of Toronto, 144 College Street, Toronto, ON M5S 3M2, Canada; Department of Biochemistry, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada
| | - Craig A Smibert
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada; Department of Biochemistry, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada
| | - Martin Wühr
- Department of Molecular Biology and the Lewis-Sigler Institute, Princeton University, Washington Road, Princeton, NJ 08544, USA
| | - Elmar Wahle
- Institute of Biochemistry and Biotechnology and Charles Tanford Protein Center, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06099 Halle, Germany.
| | - Howard D Lipshitz
- Department of Molecular Genetics, University of Toronto, 661 University Avenue, Toronto, ON M5G 1M1, Canada.
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13
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Shindo Y, Amodeo AA. Excess histone H3 is a competitive Chk1 inhibitor that controls cell-cycle remodeling in the early Drosophila embryo. Curr Biol 2021; 31:2633-2642.e6. [PMID: 33848457 DOI: 10.1016/j.cub.2021.03.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 02/08/2021] [Accepted: 03/10/2021] [Indexed: 12/31/2022]
Abstract
The DNA damage checkpoint is crucial to protect genome integrity.1,2 However, the early embryos of many metazoans sacrifice this safeguard to allow for rapid cleavage divisions that are required for speedy development. At the mid-blastula transition (MBT), embryos switch from rapid cleavage divisions to slower, patterned divisions with the addition of gap phases and acquisition of DNA damage checkpoints. The timing of the MBT is dependent on the nuclear-to-cytoplasmic (N/C ratio)3-7 and the activation of the checkpoint kinase, Chk1.8-17 How Chk1 activity is coupled to the N/C ratio has remained poorly understood. Here, we show that dynamic changes in histone H3 availability in response to the increasing N/C ratio control Chk1 activity and thus time the MBT in the Drosophila embryo. We show that excess H3 in the early cycles interferes with cell-cycle slowing independent of chromatin incorporation. We find that the N-terminal tail of H3 acts as a competitive inhibitor of Chk1 in vitro and reduces Chk1 activity in vivo. Using a H3-tail mutant that has reduced Chk1 inhibitor activity, we show that the amount of available Chk1 sites in the H3 pool controls the dynamics of cell-cycle progression. Mathematical modeling quantitatively supports a mechanism where titration of H3 during early cleavage cycles regulates Chk1-dependent cell-cycle slowing. This study defines Chk1 regulation by H3 as a key mechanism that coordinates cell-cycle remodeling with developmental progression.
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Affiliation(s)
- Yuki Shindo
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA
| | - Amanda A Amodeo
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA; Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
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14
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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: 27] [Impact Index Per Article: 6.8] [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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15
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Control of Cell Growth and Proliferation by the Tribbles Pseudokinase: Lessons from Drosophila. Cancers (Basel) 2021; 13:cancers13040883. [PMID: 33672471 PMCID: PMC7923445 DOI: 10.3390/cancers13040883] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 02/09/2021] [Accepted: 02/14/2021] [Indexed: 12/13/2022] Open
Abstract
Simple Summary Tribbles pseudokinases represent a sub-branch of the CAMK (Ca2+/calmodulin-dependent protein kinase) subfamily and are associated with disease-associated signaling pathways associated with various cancers, including melanoma, lung, liver, and acute leukemia. The ability of this class of molecules to regulate cell proliferation was first recognized in the model organism Drosophila and the fruit fly genetic model and continues to provide insight into the molecular mechanism by which this family of adapter molecules regulates both normal development and disease associated with corruption of their proper regulation and function. Abstract The Tribbles (Trib) family of pseudokinase proteins regulate cell growth, proliferation, and differentiation during normal development and in response to environmental stress. Mutations in human Trib isoforms (Trib1, 2, and 3) have been associated with metabolic disease and linked to leukemia and the formation of solid tumors, including melanomas, hepatomas, and lung cancers. Drosophila Tribbles (Trbl) was the first identified member of this sub-family of pseudokinases and shares a conserved structure and similar functions to bind and direct the degradation of key mediators of cell growth and proliferation. Common Trib targets include Akt kinase (also known as protein kinase B), C/EBP (CAAT/enhancer binding protein) transcription factors, and Cdc25 phosphatases, leading to the notion that Trib family members stand athwart multiple pathways modulating their growth-promoting activities. Recent work using the Drosophila model has provided important insights into novel facets of conserved Tribbles functions in stem cell quiescence, tissue regeneration, metabolism connected to insulin signaling, and tumor formation linked to the Hippo signaling pathway. Here we highlight some of these recent studies and discuss their implications for understanding the complex roles Tribs play in cancers and disease pathologies.
