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Current Opinion in Genetics &... Oct 2020After fertilization, mouse embryos go through preimplantation development to give rise to blastocyst. Two key molecular events, zygotic genome activation (ZGA) and the... (Review)
Review
After fertilization, mouse embryos go through preimplantation development to give rise to blastocyst. Two key molecular events, zygotic genome activation (ZGA) and the first cell lineage specification, are essential for the process. Recent advances in low-input epigenomics profiling techniques allow the analysis of these events at a molecular level, which revealed a critical role of epigenetic and chromatin reprogramming in ZGA and the first cell lineage specification. Additionally, the establishment of an in vitro embryonic stem cell (ESC) to two-cell embryo-like conversion system have also contributed to the molecular understanding of preimplantation development. In this review, we summarize recent advances in epigenetic regulation of mouse preimplantation development, point out the remaining questions, and propose strategies to tackle these questions.
Topics: Animals; Blastocyst; Embryonic Development; Embryonic Stem Cells; Epigenesis, Genetic; Female; Genome; Humans; Pregnancy; Zygote
PubMed: 32563750
DOI: 10.1016/j.gde.2020.05.015 -
Current Topics in Developmental Biology 2021The fertilized frog egg contains all the materials needed to initiate development of a new organism, including stored RNAs and proteins deposited during oogenesis, thus... (Review)
Review
The fertilized frog egg contains all the materials needed to initiate development of a new organism, including stored RNAs and proteins deposited during oogenesis, thus the earliest stages of development do not require transcription. The onset of transcription from the zygotic genome marks the first genetic switch activating the gene regulatory network that programs embryonic development. Zygotic genome activation occurs after an initial phase of transcriptional quiescence that continues until the midblastula stage, a period called the midblastula transition, which was first identified in Xenopus. Activation of transcription is programmed by maternally supplied factors and is regulated at multiple levels. A similar switch exists in most animals and is of great interest both to developmental biologists and to those interested in understanding nuclear reprogramming. Here we review in detail our knowledge on this major switch in transcription in Xenopus and place recent discoveries in the context of a decades old problem.
Topics: Animals; Genome; Oogenesis; Xenopus laevis; Zygote
PubMed: 34074529
DOI: 10.1016/bs.ctdb.2021.03.003 -
FEBS Letters Sep 2018Since their discovery, the study of maternal mRNAs has led to the identification of mechanisms underlying their spatiotemporal regulation within the context of oogenesis... (Review)
Review
Since their discovery, the study of maternal mRNAs has led to the identification of mechanisms underlying their spatiotemporal regulation within the context of oogenesis and early embryogenesis. Following synthesis in the oocyte, maternal mRNAs are translationally silenced and sequestered into storage in cytoplasmic granules. At the same time, their unique distribution patterns throughout the oocyte and embryo are tightly controlled and connected to their functions in downstream embryonic processes. At certain points in oogenesis and early embryogenesis, maternal mRNAs are translationally activated to perform their functions in a timely manner. The cytoplasmic polyadenylation machinery is responsible for the translational activation of maternal mRNAs, and its role in initiating the maternal to zygotic transition events has recently come to light. Here, we summarize the current knowledge on maternal mRNA regulation, with particular focus on cytoplasmic polyadenylation as a mechanism for translational regulation.
Topics: Animals; Female; Gene Expression Regulation, Developmental; Humans; Oogenesis; Polyadenylation; RNA Interference; RNA Processing, Post-Transcriptional; RNA, Messenger; RNA, Messenger, Stored; Zygote
PubMed: 29972882
DOI: 10.1002/1873-3468.13183 -
The International Journal of... 2019Mammalian oocytes/zygotes contain atypical nucleoli that are composed exclusively of a dense fibrillar material. It has been commonly accepted that these nucleoli serve... (Review)
Review
Mammalian oocytes/zygotes contain atypical nucleoli that are composed exclusively of a dense fibrillar material. It has been commonly accepted that these nucleoli serve as a repository of components that are used later on, as the embryo develops, for the construction of typical tripartite nucleoli. Indeed, when nucleoli were removed from immature oocytes (enucleolation) and these oocytes were then matured, fertilized or parthenogenetically activated, development of the produced embryos ceased after one or two cleavages with no detectable nucleoli in nuclei. This indicated that zygotic nucleoli originate exclusively from oocytes, i.e. are maternally inherited. Recently published results, however, do not support this developmental biology dogma and demonstrate that maternal nucleoli in one-cell stage embryos are necessary only during a very short time period after fertilization when they serve as a major heterochromatin organizing structures. Nevertheless, it still remains to be determined, which other functions/roles the atypical oocyte/zygote nucleoli eventually have.
