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Nature Nov 2020Zygotic genome activation (ZGA) is the first transcription event in life. However, it is unclear how RNA polymerase is engaged in initiating ZGA in mammals. Here, by...
Zygotic genome activation (ZGA) is the first transcription event in life. However, it is unclear how RNA polymerase is engaged in initiating ZGA in mammals. Here, by developing small-scale Tn5-assisted chromatin cleavage with sequencing (Stacc-seq), we investigated the landscapes of RNA polymerase II (Pol II) binding in mouse embryos. We found that Pol II undergoes 'loading', 'pre-configuration', and 'production' during the transition from minor ZGA to major ZGA. After fertilization, Pol II is preferentially loaded to CG-rich promoters and accessible distal regions in one-cell embryos (loading), in part shaped by the inherited parental epigenome. Pol II then initiates relocation to future gene targets before genome activation (pre-configuration), where it later engages in full transcription elongation upon major ZGA (production). Pol II also maintains low poising at inactive promoters after major ZGA until the blastocyst stage, coinciding with the loss of promoter epigenetic silencing factors. Notably, inhibition of minor ZGA impairs the Pol II pre-configuration and embryonic development, accompanied by aberrant retention of Pol II and ectopic expression of one-cell targets upon major ZGA. Hence, stepwise transition of Pol II occurs when mammalian life begins, and minor ZGA has a key role in the pre-configuration of transcription machinery and chromatin for genome activation.
Topics: Alleles; Animals; Chromatin; Embryo, Mammalian; Epigenome; Female; Gene Expression Regulation, Developmental; Genome; Male; Maternal Inheritance; Mice; Mice, Inbred C57BL; Oocytes; Promoter Regions, Genetic; RNA Polymerase II; Zygote
PubMed: 33116310
DOI: 10.1038/s41586-020-2847-y -
Nature Jan 2024DNA replication enables genetic inheritance across the kingdoms of life. Replication occurs with a defined temporal order known as the replication timing (RT) programme,...
DNA replication enables genetic inheritance across the kingdoms of life. Replication occurs with a defined temporal order known as the replication timing (RT) programme, leading to organization of the genome into early- or late-replicating regions. RT is cell-type specific, is tightly linked to the three-dimensional nuclear organization of the genome and is considered an epigenetic fingerprint. In spite of its importance in maintaining the epigenome, the developmental regulation of RT in mammals in vivo has not been explored. Here, using single-cell Repli-seq, we generated genome-wide RT maps of mouse embryos from the zygote to the blastocyst stage. Our data show that RT is initially not well defined but becomes defined progressively from the 4-cell stage, coinciding with strengthening of the A and B compartments. We show that transcription contributes to the precision of the RT programme and that the difference in RT between the A and B compartments depends on RNA polymerase II at zygotic genome activation. Our data indicate that the establishment of nuclear organization precedes the acquisition of defined RT features and primes the partitioning of the genome into early- and late-replicating domains. Our work sheds light on the establishment of the epigenome at the beginning of mammalian development and reveals the organizing principles of genome organization.
Topics: Animals; Mice; Blastocyst; Chromatin; DNA Replication Timing; Epigenome; Genome; RNA Polymerase II; Zygote; Embryo, Mammalian
PubMed: 38123678
DOI: 10.1038/s41586-023-06872-1 -
Seminars in Cell & Developmental Biology Jan 2023Brown algae are a group of multicellular, heterokont algae that have convergently evolved developmental complexity that rivals that of embryophytes, animals or fungi.... (Review)
Review
Brown algae are a group of multicellular, heterokont algae that have convergently evolved developmental complexity that rivals that of embryophytes, animals or fungi. Early in development, brown algal zygotes establish a basal and an apical pole, which will become respectively the basal system (holdfast) and the apical system (thallus) of the adult alga. Brown algae are interesting models for understanding the establishment of cell polarity in a broad evolutionary context, because they exhibit a large diversity of life cycles, reproductive strategies and, importantly, their zygotes are produced in large quantities free of parental tissue, with symmetry breaking and asymmetric division taking place in a highly synchronous manner. This review describes the current knowledge about the establishment of the apical-basal axis in the model brown seaweeds Ectocarpus, Dictyota, Fucus and Saccharina, highlighting the advantages and specific interests of each system. Ectocarpus is a genetic model system that allows access to the molecular basis of early development and life-cycle control over apical-basal polarity. The oogamous brown alga Fucus, together with emerging comparative models Dictyota and Saccharina, emphasize the diversity of strategies of symmetry breaking in determining a cell polarity vector in brown algae. A comparison with symmetry-breaking mechanisms in land plants, animals and fungi, reveals that the one-step zygote polarisation of Fucus compares well to Saccharomyces budding and Arabidopsis stomata development, while the two-phased symmetry breaking in the Dictyota zygote compares to Schizosaccharomyces fission, the Caenorhabditis anterior-posterior zygote polarisation and Arabidopsis prolate pollen polarisation. The apical-basal patterning in Saccharina zygotes on the other hand, may be seen as analogous to that of land plants. Overall, brown algae have the potential to bring exciting new information on how a single cell gives rise to an entire complex body plan.