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16
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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: 22] [Impact Index Per Article: 4.4] [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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17
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Liu B, Gregor I, Müller HA, Großhans J. Fluorescence fluctuation analysis reveals PpV dependent Cdc25 protein dynamics in living embryos. PLoS Genet 2020; 16:e1008735. [PMID: 32251417 PMCID: PMC7162543 DOI: 10.1371/journal.pgen.1008735] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Revised: 04/16/2020] [Accepted: 03/25/2020] [Indexed: 12/21/2022] Open
Abstract
The protein phosphatase Cdc25 is a key regulator of the cell cycle by activating Cdk-cyclin complexes. Cdc25 is regulated by its expression levels and post-translational mechanisms. In early Drosophila embryogenesis, Cdc25/Twine drives the fast and synchronous nuclear cycles. A pause in the cell cycle and the remodeling to a more generic cell cycle mode with a gap phase are determined by Twine inactivation and destruction in early interphase 14, in response to zygotic genome activation. Although the pseudokinase Tribbles contributes to the timely degradation of Twine, Twine levels are controlled by additional yet unknown post-translational mechanisms. Here, we apply a non-invasive method based on fluorescence fluctuation analysis (FFA) to record the absolute concentration profiles of Twine with minute-scale resolution in single living embryos. Employing this assay, we found that Protein phosphatase V (PpV), the homologue of the catalytic subunit of human PP6, ensures appropriately low Twine protein levels at the onset of interphase 14. PpV controls directly or indirectly the phosphorylation of Twine at multiple serine and threonine residues as revealed by phosphosite mapping. Mutational analysis confirmed that these sites are involved in control of Twine protein dynamics, and cell cycle remodeling is delayed in a fraction of the phosphosite mutant embryos. Our data reveal a novel mechanism for control of Twine protein levels and their significance for embryonic cell cycle remodeling.
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Affiliation(s)
- Boyang Liu
- Fachbereich Biologie (FB17), Philipps-Universität Marburg, Marburg, Germany
- Institut für Entwicklungsbiochemie, Universitätsmedizin, Georg-August-Universität Göttingen, Göttingen, Germany
| | - Ingo Gregor
- Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany
| | - H.-Arno Müller
- Fachgebiet Entwicklungsgenetik, Institut für Biologie, Universität Kassel, Kassel, Germany
| | - Jörg Großhans
- Fachbereich Biologie (FB17), Philipps-Universität Marburg, Marburg, Germany
- Institut für Entwicklungsbiochemie, Universitätsmedizin, Georg-August-Universität Göttingen, Göttingen, Germany
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18
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Multiple Functions of the Essential Gene PpV in Drosophila Early Development. G3-GENES GENOMES GENETICS 2019; 9:3583-3593. [PMID: 31484673 PMCID: PMC6829155 DOI: 10.1534/g3.119.400662] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Protein phosphatase V (PpV) encodes the Drosophila homolog of the evolutionarily conserved Protein Phosphatase 6 (PP6). The physiological and developmental functions of PpV/PP6 have not been well characterized due to lack of a genetically defined mutant. Here, we identified a PpV non-sense mutation and describe multiple mutant phenotypes in oogenesis and early embryogenesis. Specifically, we found that the defects in chromosome segregation during nuclear cycles are related to AuroraA function, which is consistent with the interaction of PP6 and AuroraA in mammalian cells. Surprisingly, we also identified a PpV function specifically in blastoderm cell cycle but not in cell proliferation in the follicle epithelium or larval wing imaginal discs. Embryos from PpV germline clones frequently undergo an extra nuclear division cycle. By epistasis analysis, we found that PpV functions in parallel with tribbles, but independently of auroraA for the remodeling of the nuclear cycles. Taken together, this study reports novel developmental functions of PpV and provides a framework for further genetic analysis under physiological conditions.
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19
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Liu B, Großhans J. The role of dNTP metabolites in control of the embryonic cell cycle. Cell Cycle 2019; 18:2817-2827. [PMID: 31544596 PMCID: PMC6791698 DOI: 10.1080/15384101.2019.1665948] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 09/03/2019] [Accepted: 09/06/2019] [Indexed: 01/06/2023] Open
Abstract
Deoxyribonucleotide metabolites (dNTPs) are the substrates for DNA synthesis. It has been proposed that their availability influences the progression of the cell cycle during development and pathological situations such as tumor growth. The mechanism has remained unclear for the link between cell cycle and dNTP levels beyond their role as substrates. Here, we review recent studies concerned with the dynamics of dNTP levels in early embryos and the role of DNA replication checkpoint as a sensor of dNTP levels.
