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Plant Physiology Jan 2017A comparison of eudicot and monocot model plants explores recent advances and open questions on gene regulatory networks during zygote development, parental influences... (Review)
Review
A comparison of eudicot and monocot model plants explores recent advances and open questions on gene regulatory networks during zygote development, parental influences on early embryogenesis, zygotic genome activation, and cell fate determination.
Topics: Cell Communication; Cell Differentiation; Cell Division; Cell Lineage; Gene Regulatory Networks; Genome, Plant; Genomic Imprinting; Indoleacetic Acids; Magnoliopsida; Plant Growth Regulators; Zygote
PubMed: 27909044
DOI: 10.1104/pp.16.01406 -
The Journal of Reproduction and... Aug 2017After fertilization, the genomes derived from an oocyte and spermatozoon are in a transcriptionally silent state before becoming activated at a species-specific time. In... (Review)
Review
After fertilization, the genomes derived from an oocyte and spermatozoon are in a transcriptionally silent state before becoming activated at a species-specific time. In mice, the initiation of transcription occurs at the mid-one-cell stage, which represents the start of the gene expression program. A recent RNA sequencing analysis revealed that the gene expression pattern of one-cell embryos is unique and changes dramatically at the two-cell stage. However, the mechanism regulating this alteration has not yet been elucidated. It has been shown that chromatin structure and epigenetic factors change dynamically between the one- and two-cell stages. In this article, we review the characteristics of transcription, chromatin structure, and epigenetic factors in one- and two-cell mouse embryos and discuss the involvement of chromatin structure and epigenetic factors in the alteration of transcription that occurs between these stages.
Topics: Animals; Chromatin; Epigenesis, Genetic; Gene Expression Regulation, Developmental; Humans; Transcriptional Activation; Zygote
PubMed: 28579579
DOI: 10.1262/jrd.2017-058 -
Nature Communications Feb 2022Awakening of zygotic transcription in animal embryos relies on maternal pioneer transcription factors. The interplay of global and specific functions of these proteins...
Awakening of zygotic transcription in animal embryos relies on maternal pioneer transcription factors. The interplay of global and specific functions of these proteins remains poorly understood. Here, we analyze chromatin accessibility and time-resolved transcription in single and double mutant zebrafish embryos lacking pluripotency factors Pou5f3 and Sox19b. We show that two factors modify chromatin in a largely independent manner. We distinguish four types of direct enhancers by differential requirements for Pou5f3 or Sox19b. We demonstrate that changes in chromatin accessibility of enhancers underlie the changes in zygotic expression repertoire in the double mutants. Pou5f3 or Sox19b promote chromatin accessibility of enhancers linked to the genes involved in gastrulation and ventral fate specification. The genes regulating mesendodermal and dorsal fates are primed for activation independently of Pou5f3 and Sox19b. Strikingly, simultaneous loss of Pou5f3 and Sox19b leads to premature expression of genes, involved in regulation of organogenesis and differentiation.
Topics: Animals; Cell Differentiation; Chromatin; Female; Gastrulation; Gene Expression Regulation, Developmental; Genome; Male; Octamer Transcription Factor-3; SOX Transcription Factors; Transcription Factors; Zebrafish; Zebrafish Proteins; Zygote
PubMed: 35145080
DOI: 10.1038/s41467-022-28434-1 -
The Journal of Reproduction and... Jun 2024Totipotency refers to the ability of a single cell to give rise to all the different cell types in the body. Terminally differentiated germ cells (sperm and oocytes)... (Review)
Review
Totipotency refers to the ability of a single cell to give rise to all the different cell types in the body. Terminally differentiated germ cells (sperm and oocytes) undergo reprogramming, which results in the acquisition of totipotency in zygotes. Since the 1990s, numerous studies have focused on the mechanisms of totipotency. With the emergence of the concept of epigenetic reprogramming, which is important for the undifferentiated and differentiated states of cells, the epigenomes of germ cells and fertilized oocytes have been thoroughly analyzed. However, in early immunostaining studies, detailed epigenomic information was difficult to obtain. In recent years, the explosive development of next-generation sequencing has made it possible to acquire genome-wide information and the rise of genome editing has facilitated the analysis of knockout mice, which was previously difficult. In addition, live imaging can effectively analyze zygotes and 2-cell embryos, for which the number of samples is limited, and provides biological insights that cannot be obtained by other methods. In this review, the progress of our research using these advanced techniques is traced back from the present to its earliest years.
