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Current Opinion in Cell Biology Jun 2020The fusion of two transcriptionally silent gametes, egg and sperm, generates a totipotent zygote that activates zygotic transcription to support further development.... (Review)
Review
The fusion of two transcriptionally silent gametes, egg and sperm, generates a totipotent zygote that activates zygotic transcription to support further development. Although the molecular details of zygotic genome activation (ZGA) are not well understood in most species, an emerging concept is that one or more pioneer transcription factors trigger zygotic transcription. Concomitantly, extensive changes in 3D chromatin organization occur during development. In this review, we discuss recent advances in understanding when and how genome architecture emerges in early metazoan embryos, how the zygotic genome is activated, and how these events might be coordinated. We also highlight some of the unknowns that may be critical to address in the future.
Topics: Animals; Chromatin; Embryonic Development; Gene Expression Regulation, Developmental; Genome; Transcription Factors; Zygote
PubMed: 32220807
DOI: 10.1016/j.ceb.2020.02.002 -
The International Journal of... 2019The oocyte GV/GVs (germinal vesicle/germinal vesicles) and zygot PN/PNs (pronucleus/pronuclei) of some mammals contain clearly visible nucleoli which exhibit an atypical... (Review)
Review
The oocyte GV/GVs (germinal vesicle/germinal vesicles) and zygot PN/PNs (pronucleus/pronuclei) of some mammals contain clearly visible nucleoli which exhibit an atypical morphological structure. These nucleoli (NCLs) can be relatively easily manipulated, i.e. removed from GVs/PNs or eventually transferred into another oocyte/zygote. Thus, with the help of micromanipulation techniques it was possible to uncover the real function(s) they play in processes of oocyte maturation and early embryonic development. The purpose of our review is to describe briefly the micromanipulation techniques that can be used for oocyte/zygote nucleoli manipulation. Moreover, we present some examples of results that were obtained in nucleolus manipulation experiments.
Topics: Animals; Cell Nucleolus; Mice; Micromanipulation; Oocytes; Parthenogenesis; Swine; Zygote
PubMed: 31058302
DOI: 10.1387/ijdb.190002mb -
Stem Cells and Development Jul 2019The mammalian zygote is described as a totipotent cell in the literature, but this characterization is elusive ignoring the molecular underpinnings. Totipotency can... (Review)
Review
The mammalian zygote is described as a totipotent cell in the literature, but this characterization is elusive ignoring the molecular underpinnings. Totipotency can connote genetic totipotency, epigenetic totipotency, or the reprogramming capacity of a cell to epigenetic totipotency. Here, the implications of these concepts are discussed in the context of the properties of the zygote. Although genetically totipotent as any diploid somatic cell is, a zygote seems not totipotent transcriptionally, epigenetically, or functionally. Yet, a zygote may retain most of the key factors from its parental oocyte to reprogram an implanted differentiated genome or the zygote genome toward totipotency. This totipotent reprogramming process may extend to blastomeres in the two-cell-stage embryo. Thus, a revised alternative model of mammalian cellular totipotency is proposed, in which an epigenetically totipotent cell exists after the major embryonic genome activation and before the separation of the first two embryonic lineages.
Topics: Animals; Cell Differentiation; Embryo, Mammalian; Epigenesis, Genetic; Gene Expression Regulation, Developmental; Humans; Zygote
PubMed: 31122174
DOI: 10.1089/scd.2019.0057 -
Trends in Genetics : TIG Nov 2016Precise elimination of maternal mRNAs plays a critical role during the maternal-to-zygotic transition (MZT) to promote developmental processing. Two new studies... (Review)
Review
Precise elimination of maternal mRNAs plays a critical role during the maternal-to-zygotic transition (MZT) to promote developmental processing. Two new studies demonstrate that, in eukaryotes, codon-mediated decay is a conserved mechanism to shape maternal mRNA stability by affecting deadenylation rate in a translation-dependent manner. These studies add to a growing body of literature suggesting that translational elongation rates are a major determinant of mRNA stability.
Topics: Codon; Eukaryota; Gene Expression Regulation, Developmental; Humans; Protein Biosynthesis; RNA Stability; RNA, Messenger; Zygote
PubMed: 27594172
DOI: 10.1016/j.tig.2016.08.007 -
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 -
International Journal of Molecular... Jan 2021The maternal-to-zygotic transition (MZT), which controls maternal signaling to synthesize zygotic gene products, promotes the preimplantation development of mouse...