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Affiliation(s)
- Boyang Liu
- Institut für Entwicklungsbiochemie, Universitätsmedizin, Georg-August-Universität, Göttingen, Germany
| | - Jörg Großhans
- Institut für Entwicklungsbiochemie, Universitätsmedizin, Georg-August-Universität, Göttingen, Germany
- Entwicklungsgenetik, Fachbereich Biologie, Philipps-Universität, Marburg, Germany
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20
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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: 38] [Impact Index Per Article: 6.3] [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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21
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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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22
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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: 266] [Impact Index Per Article: 44.3] [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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23
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Liu B, Winkler F, Herde M, Witte CP, Großhans J. A Link between Deoxyribonucleotide Metabolites and Embryonic Cell-Cycle Control. Curr Biol 2019; 29:1187-1192.e3. [PMID: 30880011 DOI: 10.1016/j.cub.2019.02.021] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 11/05/2018] [Accepted: 02/06/2019] [Indexed: 12/20/2022]
Abstract
The egg contains maternal RNAs and proteins, which have instrumental functions in patterning and morphogenesis. Besides these, the egg also contains metabolites, whose developmental functions have been little investigated. For example, the rapid increase of DNA content during the fast embryonic cell cycles poses high demands on the supply of deoxyribonucleotides (dNTPs), which may be synthesized in the embryo or maternally provided [1, 2]. Here, we analyze the role of dNTP in early Drosophila embryos. We found that dNTP levels initially decreased about 2-fold before reaching stable levels at the transition from syncytial to cellular blastoderm. Employing a mutant of the metabolic enzyme serine hydroxymethyl transferase (SHMT), which is impaired in the embryonic synthesis of deoxythymidine triphosphate (dTTP), we found that the maternal supply of dTTP was specifically depleted by interphase 13. SHMT mutants showed persistent S phase, replication stress, and a checkpoint-dependent cell-cycle arrest in NC13, depending on the loss of dTTP. The cell-cycle arrest in SHMT mutants was suppressed by reduced zygotic transcription. Consistent with the requirement of dTTP for cell-cycle progression, increased dNTP levels accelerated the cell cycle in embryos lacking zygotic transcription. We propose a model that both a limiting dNTP supply and interference of zygotic transcription with DNA replication [3] elicit DNA replication stress and checkpoint activation. Our study reveals a specific mechanism of how dNTP metabolites contribute to the embryonic cell-cycle control.
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Affiliation(s)
- Boyang Liu
- Institute for Developmental Biochemistry, Medical School, Georg August University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
| | - Franziska Winkler
- Institute for Developmental Biochemistry, Medical School, Georg August University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
| | - Marco Herde
- Institute of Plant Nutrition, Leibniz University Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany
| | - Claus-Peter Witte
- Institute of Plant Nutrition, Leibniz University Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany
| | - Jörg Großhans
- Institute for Developmental Biochemistry, Medical School, Georg August University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
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24
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Metabolic Regulation of Developmental Cell Cycles and Zygotic Transcription. Curr Biol 2019; 29:1193-1198.e5. [PMID: 30880009 DOI: 10.1016/j.cub.2019.02.028] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Revised: 01/15/2019] [Accepted: 02/08/2019] [Indexed: 12/29/2022]
Abstract
The thirteen nuclear cleavages that give rise to the Drosophila blastoderm are some of the fastest known cell cycles [1]. Surprisingly, the fertilized egg is provided with at most one-third of the dNTPs needed to complete the thirteen rounds of DNA replication [2]. The rest must be synthesized by the embryo, concurrent with cleavage divisions. What is the reason for the limited supply of DNA building blocks? We propose that frugal control of dNTP synthesis contributes to the well-characterized deceleration of the cleavage cycles and is needed for robust accumulation of zygotic gene products. In support of this model, we demonstrate that when the levels of dNTPs are abnormally high, nuclear cleavages fail to sufficiently decelerate, the levels of zygotic transcription are dramatically reduced, and the embryo catastrophically fails early in gastrulation. Our work reveals a direct connection between metabolism, the cell cycle, and zygotic transcription.