Topics: Animals; Mice; Chromatin; Blastocyst; Female; Embryonic Development; Epigenesis, Genetic; Zygote
PubMed: 38462486
DOI: 10.1262/jrd.2023-106 -
Open Biology Dec 2018The onset of metazoan development requires that two terminally differentiated germ cells, a sperm and an oocyte, become reprogrammed to the totipotent embryo, which can... (Review)
Review
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.
Topics: Animals; Drosophila melanogaster; Embryonic Development; Female; Gene Expression Regulation, Developmental; Male; RNA Stability; RNA, Messenger, Stored; Transcription, Genetic; Transcriptional Activation; Zygote
PubMed: 30977698
DOI: 10.1098/rsob.180183 -
Cellular and Molecular Life Sciences :... Feb 2017Notwithstanding the enormous reproductive potential encapsulated within a mature mammalian oocyte, these cells present only a limited window for fertilization before... (Review)
Review
Notwithstanding the enormous reproductive potential encapsulated within a mature mammalian oocyte, these cells present only a limited window for fertilization before defaulting to an apoptotic cascade known as post-ovulatory oocyte aging. The only cell with the capacity to rescue this potential is the fertilizing spermatozoon. Indeed, the union of these cells sets in train a remarkable series of events that endows the oocyte with the capacity to divide and differentiate into the trillions of cells that comprise a new individual. Traditional paradigms hold that, beyond the initial stimulation of fluctuating calcium (Ca) required for oocyte activation, the fertilizing spermatozoon plays limited additional roles in the early embryo. While this model has now been drawn into question in view of the recent discovery that spermatozoa deliver developmentally important classes of small noncoding RNAs and other epigenetic modulators to oocytes during fertilization, it is nevertheless apparent that the primary responsibility for oocyte activation rests with a modest store of maternally derived proteins and mRNA accumulated during oogenesis. It is, therefore, not surprising that widespread post-translational modifications, in particular phosphorylation, hold a central role in endowing these proteins with sufficient functional diversity to initiate embryonic development. Indeed, proteins targeted for such modifications have been linked to oocyte activation, recruitment of maternal mRNAs, DNA repair and resumption of the cell cycle. This review, therefore, seeks to explore the intimate relationship between Ca release and the suite of molecular modifications that sweep through the oocyte to ensure the successful union of the parental germlines and ensure embryogenic fidelity.
Topics: Animals; Calcium; Cations, Divalent; DNA Repair; Embryonic Development; Epigenesis, Genetic; Fertilization; Humans; Oocytes; Phosphorylation; Protein Processing, Post-Translational; Zygote
PubMed: 27604868
DOI: 10.1007/s00018-016-2356-1 -
Current Topics in Developmental Biology 2015In Xenopus, the germline is specified by the inheritance of germ-plasm components synthesized at the beginning of oogenesis. Only the cells in the early embryo that... (Review)
Review
In Xenopus, the germline is specified by the inheritance of germ-plasm components synthesized at the beginning of oogenesis. Only the cells in the early embryo that receive germ plasm, the primordial germ cells (PGCs), are competent to give rise to the gametes. Thus, germ-plasm components continue the totipotent potential exhibited by the oocyte into the developing embryo at a time when most cells are preprogrammed for somatic differentiation as dictated by localized maternal determinants. When zygotic transcription begins at the mid-blastula transition, the maternally set program for somatic differentiation is realized. At this time, genetic control is ceded to the zygotic genome, and developmental potential gradually becomes more restricted within the primary germ layers. PGCs are a notable exception to this paradigm and remain transcriptionally silent until the late gastrula. How the germ-cell lineage retains full potential while somatic cells become fate restricted is a tale of translational repression, selective degradation of somatic maternal determinants, and delayed activation of zygotic transcription.