Topics: Animals; Zygote; Arabidopsis; Phaeophyceae; Cell Polarity; Cell Division; Plants
PubMed: 35317961
DOI: 10.1016/j.semcdb.2022.03.008 -
Current Topics in Developmental Biology 2020Soon after fertilization the zebrafish embryo generates the pool of cells that will give rise to the germline and the three somatic germ layers of the embryo (ectoderm,... (Review)
Review
Soon after fertilization the zebrafish embryo generates the pool of cells that will give rise to the germline and the three somatic germ layers of the embryo (ectoderm, mesoderm and endoderm). As the basic body plan of the vertebrate embryo emerges, evolutionarily conserved developmental signaling pathways, including Bmp, Nodal, Wnt, and Fgf, direct the nearly totipotent cells of the early embryo to adopt gene expression profiles and patterns of cell behavior specific to their eventual fates. Several decades of molecular genetics research in zebrafish has yielded significant insight into the maternal and zygotic contributions and mechanisms that pattern this vertebrate embryo. This new understanding is the product of advances in genetic manipulations and imaging technologies that have allowed the field to probe the cellular, molecular and biophysical aspects underlying early patterning. The current state of the field indicates that patterning is governed by the integration of key signaling pathways and physical interactions between cells, rather than a patterning system in which distinct pathways are deployed to specify a particular cell fate. This chapter focuses on recent advances in our understanding of the genetic and molecular control of the events that impart cell identity and initiate the patterning of tissues that are prerequisites for or concurrent with movements of gastrulation.
Topics: Animals; Body Patterning; Embryo, Nonmammalian; Gastrula; Gastrulation; Gene Expression Regulation, Developmental; Signal Transduction; Zebrafish; Zebrafish Proteins; Zygote
PubMed: 31959294
DOI: 10.1016/bs.ctdb.2019.08.002 -
Cells Feb 2020The zygote is defined as a diploid cell resulting from the fusion of two haploid gametes. Union of haploid male and female pronuclei in many animals occurs through... (Review)
Review
The zygote is defined as a diploid cell resulting from the fusion of two haploid gametes. Union of haploid male and female pronuclei in many animals occurs through rearrangements of the microtubule cytoskeleton into a radial array of microtubules known as the sperm aster. The sperm aster nucleates from paternally-derived centrioles attached to the male pronucleus after fertilization. Nematode, echinoderm, and amphibian eggs have proven as invaluable models to investigate the biophysical principles for how the sperm aster unites male and female pronuclei with precise spatial and temporal regulation. In this review, we compare these model organisms, discussing the dynamics of sperm aster formation and the different force generating mechanism for sperm aster and pronuclear migration. Finally, we provide new mechanistic insights for how sperm aster growth may influence sperm aster positioning.
Topics: Animals; Cell Nucleus; Female; Fertilization; Humans; Male; Microtubule-Organizing Center; Microtubules; Oocytes; Spermatozoa; Zygote
PubMed: 32102180
DOI: 10.3390/cells9020505 -
Current Biology : CB Jun 2024Rapid cleavage divisions and the transition from maternal to zygotic control of gene expression are the hallmarks of early embryonic development in most species. Early... (Review)
Review
Rapid cleavage divisions and the transition from maternal to zygotic control of gene expression are the hallmarks of early embryonic development in most species. Early development in insects, fish and amphibians is characterized by several short cell cycles with no gap phases, necessary for the rapid production of cells prior to patterning and morphogenesis. Maternal mRNAs and proteins loaded into the egg during oogenesis are essential to drive these rapid early divisions. Once the function of these maternal inputs is complete, the maternal-to-zygotic transition (MZT) marks the handover of developmental control to the gene products synthesized from the zygotic genome. The MZT requires three major events: the removal of a subset of maternal mRNAs, the initiation of zygotic transcription, and the remodeling of the cell cycle. In each species, the MZT occurs at a highly reproducible time during development due to a series of feedback mechanisms that tightly couple these three processes. Dissecting these feedback mechanisms and their spatiotemporal control will be essential to understanding the control of the MZT. In this primer, we outline the mechanisms that govern the major events of the MZT across species and highlight the role of feedback mechanisms that ensure the MZT is precisely timed and orchestrated.
Topics: Zygote; Animals; Gene Expression Regulation, Developmental; Embryonic Development; Female; RNA, Messenger, Stored
PubMed: 38834020
DOI: 10.1016/j.cub.2024.04.044 -
Annual Review of Cell and Developmental... Oct 2020Understanding human embryology has historically relied on comparative approaches using mammalian model organisms. With the advent of low-input methods to investigate... (Comparative Study)
Comparative Study Review
Understanding human embryology has historically relied on comparative approaches using mammalian model organisms. With the advent of low-input methods to investigate genetic and epigenetic mechanisms and efficient techniques to assess gene function, we can now study the human embryo directly. These advances have transformed the investigation of early embryogenesis in nonrodent species, thereby providing a broader understanding of conserved and divergent mechanisms. Here, we present an overview of the major events in human preimplantation development and place them in the context of mammalian evolution by comparing these events in other eutherian and metatherian species. We describe the advances of studies on postimplantation development and discuss stem cell models that mimic postimplantation embryos. A comparative perspective highlights the importance of analyzing different organisms with molecular characterization and functional studies to reveal the principles of early development. This growing field has a fundamental impact in regenerative medicine and raises important ethical considerations.