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25
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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: 55] [Impact Index Per Article: 7.9] [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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26
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LOTUS domain protein MARF1 binds CCR4-NOT deadenylase complex to post-transcriptionally regulate gene expression in oocytes. Nat Commun 2018; 9:4031. [PMID: 30279526 PMCID: PMC6168497 DOI: 10.1038/s41467-018-06404-w] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 09/01/2018] [Indexed: 12/30/2022] Open
Abstract
Post-transcriptional regulation of gene expression plays an essential role during oocyte maturation. Here we report that Drosophila MARF1 (Meiosis Regulator And mRNA Stability Factor 1), which consists of one RNA-recognition motif and six tandem LOTUS domains with unknown molecular function, is essential for oocyte maturation. When tethered to a reporter mRNA, MARF1 post-transcriptionally silences reporter expression by shortening reporter mRNA poly-A tail length and thereby reducing reporter protein level. This activity is mediated by the MARF1 LOTUS domain, which binds the CCR4-NOT deadenylase complex. MARF1 binds cyclin A mRNA and shortens its poly-A tail to reduce Cyclin A protein level during oocyte maturation. This study identifies MARF1 as a regulator in oocyte maturation and defines the conserved LOTUS domain as a post-transcriptional effector domain that recruits CCR4-NOT deadenylase complex to shorten target mRNA poly-A tails and suppress their translation. The RNA-binding protein MARF1 is required for post-transcriptional regulation of mRNAs during mouse oogenesis. Here, by analyzing a Drosophila MARF1 mutant, the authors show that MARF1 recruits CCR4-NOT deadenylase to shorten the poly-A tails of target mRNAs such as cyclin A and suppress their translation during Drosophila oogenesis.
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27
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Rust K, Tiwari MD, Mishra VK, Grawe F, Wodarz A. Myc and the Tip60 chromatin remodeling complex control neuroblast maintenance and polarity in Drosophila. EMBO J 2018; 37:embj.201798659. [PMID: 29997178 DOI: 10.15252/embj.201798659] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Revised: 05/28/2018] [Accepted: 05/29/2018] [Indexed: 02/04/2023] Open
Abstract
Stem cells establish cortical polarity and divide asymmetrically to simultaneously maintain themselves and generate differentiating offspring cells. Several chromatin modifiers have been identified as stemness factors in mammalian pluripotent stem cells, but whether these factors control stem cell polarity and asymmetric division has not been investigated so far. We addressed this question in Drosophila neural stem cells called neuroblasts. We identified the Tip60 chromatin remodeling complex and its interaction partner Myc as regulators of genes required for neuroblast maintenance. Knockdown of Tip60 complex members results in loss of cortical polarity, symmetric neuroblast division, and premature differentiation through nuclear entry of the transcription factor Prospero. We found that aPKC is the key target gene of Myc and the Tip60 complex subunit Domino in regulating neuroblast polarity. Our transcriptome analysis further showed that Domino regulates the expression of mitotic spindle genes previously identified as direct Myc targets. Our findings reveal an evolutionarily conserved functional link between Myc, the Tip60 complex, and the molecular network controlling cell polarity and asymmetric cell division.
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Affiliation(s)
- Katja Rust
- Molecular Cell Biology, Institute I for Anatomy, University of Cologne Medical School, Cologne, Germany .,Cluster of Excellence-Cellular Stress Response in Aging-Associated Diseases (CECAD), Cologne, Germany.,Stem Cell Biology, Institute for Anatomy and Cell Biology, Georg-August University Göttingen, Göttingen, Germany.,Department of Anatomy and OB-GYN/RS, University of California, San Francisco, San Francisco, CA, USA
| | - Manu D Tiwari
- Molecular Cell Biology, Institute I for Anatomy, University of Cologne Medical School, Cologne, Germany.,Cluster of Excellence-Cellular Stress Response in Aging-Associated Diseases (CECAD), Cologne, Germany.,Stem Cell Biology, Institute for Anatomy and Cell Biology, Georg-August University Göttingen, Göttingen, Germany
| | - Vivek Kumar Mishra
- Department of Dermatology and the Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA, USA
| | - Ferdi Grawe
- Molecular Cell Biology, Institute I for Anatomy, University of Cologne Medical School, Cologne, Germany
| | - Andreas Wodarz
- Molecular Cell Biology, Institute I for Anatomy, University of Cologne Medical School, Cologne, Germany .,Cluster of Excellence-Cellular Stress Response in Aging-Associated Diseases (CECAD), Cologne, Germany.,Stem Cell Biology, Institute for Anatomy and Cell Biology, Georg-August University Göttingen, Göttingen, Germany
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28
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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: 52] [Impact Index Per Article: 7.4] [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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29
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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: 41] [Impact Index Per Article: 5.9] [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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30
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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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31
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Essential Function of the Serine Hydroxymethyl Transferase (SHMT) Gene During Rapid Syncytial Cell Cycles in Drosophila. G3-GENES GENOMES GENETICS 2017; 7:2305-2314. [PMID: 28515048 PMCID: PMC5499137 DOI: 10.1534/g3.117.043133] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Many metabolic enzymes are evolutionarily highly conserved and serve a central function in the catabolism and anabolism of cells. The serine hydroxymethyl transferase (SHMT) catalyzing the conversion of serine and glycine and vice versa feeds into tetrahydrofolate (THF)-mediated C1 metabolism. We identified a Drosophila mutation in SHMT (CG3011) in a screen for blastoderm mutants. Embryos from SHMT mutant germline clones specifically arrest the cell cycle in interphase 13 at the time of the midblastula transition (MBT) and prior to cellularization. The phenotype is due to a loss of enzymatic activity as it cannot be rescued by an allele with a point mutation in the catalytic center but by an allele based on the SHMT coding sequence from Escherichia coli. The onset of zygotic gene expression and degradation of maternal RNAs in SHMT mutant embryos are largely similar to that in wild-type embryos. The specific timing of the defects in SHMT mutants indicates that at least one of the SHMT-dependent metabolites becomes limiting in interphase 13, if it is not produced by the embryo. Our data suggest that mutant eggs contain maternally-provided and SHMT-dependent metabolites in amounts that suffice for early development until interphase 13.