Topics: Animals; Cell Lineage; Cytoskeleton; Female; Germ Cells; RNA Stability; Xenopus; Zygote
PubMed: 26358876
DOI: 10.1016/bs.ctdb.2015.07.021 -
Journal of Assisted Reproduction and... Nov 2021Assisted reproduction is presumed to increase monozygotic twin rates, with the possible contribution of laboratory and medical interventions. Monozygotic dichorionic... (Review)
Review
Assisted reproduction is presumed to increase monozygotic twin rates, with the possible contribution of laboratory and medical interventions. Monozygotic dichorionic gestations are supposed to originate from the splitting of an embryo during the first four days of development, before blastocyst formation. Single embryo transfers could result in dichorionic pregnancies, currently explained by embryo splitting as described in the worldwide used medical textbooks, or concomitant conception. However, such splitting has never been observed in human in vitro fertilization, and downregulated frozen cycles could also produce multiple gestations. Several models of the possible origins of dichorionicity have been suggested. However, some possible underlying mechanisms observed from assisted reproduction seem to have been overlooked. In this review, we aimed to document the current knowledge, criticize the accepted dogma, and propose new insights into the origin of zygosity and chorionicity.
Topics: Chorion; Female; Fertilization in Vitro; Humans; Pregnancy; Twinning, Dizygotic; Twinning, Monozygotic; Zygote
PubMed: 34398401
DOI: 10.1007/s10815-021-02294-y -
Genes & Development Feb 2023Zygotic genome activation has been extensively studied in a variety of systems including flies, frogs, and mammals. However, there is comparatively little known about...
Zygotic genome activation has been extensively studied in a variety of systems including flies, frogs, and mammals. However, there is comparatively little known about the precise timing of gene induction during the earliest phases of embryogenesis. Here we used high-resolution in situ detection methods, along with genetic and experimental manipulations, to study the timing of zygotic activation in the simple model chordate with minute-scale temporal precision. We found that two homologs in are the earliest genes that respond to FGF signaling. We present evidence for a FGF timing mechanism that is driven by ERK-mediated derepression of the ERF repressor. Depletion of ERF results in ectopic activation of FGF target genes throughout the embryo. A highlight of this timer is the sharp transition in FGF responsiveness between the eight- and 16-cell stages of development. We propose that this timer is an innovation of chordates that is also used by vertebrates.
Topics: Animals; Embryo, Nonmammalian; Zygote; Genome; Embryonic Development; Vertebrates; Gene Expression Regulation, Developmental; Mammals
PubMed: 36801820
DOI: 10.1101/gad.350164.122 -
Proceedings of the National Academy of... Feb 2019In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical-basal axis of the mature plant. The zygote is...
In most flowering plants, the asymmetric cell division of the zygote is the initial step in establishing the apical-basal axis of the mature plant. The zygote is polarized, possessing the nucleus at the apical tip and large vacuoles at the basal end. Despite their known polar localization, whether the positioning of the vacuoles and the nucleus is coordinated and what the role of the vacuole is in the asymmetric zygotic division remain elusive. In the present study, we utilized a live-cell imaging system to visualize the dynamics of vacuoles during the entire process of zygote polarization in Image analysis revealed that the vacuoles formed tubular strands around the apically migrating nucleus. They gradually accumulated at the basal region and filled the space, resulting in asymmetric distribution in the mature zygote. To assess the role of vacuoles in the zygote, we screened various vacuole mutants and identified that (), in which the vacuolar structural change was impaired, failed to form tubular vacuoles and to polarly distribute the vacuole. In , large vacuoles occupied the apical tip and thus nuclear migration was blocked, resulting in a more symmetric zygotic division. We further observed that tubular vacuole formation and asymmetric vacuolar distribution both depended on the longitudinal array of actin filaments. Overall, our results show that vacuolar dynamics is crucial not only for the polar distribution along actin filaments but also for adequate nuclear positioning, and consequently zygote-division asymmetry.
Topics: Actin Cytoskeleton; Arabidopsis; Arabidopsis Proteins; Asymmetric Cell Division; Cell Nucleus; Cell Polarity; Chloroplast Proteins; Fluorescent Antibody Technique; Mutation; Vacuoles; Zygote
PubMed: 30651313
DOI: 10.1073/pnas.1814160116