Topics: Animals; Cell Nucleolus; Embryo, Mammalian; Embryonic Development; Female; Fertilization; Heterochromatin; Humans; Maternal Inheritance; Mice; Nucleoplasmins; Oocytes; Time Factors; Zygote
PubMed: 31058290
DOI: 10.1387/ijdb.180329jf -
Cells Sep 2021Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex...
Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex is facultative in many relevant taxa (e.g., algae) that harbour both anisogamous and isogamous species. Here, we complement this recent analysis with an approach where we assume that the relationship between progeny size and its survival may differ between parthenogenetically and sexually produced progeny, favouring either the former or the latter. We show that previous findings that parthenogenesis can stabilise isogamy relative to the obligate sex case, extend to our scenarios. We additionally investigate two different ways for one mating type to take over the entire population. First, parthenogenesis can lead to biased sex ratios that are sufficiently extreme that one type can displace the other, leading to de facto asexuality for the remaining type that now lacks partners to fuse with. This process involves positive feedback: microgametes, being numerous, lack opportunities for syngamy, and should they proliferate parthenogenetically, the next generation makes this asexual route even more prominent for microgametes. Second, we consider mutations to strict asexuality in producers of micro- or macrogametes, and show that the prospects of asexual invasion depend strongly on the mating type in which the mutation arises. Perhaps most interestingly, we also find scenarios in which parthenogens have an intrinsic survival advantage yet facultatively sexual isogamous populations are robust to the invasion of asexuals, despite us assuming no genetic benefits of recombination. Here, equal contribution from both mating types to zygotes that are sufficiently well provisioned can outweigh the additional costs associated with syngamy.
Topics: Biological Evolution; Gametogenesis; Germ Cells; Models, Biological; Mutation; Parthenogenesis; Phaeophyceae; Zygote
PubMed: 34572116
DOI: 10.3390/cells10092467 -
Cell Reports Jun 2020After fertilization, sperm and oocyte nuclei are rapidly remodeled to form swollen pronuclei (PN) in mammalian zygotes, and the proper formation and function of PN are...
After fertilization, sperm and oocyte nuclei are rapidly remodeled to form swollen pronuclei (PN) in mammalian zygotes, and the proper formation and function of PN are key to producing totipotent zygotes. However, how mature PN are formed has been unclear. We find that filamentous actin (F-actin) assembles in the PN of mouse zygotes and is required for fully functional PN. The perturbation of nuclear actin dynamics in zygotes results in the misregulation of genes related to genome integrity and abnormal development of mouse embryos. We show that nuclear F-actin ensures DNA damage repair, thus preventing the activation of a zygotic checkpoint. Furthermore, optogenetic control of cofilin nuclear localization reveals the dynamically regulated F-actin nucleoskeleton in zygotes, and its timely disassembly is needed for developmental progression. Nuclear F-actin is a hallmark of totipotent zygotic PN, and the temporal regulation of its polymerized state is necessary for normal embryonic development.
Topics: Actin Cytoskeleton; Actin Depolymerizing Factors; Actins; Animals; Cell Cycle Checkpoints; Cell Nucleus; Cell Survival; Checkpoint Kinase 1; DNA Damage; Embryo, Mammalian; Embryonic Development; Gene Expression Regulation, Developmental; Imaging, Three-Dimensional; Light; Mice, Inbred ICR; Mitosis; Polymerization; Up-Regulation; Zygote
PubMed: 32610125
DOI: 10.1016/j.celrep.2020.107824 -
The New Phytologist Sep 2016Contents 1170 I. 1170 II. 1172 III. 1175 IV. 1180 V. 1183 1184 References 1184 SUMMARY: An unintended consequence of global change is an increase in opportunities for... (Review)
Review
Contents 1170 I. 1170 II. 1172 III. 1175 IV. 1180 V. 1183 1184 References 1184 SUMMARY: An unintended consequence of global change is an increase in opportunities for hybridization among previously isolated lineages. Here we illustrate how global change can facilitate the breakdown of reproductive barriers and the formation of hybrids, drawing on the flora of the British Isles for insight. Although global change may ameliorate some of the barriers preventing hybrid establishment, for example by providing new ecological niches for hybrids, it will have limited effects on environment-independent post-zygotic barriers. For example, genic incompatibilities and differences in chromosome numbers and structure within hybrid genomes are unlikely to be affected by global change. We thus speculate that global change will have a larger effect on eroding pre-zygotic barriers (eco-geographical isolation and phenology) than post-zygotic barriers, shifting the relative importance of these two classes of reproductive barriers from what is usually seen in naturally produced hybrids where pre-zygotic barriers are the largest contributors to reproductive isolation. Although the long-term fate of neo-hybrids is still to be determined, the massive impact of global change on the dynamics and distribution of biodiversity generates an unprecedented opportunity to study large numbers of unpredicted, and often replicated, hybridization 'experiments', allowing us to peer into the birth and death of evolutionary lineages.