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32
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Deneke VE, Melbinger A, Vergassola M, Di Talia S. Waves of Cdk1 Activity in S Phase Synchronize the Cell Cycle in Drosophila Embryos. Dev Cell 2017; 38:399-412. [PMID: 27554859 DOI: 10.1016/j.devcel.2016.07.023] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Revised: 06/13/2016] [Accepted: 07/26/2016] [Indexed: 01/16/2023]
Abstract
Embryos of most metazoans undergo rapid and synchronous cell cycles following fertilization. While diffusion is too slow for synchronization of mitosis across large spatial scales, waves of Cdk1 activity represent a possible process of synchronization. However, the mechanisms regulating Cdk1 waves during embryonic development remain poorly understood. Using biosensors of Cdk1 and Chk1 activities, we dissect the regulation of Cdk1 waves in the Drosophila syncytial blastoderm. We show that Cdk1 waves are not controlled by the mitotic switch but by a double-negative feedback between Cdk1 and Chk1. Using mathematical modeling and surgical ligations, we demonstrate a fundamental distinction between S phase Cdk1 waves, which propagate as active trigger waves in an excitable medium, and mitotic Cdk1 waves, which propagate as passive phase waves. Our findings show that in Drosophila embryos, Cdk1 positive feedback serves primarily to ensure the rapid onset of mitosis, while wave propagation is regulated by S phase events.
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Affiliation(s)
- Victoria E Deneke
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA
| | - Anna Melbinger
- Department of Physics, University of California San Diego, La Jolla, CA 92093, USA
| | - Massimo Vergassola
- Department of Physics, University of California San Diego, La Jolla, CA 92093, USA
| | - Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.
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33
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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: 1.0] [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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34
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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: 3.4] [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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35
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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: 4.8] [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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36
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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: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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37
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Human TRIB2 Oscillates during the Cell Cycle and Promotes Ubiquitination and Degradation of CDC25C. Int J Mol Sci 2016; 17:ijms17091378. [PMID: 27563873 PMCID: PMC5037658 DOI: 10.3390/ijms17091378] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Revised: 08/04/2016] [Accepted: 08/18/2016] [Indexed: 12/13/2022] Open
Abstract
Tribbles homolog 2 (TRIB2) is a member of the mammalian Tribbles family of serine/threonine pseudokinases (TRIB1-3). Studies of TRIB2 indicate that many of the molecular interactions between the single Drosophila Tribbles (Trbl) protein and interacting partners are evolutionary conserved. In this study, we examined the relationship between TRIB2 and cell division cycle 25 (CDC25) family of dual-specificity protein phosphatases (mammalian homologues of Drosophila String), which are key physiological cell cycle regulators. Using co-immunoprecipitation we demonstrate that TRIB2 interacts with CDC25B and CDC25C selectively. Forced overexpression of TRIB2 caused a marked decrease in total CDC25C protein levels. Following inhibition of the proteasome, CDC25C was stabilized in the nuclear compartment. This implicates TRIB2 as a regulator of nuclear CDC25C turnover. In complementary ubiquitination assays, we show that TRIB2-mediated degradation of CDC25C is associated with lysine-48-linked CDC25C polyubiquitination driven by the TRIB2 kinase-like domain. A cell cycle associated role for TRIB2 is further supported by the cell cycle regulated expression of TRIB2 protein levels. Our findings reveal mitotic CDC25C as a new target of TRIB2 that is degraded via the ubiquitin proteasome system. Inappropriate CDC25C regulation could mechanistically underlie TRIB2 mediated regulation of cellular proliferation in neoplastic cells.