The maternal-to-zygotic transition (MZT), which controls maternal signaling to synthesize zygotic gene products, promotes the preimplantation development of mouse zygotes to the two-cell stage. Our previous study reported that mouse granzyme g (Gzmg), a serine-type protease, is required for the MZT. In this study, we further identified the maternal factors that regulate the promoter activity in the zygote to the two-cell stage of mouse embryos. A full-length promoter from mouse genomic DNA, FL-p (-1696~+28 nt), was cloned, and four deletion constructs of this promoter, Δ1-p (-1369~+28 nt), Δ2-p (-939~+28 nt), Δ3-p (-711~+28 nt) and Δ4-p (-417~+28 nt), were subsequently generated. Different-sized promoters were used to perform promoter assays of mouse zygotes and two-cell stage embryos. The results showed that Δ4-p promoted the highest expression level of the enhanced green fluorescent protein (EGFP) reporter in the zygotes and two-cell embryos. The data suggested that time-specific transcription factors upregulated by binding cis-elements in the -417~+28-nt promoter region. According to the results of the promoter assay, the transcription factor binding sites were predicted and analyzed with the JASPAR database, and two transcription factors, signal transducer and activator of transcription 3 (STAT3) and GA-binding protein alpha (GABPα), were identified. Furthermore, STAT3 and GABPα are expressed and located in zygote pronuclei and two-cell nuclei were confirmed by immunofluorescence staining; however, only STAT3 was recruited to the mouse zygote pronuclei and two-cell nuclei injected with the Δ4-p reporter construct. These data indicated that STAT3 is a maternal transcription factor and may upregulate to promote the MZT. Furthermore, treatment with a STAT3 inhibitor, S3I-201, caused mouse embryonic arrest at the zygote and two-cell stages. These results suggest that STAT3, a maternal protein, is a critical transcription factor and regulates transcription activity in preimplantation mouse embryos. It plays an important role in the maternal-to-zygotic transition during early embryonic development.
Topics: Animals; Blastocyst; Cell Nucleus; Embryonic Development; Female; Gene Expression Regulation, Developmental; Granzymes; Green Fluorescent Proteins; Male; Mice; Mice, Inbred ICR; Pregnancy; Promoter Regions, Genetic; STAT3 Transcription Factor; Transcription Factors; Transcriptional Activation; Zygote
PubMed: 33466434
DOI: 10.3390/ijms22010460 -
Plant Physiology May 2016Fertilization is a general feature of eukaryotic uni- and multicellular organisms to restore a diploid genome from female and male gamete haploid genomes. In most...
Fertilization is a general feature of eukaryotic uni- and multicellular organisms to restore a diploid genome from female and male gamete haploid genomes. In most animals and fucoid algae, polyspermy block occurs at the plasmogamy step. Because the polyspermy barrier in animals and in fucoid algae is incomplete, polyspermic zygotes are generated by multiple fertilization events. However, these polyspermic zygotes with extra centrioles from multiple sperms show aberrant nuclear and cell division. In angiosperms, polyspermy block functions in the egg cell and the central cell to promote faithful double fertilization, although the mechanism of polyspermy block remains unclear. In contrast to the case in animals and fucoid algae, polyspermic zygotes formed in angiosperms are not expected to die because angiosperms lack centrosomes. However, there have been no reports on the developmental profiles of polyspermic zygotes at cellular level in angiosperms. In this study, we produced polyspermic rice zygotes by electric fusion of an egg cell with two sperm cells, and monitored their developmental profiles. Two sperm nuclei and an egg nucleus fused into a zygotic nucleus, and the triploid zygote divided into a two-celled embryo via mitotic division with a typical bipolar microtubule spindle, as observed during mitosis of a diploid zygote. The two-celled proembryos further developed and regenerated into triploid plants. These findings suggest that polyspermic plant zygotes have the potential to form triploid embryos. Polyspermy in angiosperms might be a pathway for the formation of triploid plants, which can contribute significantly to the formation of autopolyploids.
Topics: Cell Division; Cell Fusion; Cell Nucleus; Cell Nucleus Division; Chromatin; Diploidy; Fertilization; Flow Cytometry; Microtubules; Mitosis; Oryza; Seeds; Triploidy; Zygote
PubMed: 26945052
DOI: 10.1104/pp.15.01953 -
Biochemistry. Biokhimiia Dec 2015Events, manifesting transition from maternal to zygotic period of development are studied for more than 100 years, but underlying mechanisms are not yet clear. We... (Review)
Review
Events, manifesting transition from maternal to zygotic period of development are studied for more than 100 years, but underlying mechanisms are not yet clear. We provide a brief historical overview of development of concepts and explain the specific terminology used in the field. We further discuss differences and similarities between the zygotic genome activation and in vitro reprogramming process. Finally, we envision the future research directions within the field, where biochemical methods will play increasingly important role.