Topics: Climate Change; Ecosystem; Genetic Speciation; Hybridization, Genetic; Plant Infertility; Zygote
PubMed: 27214560
DOI: 10.1111/nph.14004 -
Biochimica Et Biophysica Acta Jul 2015The zygote is the essential intermediate that allows interchange of nuclear, mitochondrial and cytosolic determinants between cells. Zygote formation in Saccharomyces... (Review)
Review
The zygote is the essential intermediate that allows interchange of nuclear, mitochondrial and cytosolic determinants between cells. Zygote formation in Saccharomyces cerevisiae is accomplished by mechanisms that are not characteristic of mitotic cells. These include shifting the axis of growth away from classical cortical landmarks, dramatically reorganizing the cell cortex, remodeling the cell wall in preparation for cell fusion, fusing with an adjacent partner, accomplishing nuclear fusion, orchestrating two steps of septin morphogenesis that account for a delay in fusion of mitochondria, and implementing new norms for bud site selection. This essay emphasizes the sequence of dependent relationships that account for this progression from cell encounters through zygote budding. It briefly summarizes classical studies of signal transduction and polarity specification and then focuses on downstream events.
Topics: Cell Wall; Models, Biological; Osmosis; Transcription, Genetic; Yeasts; Zygote
PubMed: 25862405
DOI: 10.1016/j.bbamcr.2015.03.018 -
Nature Cell Biology Apr 2020The importance of germline-inherited post-translational histone modifications on priming early mammalian development is just emerging. Histone H3 lysine 9 (H3K9)...
The importance of germline-inherited post-translational histone modifications on priming early mammalian development is just emerging. Histone H3 lysine 9 (H3K9) trimethylation is associated with heterochromatin and gene repression during cell-fate change, whereas histone H3 lysine 4 (H3K4) trimethylation marks active gene promoters. Mature oocytes are transcriptionally quiescent and possess remarkably broad domains of H3K4me3 (bdH3K4me3). It is unknown which factors contribute to the maintenance of the bdH3K4me3 landscape. Lysine-specific demethylase 4A (KDM4A) demethylates H3K9me3 at promoters marked by H3K4me3 in actively transcribing somatic cells. Here, we report that KDM4A-mediated H3K9me3 demethylation at bdH3K4me3 in oocytes is crucial for normal pre-implantation development and zygotic genome activation after fertilization. The loss of KDM4A in oocytes causes aberrant H3K9me3 spreading over bdH3K4me3, resulting in insufficient transcriptional activation of genes, endogenous retroviral elements and chimeric transcripts initiated from long terminal repeats during zygotic genome activation. The catalytic activity of KDM4A is essential for normal epigenetic reprogramming and pre-implantation development. Hence, KDM4A plays a crucial role in preserving the maternal epigenome integrity required for proper zygotic genome activation and transfer of developmental control to the embryo.
Topics: Animals; Embryo Implantation; Embryo, Mammalian; Female; Fertilization; Heterochromatin; Histone Demethylases; Histones; Male; Metaphase; Methylation; Mice; Mice, Knockout; Oocytes; Promoter Regions, Genetic; Protein Processing, Post-Translational; Transcription, Genetic; Zygote
PubMed: 32231309
DOI: 10.1038/s41556-020-0494-z -
The Journal of Reproduction and... Apr 2022The zygotic genome is transcriptionally silent immediately after fertilization. In mice, initial activation of the zygotic genome occurs in the middle of the one-cell... (Review)
Review
The zygotic genome is transcriptionally silent immediately after fertilization. In mice, initial activation of the zygotic genome occurs in the middle of the one-cell stage. At the mid-to-late two-cell stage, a burst of gene activation occurs after the second round of DNA replication, and the profile of transcribed genes changes dramatically. These two phases of gene activation are called minor and major zygotic gene activation (ZGA), respectively. As they mark the beginning of the gene expression program, it is important to elucidate gene expression regulation during these stages. This article reviews the outcomes of studies that have clarified the profiles and regulatory mechanisms of ZGA.
Topics: Animals; DNA Replication; Embryonic Development; Gene Expression Regulation, Developmental; Genome; Mice; Transcriptional Activation; Zygote
PubMed: 35034936
DOI: 10.1262/jrd.2021-129