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38
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Deneke VE, Melbinger A, Vergassola M, Di Talia S. Waves of Cdk1 Activity in S Phase Synchronize the Cell Cycle in Drosophila Embryos. Dev Cell 2016. [PMID: 27554859 DOI: 10.1016/j.devcel.2016.07.0240] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/21/2023]
Abstract
Embryos of most metazoans undergo rapid and synchronous cell cycles following fertilization. While diffusion is too slow for synchronization of mitosis across large spatial scales, waves of Cdk1 activity represent a possible process of synchronization. However, the mechanisms regulating Cdk1 waves during embryonic development remain poorly understood. Using biosensors of Cdk1 and Chk1 activities, we dissect the regulation of Cdk1 waves in the Drosophila syncytial blastoderm. We show that Cdk1 waves are not controlled by the mitotic switch but by a double-negative feedback between Cdk1 and Chk1. Using mathematical modeling and surgical ligations, we demonstrate a fundamental distinction between S phase Cdk1 waves, which propagate as active trigger waves in an excitable medium, and mitotic Cdk1 waves, which propagate as passive phase waves. Our findings show that in Drosophila embryos, Cdk1 positive feedback serves primarily to ensure the rapid onset of mitosis, while wave propagation is regulated by S phase events.
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Affiliation(s)
- Victoria E Deneke
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA
| | - Anna Melbinger
- Department of Physics, University of California San Diego, La Jolla, CA 92093, USA
| | - Massimo Vergassola
- Department of Physics, University of California San Diego, La Jolla, CA 92093, USA
| | - Stefano Di Talia
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.
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39
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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: 3.0] [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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40
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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: 59] [Impact Index Per Article: 6.6] [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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41
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Mondal D, Mathur A, Chandra PK. Tripping on TRIB3 at the junction of health, metabolic dysfunction and cancer. Biochimie 2016; 124:34-52. [DOI: 10.1016/j.biochi.2016.02.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Accepted: 02/04/2016] [Indexed: 12/16/2022]
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42
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Elgart M, Stern S, Salton O, Gnainsky Y, Heifetz Y, Soen Y. Impact of gut microbiota on the fly's germ line. Nat Commun 2016; 7:11280. [PMID: 27080728 PMCID: PMC4835552 DOI: 10.1038/ncomms11280] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 03/09/2016] [Indexed: 12/20/2022] Open
Abstract
Unlike vertically transmitted endosymbionts, which have broad effects on their host's germ line, the extracellular gut microbiota is transmitted horizontally and is not known to influence the germ line. Here we provide evidence supporting the influence of these gut bacteria on the germ line of Drosophila melanogaster. Removal of the gut bacteria represses oogenesis, expedites maternal-to-zygotic-transition in the offspring and unmasks hidden phenotypic variation in mutants. We further show that the main impact on oogenesis is linked to the lack of gut Acetobacter species, and we identify the Drosophila Aldehyde dehydrogenase (Aldh) gene as an apparent mediator of repressed oogenesis in Acetobacter-depleted flies. The finding of interactions between the gut microbiota and the germ line has implications for reproduction, developmental robustness and adaptation. The gut microbiota can play various roles in the host's physiology, but is not known to influence the germ line. Here, Elgart et al. show that certain extracellular gut bacteria can affect oogenesis and embryo development in the fruit fly.