Topics: Animals; Embryonic Development; Embryonic Stem Cells; Humans; Models, Biological; Phylogeny; Zygote
PubMed: 33021826
DOI: 10.1146/annurev-cellbio-022020-024900 -
Methods in Molecular Biology (Clifton,... 2022Creating mouse models of human genetic disease (Gurumurthy and Lloyd, Dis Models Mech 12(1):dmm029462, 2019) and livestock trait (Schering et al. Arch Physiol Biochem...
Creating mouse models of human genetic disease (Gurumurthy and Lloyd, Dis Models Mech 12(1):dmm029462, 2019) and livestock trait (Schering et al. Arch Physiol Biochem 121(5):194-205, 2015; Habiela et al. J Gen Virol 95 (Pt 11):2329-2345, 2014) have been proven to be a useful tool for understanding the mechanism behind the phenotypes and fundamental and applied research in livestock. A single base pair deletion of prolactin receptor (PRLR) has an impact on hair morphology phenotypes beyond its classical roles in lactation in cattle, the so-called slick cattle (Littlejohn et al. Nat Commun 5:5861, 2014). Here, we generate a knock-in mouse model by targeting the specific locus of PRLR gene using Cas9-mediated genome editing via homology-directed repair (HDR) in mouse zygotes. The mouse model carrying the identical PRLR mutation in slick cattle may provide a useful animal model to study the pathway of thermoregulation and the mechanism of heat-tolerance in the livestock.
Topics: Animals; CRISPR-Cas Systems; Cattle; Female; Gene Editing; Hot Temperature; Mice; Recombinational DNA Repair; Zygote
PubMed: 35696038
DOI: 10.1007/978-1-0716-2301-5_14 -
Annual Review of Biochemistry Jun 2020The zona pellucida (ZP) is an extracellular matrix that surrounds all mammalian oocytes, eggs, and early embryos and plays vital roles during oogenesis, fertilization,... (Review)
Review
The zona pellucida (ZP) is an extracellular matrix that surrounds all mammalian oocytes, eggs, and early embryos and plays vital roles during oogenesis, fertilization, and preimplantation development. The ZP is composed of three or four glycosylated proteins, ZP1-4, that are synthesized, processed, secreted, and assembled into long, cross-linked fibrils by growing oocytes. ZP proteins have an immunoglobulin-like three-dimensional structure and a ZP domain that consists of two subdomains, ZP-N and ZP-C, with ZP-N of ZP2 and ZP3 required for fibril assembly. A ZP2-ZP3 dimer is located periodically along ZP fibrils that are cross-linked by ZP1, a protein with a proline-rich N terminus. Fibrils in the inner and outer regions of the ZP are oriented perpendicular and parallel to the oolemma, respectively, giving the ZP a multilayered appearance. Upon fertilization of eggs, modification of ZP2 and ZP3 results in changes in the ZP's physical and biological properties that have important consequences. Certain structural features of ZP proteins suggest that they may be amyloid-like proteins.
Topics: Amyloidogenic Proteins; Animals; Embryo, Mammalian; Female; Gene Expression Regulation, Developmental; Humans; Oocytes; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Protein Multimerization; Zona Pellucida; Zona Pellucida Glycoproteins; Zygote
PubMed: 32569527
DOI: 10.1146/annurev-biochem-011520-105310 -
International Journal of Molecular... Feb 2020Embryo-maternal crosstalk is an important event that involves many biological processes, which must occur perfectly for pregnancy success. This complex communication... (Review)
Review
Embryo-maternal crosstalk is an important event that involves many biological processes, which must occur perfectly for pregnancy success. This complex communication starts from the zygote stage within the oviduct and continues in the uterus up to the end of pregnancy. Small extracellular vesicles (EVs) are part of this communication and carry bioactive molecules such as proteins, lipids, mRNA, and miRNA. Small EVs are present in the oviductal and uterine fluid and have important functions during fertilization and early embryonic development. Embryonic cells are able to uptake oviductal and endometrium-derived small EVs. Conversely, embryo-derived EVs might modulate oviductal and uterine function. In this review, our aim is to demonstrate the role of extracellular vesicles modulating embryo-maternal interactions during early pregnancy.
Topics: Animals; Blastocyst; Cell Communication; Endometrium; Extracellular Vesicles; Female; Humans; Oviducts; Zygote
PubMed: 32050564
DOI: 10.3390/ijms21031163