Topics: Animals; Embryonic Stem Cells; Gene Expression Regulation, Developmental; Genome; Humans; Zygote
PubMed: 26878577
DOI: 10.1134/S0006297915130088 -
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 -
Human Reproduction (Oxford, England) Jan 2015Does the use of a new cryoprotectant agent (CPA) exchange protocol designed to minimize osmotic stress improve oocyte or zygote vitrification by reducing sublethal...
STUDY QUESTION
Does the use of a new cryoprotectant agent (CPA) exchange protocol designed to minimize osmotic stress improve oocyte or zygote vitrification by reducing sublethal cryodamage?
SUMMARY ANSWER
The use of a new CPA exchange protocol made possible by automated microfluidics improved oocyte and zygote vitrification with superior morphology as indicated by a smoother cell surface, higher sphericity, higher cytoplasmic lipid retention, less cytoplasmic leakage and higher developmental competence compared with conventional methods.
WHAT IS KNOWN ALREADY
The use of more 'steps' of CPA exposure during the vitrification protocol increases cryosurvival and development in the bovine model. However, such an attempt to eliminate osmotic stress is limited by the practicality of performing numerous precise pipetting steps in a short amount of time.
STUDY DESIGN, SIZE, DURATION
Murine meiotically competent germinal vesicle intact oocytes and zygotes were harvested from the antral follicles in ovaries and ampulla, respectively. Bovine ovaries were obtained from a local abattoir at random stages of the estrous cycle. A total of 110 murine oocytes, 802 murine zygotes and 52 bovine oocytes were used in this study.
PARTICIPANTS/MATERIALS, SETTING, METHODS
Microfluidic devices were fabricated using conventional photo- and soft-lithography. CPAs used were 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO) for equilibration solution and 15% EG, 15% DMSO and 0.5 M sucrose for vitrification solution. End-point analyses include mathematical modeling using Kedem-Katchalsky equations, morphometrics assessed by conventional and confocal microscopy, cytoplasmic lipid quantification by nile red staining, cytoplasmic leakage quantification by fluorescent dextran intercalation and developmental competence analysis by 96 h embryo culture and blastomere quantification.
MAIN RESULTS AND THE ROLE OF CHANCE
The automated microfluidics protocol decreased the shrinkage rate of the oocyte and zygote by 13.8 times over its manual pipetting alternative. Oocytes and zygotes with a lower shrinkage rate during CPA exposure experienced less osmotic stress resulting in better morphology, higher cell quality and improved developmental competence. This microfluidic procedure resulted in murine zygotes with a significantly smoother cell surface (P < 0.001), more spherical cellular morphology (P < 0.001), increased cytoplasmic lipid retention in vitrified and warmed bovine oocytes (P < 0.01), decreased membrane perforations and cytoplasmic leakage in CPA-exposed murine zygotes (P < 0.05) and improved developmental competence of vitrified and warmed murine zygotes (P < 0.05) than CPA exposure using the current clinically used manual pipetting method.
LIMITATIONS, REASONS FOR CAUTION
It is necessary to design the microfluidic device to be more user-friendly for widespread use.
WIDER IMPLICATIONS OF THE FINDINGS
The theory and approach of eliminating osmotic stress by decreasing shrinkage rate is complementary to the prevalent osmotic stress theory in cryobiology which focuses on a minimum cell volume at which the cells shrink. The auto-microfluidic protocol described here has immediate applications for improving animal and human oocyte, zygote and embryo cryopreservation. On a fundamental level, the clear demonstration that at the same minimum cell volume, cell shrinkage rate affects sublethal damage should be broadly useful for cryobiology.
STUDY FUNDING/COMPETING INTERESTS
This project was funded by the National Institutes of Health and the University of Michigan Reproductive Sciences Program. The authors declare no conflicts of interest.
Topics: Animals; Cattle; Cryopreservation; Mice; Microfluidics; Oocytes; Osmotic Pressure; Vitrification; Zygote
PubMed: 25355589
DOI: 10.1093/humrep/deu284