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Affiliation(s)
- Michael Elgart
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Shay Stern
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Orit Salton
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yulia Gnainsky
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yael Heifetz
- Department of Entomology, The Hebrew University, Rehovot 76100, Israel
| | - Yoav Soen
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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43
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Park H, Yoo S. vnd and its target gene twine are required for cell cycle progression during embryonic nervous system development in Drosophila melanogaster. Genes Genomics 2016. [DOI: 10.1007/s13258-015-0371-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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44
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Zhang M, Kothari P, Mullins M, Lampson MA. Regulation of zygotic genome activation and DNA damage checkpoint acquisition at the mid-blastula transition. Cell Cycle 2015; 13:3828-38. [PMID: 25558827 DOI: 10.4161/15384101.2014.967066] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Following fertilization, oviparous embryos undergo rapid, mostly transcriptionally silent cleavage divisions until the mid-blastula transition (MBT), when large-scale developmental changes occur, including zygotic genome activation (ZGA) and cell cycle remodeling, via lengthening and checkpoint acquisition. Despite their concomitant appearance, whether these changes are co-regulated is unclear. Three models have been proposed to account for the timing of (ZGA). One model implicates a threshold nuclear to cytoplasmic (N:C) ratio, another stresses the importance cell cycle elongation, while the third model invokes a timer mechanism. We show that precocious Chk1 activity in pre-MBT zebrafish embryos elongates cleavage cycles, thereby slowing the increase in the N:C ratio. We find that cell cycle elongation does not lead to transcriptional activation. Rather, ZGA slows in parallel with the N:C ratio. We show further that the DNA damage checkpoint program is maternally supplied and independent of ZGA. Although pre-MBT embryos detect damage and activate Chk2 after induction of DNA double-strand breaks, the Chk1 arm of the DNA damage response is not activated, and the checkpoint is nonfunctional. Our results are consistent with the N:C ratio model for ZGA. Moreover, the ability of precocious Chk1 activity to delay pre-MBT cell cycles indicate that lack of Chk1 activity limits checkpoint function during cleavage cycles. We propose that Chk1 gain-of-function at the MBT underlies cell cycle remodeling, whereas ZGA is regulated independently by the N:C ratio.
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45
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O'Farrell PH. Growing an Embryo from a Single Cell: A Hurdle in Animal Life. Cold Spring Harb Perspect Biol 2015; 7:cshperspect.a019042. [PMID: 26254311 DOI: 10.1101/cshperspect.a019042] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A requirement that an animal be able to feed to grow constrains how a cell can grow into an animal, and it forces an alternation between growth (increase in mass) and proliferation (increase in cell number). A growth-only phase that transforms a stem cell of ordinary proportions into a huge cell, the oocyte, requires dramatic adaptations to help a nucleus direct a 10(5)-fold expansion of cytoplasmic volume. Proliferation without growth transforms the huge egg into an embryo while still accommodating an impotent nucleus overwhelmed by the voluminous cytoplasm. This growth program characterizes animals that deposit their eggs externally, but it is changed in mammals and in endoparasites. In these organisms, development in a nutritive environment releases the growth constraint, but growth of cells before gastrulation requires a new program to sustain pluripotency during this growth.
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Affiliation(s)
- Patrick H O'Farrell
- Department of Biochemistry, University of California San Francisco, San Francisco, California 94158
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46
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Hatzihristidis T, Desai N, Hutchins AP, Meng TC, Tremblay ML, Miranda-Saavedra D. A Drosophila-centric view of protein tyrosine phosphatases. FEBS Lett 2015; 589:951-66. [PMID: 25771859 DOI: 10.1016/j.febslet.2015.03.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 03/02/2015] [Accepted: 03/02/2015] [Indexed: 12/30/2022]
Abstract
Most of our knowledge on protein tyrosine phosphatases (PTPs) is derived from human pathologies and mouse knockout models. These models largely correlate well with human disease phenotypes, but can be ambiguous due to compensatory mechanisms introduced by paralogous genes. Here we present the analysis of the PTP complement of the fruit fly and the complementary view that PTP studies in Drosophila will accelerate our understanding of PTPs in physiological and pathological conditions. With only 44 PTP genes, Drosophila represents a streamlined version of the human complement. Our integrated analysis places the Drosophila PTPs into evolutionary and functional contexts, thereby providing a platform for the exploitation of the fly for PTP research and the transfer of knowledge onto other model systems.
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Affiliation(s)
- Teri Hatzihristidis
- Goodman Cancer Research Centre, McGill University, 1160 Pine Avenue, Montreal, Québec H3A 1A3, Canada; Department of Medicine, Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada
| | - Nikita Desai
- Goodman Cancer Research Centre, McGill University, 1160 Pine Avenue, Montreal, Québec H3A 1A3, Canada; Department of Biochemistry, McGill University, Montreal, Quebec, Canada
| | - Andrew P Hutchins
- Key Laboratory of Regenerative Biology and Guangdong Provincial Key Laboratory of Stem Cell and Regenerative Medicine, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, Guangdong 510530, China
| | - Tzu-Ching Meng
- Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan; Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan; Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
| | - Michel L Tremblay
- Goodman Cancer Research Centre, McGill University, 1160 Pine Avenue, Montreal, Québec H3A 1A3, Canada; Department of Medicine, Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada; Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
| | - Diego Miranda-Saavedra
- World Premier International (WPI) Immunology Frontier Research Center (IFReC), Osaka University, 3-1 Yamadaoka, Suita 565-0871, Osaka, Japan; Centro de Biología Molecular Severo Ochoa, CSIC/Universidad Autónoma de Madrid, 28049 Madrid, Spain; IE Business School, IE University, María de Molina 31 bis, 28006 Madrid, Spain.
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Amodeo AA, Jukam D, Straight AF, Skotheim JM. Histone titration against the genome sets the DNA-to-cytoplasm threshold for the Xenopus midblastula transition. Proc Natl Acad Sci U S A 2015; 112:E1086-95. [PMID: 25713373 PMCID: PMC4364222 DOI: 10.1073/pnas.1413990112] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
During early development, animal embryos depend on maternally deposited RNA until zygotic genes become transcriptionally active. Before this maternal-to-zygotic transition, many species execute rapid and synchronous cell divisions without growth phases or cell cycle checkpoints. The coordinated onset of transcription, cell cycle lengthening, and cell cycle checkpoints comprise the midblastula transition (MBT). A long-standing model in the frog, Xenopus laevis, posits that MBT timing is controlled by a maternally loaded inhibitory factor that is titrated against the exponentially increasing amount of DNA. To identify MBT regulators, we developed an assay using Xenopus egg extract that recapitulates the activation of transcription only above the DNA-to-cytoplasm ratio found in embryos at the MBT. We used this system to biochemically purify factors responsible for inhibiting transcription below the threshold DNA-to-cytoplasm ratio. This unbiased approach identified histones H3 and H4 as concentration-dependent inhibitory factors. Addition or depletion of H3/H4 from the extract quantitatively shifted the amount of DNA required for transcriptional activation in vitro. Moreover, reduction of H3 protein in embryos induced premature transcriptional activation and cell cycle lengthening, and the addition of H3/H4 shortened post-MBT cell cycles. Our observations support a model for MBT regulation by DNA-based titration and suggest that depletion of free histones regulates the MBT. More broadly, our work shows how a constant concentration DNA binding molecule can effectively measure the amount of cytoplasm per genome to coordinate division, growth, and development.
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Blythe SA, Wieschaus EF. Zygotic genome activation triggers the DNA replication checkpoint at the midblastula transition. Cell 2015; 160:1169-81. [PMID: 25748651 DOI: 10.1016/j.cell.2015.01.050] [Citation(s) in RCA: 131] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 11/03/2014] [Accepted: 01/08/2015] [Indexed: 11/16/2022]
Abstract
A conserved feature of the midblastula transition (MBT) is a requirement for a functional DNA replication checkpoint to coordinate cell-cycle remodeling and zygotic genome activation (ZGA). We have investigated what triggers this checkpoint during Drosophila embryogenesis. We find that the magnitude of the checkpoint scales with the quantity of transcriptionally engaged DNA. Measuring RNA polymerase II (Pol II) binding at 20 min intervals over the course of ZGA reveals that the checkpoint coincides with widespread de novo recruitment of Pol II that precedes and does not require a functional checkpoint. This recruitment drives slowing or stalling of DNA replication at transcriptionally engaged loci. Reducing Pol II recruitment in zelda mutants both reduces replication stalling and bypasses the requirement for a functional checkpoint. This suggests a model where the checkpoint functions as a feedback mechanism to remodel the cell cycle in response to nascent ZGA.
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Affiliation(s)
- Shelby A Blythe
- Department of Molecular Biology, Howard Hughes Medical Institute, Princeton University, Princeton, NJ 08544, USA
| | - Eric F Wieschaus
- Department of Molecular Biology, Howard Hughes Medical Institute, Princeton University, Princeton, NJ 08544, USA.
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Coordinating Cell Cycle Remodeling with Transcriptional Activation at the Drosophila MBT. Curr Top Dev Biol 2015; 113:113-48. [DOI: 10.1016/bs.ctdb.2015.06.002] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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50
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Langley AR, Smith JC, Stemple DL, Harvey SA. New insights into the maternal to zygotic transition. Development 2014; 141:3834-41. [PMID: 25294937 DOI: 10.1242/dev.102368] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The initial phases of embryonic development occur in the absence of de novo transcription and are instead controlled by maternally inherited mRNAs and proteins. During this initial period, cell cycles are synchronous and lack gap phases. Following this period of transcriptional silence, zygotic transcription begins, the maternal influence on development starts to decrease, and dramatic changes to the cell cycle take place. Here, we discuss recent work that is shedding light on the maternal to zygotic transition and the interrelated but distinct mechanisms regulating the onset of zygotic transcription and changes to the cell cycle during early embryonic development.
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Affiliation(s)
- Alexander R Langley
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK
| | - James C Smith
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK
| | - Derek L Stemple
- The Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK
| | - Steven A Harvey
- The Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK
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