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Reproduction (Cambridge, England) Aug 2019The mammalian zygote is a totipotent cell that generates all the cells of a new organism through embryonic development. However, if one asks about the totipotency of... (Review)
Review
The mammalian zygote is a totipotent cell that generates all the cells of a new organism through embryonic development. However, if one asks about the totipotency of blastomeres after one or two zygotic divisions, opinions differ. As it is impossible to determine the individual developmental potency of early blastomeres in an intact embryo, experiments of blastomere isolation were conducted in various species, showing that two-cell blastomeres could give rise to a new organism when sister cells were separated. A mainstream interpretation was that each of the sister mammalian blastomeres was equally totipotent. However, reevaluation of those experiments raised some doubts about the real prevalence of cases in which this interpretation could truly be validated. We compiled experiments that tested the individual developmental potency of early mammalian blastomeres in a cell-autonomous way (i.e. excluding nuclear transfer and chimera production). We then confronted the developmental abilities with reported molecular differences between sister blastomeres. The reevaluated observations were at odds with the mainstream view: A viable two-cell embryo can already include one non-totipotent blastomere. We were, thus, led to propose a revised model for totipotency continuity based on the construction of the zygote as a mosaic, which accounts for differential inheritance of totipotency-relevant components between sister blastomeres. This takes place with no preordained mechanisms that would ensure a reproducible partition. This model, which is compatible with the body of data on regulative properties of mammalian early embryos, aims at tempering the rigid interpretation that discounted maternal constraints on totipotency.
Topics: Animals; Blastomeres; Humans; Models, Biological; Mosaicism; Zygote
PubMed: 30978695
DOI: 10.1530/REP-18-0462 -
Cell and Tissue Research Jan 2016The origin recognition complex (ORC) proteins, ORC1-6, are the first known proteins that bind DNA replication origins to mark the competency for the initiation of DNA... (Review)
Review
The origin recognition complex (ORC) proteins, ORC1-6, are the first known proteins that bind DNA replication origins to mark the competency for the initiation of DNA synthesis. These proteins have complex mechanisms of assembly into the ORC complex and unexpected localizations in the mitotic chromosomes, cytoplasm, and nuclear structures. The mammalian zygote is a potentially important model that may contribute to our understanding of the mechanisms and features influencing origin establishment and in the identification of other functions of the ORC proteins. Together with expected localizations to the chromatin during G1, we found an unexpected distribution in the cytoplasm that appeared to accumulate ORC proteins suggesting potential roles for ORC subunits in mitosis and chromatin segregation. ORC1, 2, 3, and 5 all localize to the area between the separating maternal chromosomes shortly after fertilization. ORC4 forms a cage around the set of chromosomes that will be extruded during polar body formation before it binds to the chromatin shortly before zygotic DNA replication. These data suggest that the ORC proteins may also play roles in preparing the cell for DNA replication in addition to their direct role in establishing functional replication origins.
Topics: Animals; DNA Replication; Female; Humans; Male; Origin Recognition Complex; Spermatozoa; Zygote
PubMed: 26453397
DOI: 10.1007/s00441-015-2296-3 -
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 -
Molecular Aspects of Medicine Oct 2013Prior to activation of the embryonic genome, the initiating events of mammalian development are under maternal control and include fertilization, the block to polyspermy... (Review)
Review
Prior to activation of the embryonic genome, the initiating events of mammalian development are under maternal control and include fertilization, the block to polyspermy and processing sperm DNA. Following gamete union, the transcriptionally inert sperm DNA is repackaged into the male pronucleus which fuses with the female pronucleus to form a 1-cell zygote. Embryonic transcription begins during the maternal to zygotic transfer of control in directing development. This transition occurs at species-specific times after one or several rounds of blastomere cleavage and is essential for normal development. However, even after activation of the embryonic genome, successful development relies on stored maternal components without which embryos fail to progress beyond initial cell divisions. Better understanding of the molecular basis of maternal to zygotic transition including fertilization, the activation of the embryonic genome and cleavage-stage development will provide insight into early human development that should translate into clinical applications for regenerative medicine and assisted reproductive technologies.
Topics: Animals; DNA Methylation; Embryonic Development; Female; Fertilization; Genome; Humans; Male; Mammals; Mice; Reproductive Techniques, Assisted; Spermatozoa; Transcription, Genetic; Zygote
PubMed: 23352575
DOI: 10.1016/j.mam.2013.01.003 -
BioEssays : News and Reviews in... Apr 2017Zygote cytokinesis produces two symmetric blastomeres, which contain one copy of each parental genome. Contrary to this dogma, we recently discovered that mammalian... (Review)
Review
Zygote cytokinesis produces two symmetric blastomeres, which contain one copy of each parental genome. Contrary to this dogma, we recently discovered that mammalian zygotes can spontaneously segregate entire parental genomes into different blastomeres and coined this novel form of genome segregation heterogoneic division. The molecular mechanisms underlying the emergence of blastomeres with different parental genomes during the first mitotic cycle remain to be elucidated. Here, we speculate on which parental genome asymmetries could provide a mechanistic foundation for these remarkable zygote divisions. In reviewing the field and considering our findings, we revisit the architecture of the first zygotic metaphase by invoking asymmetric interactions between the mitotic spindle and the parental kinetochores. We also speculate on how asynchronous parental cell cycles can be a source of heterogoneic zygote divisions through the formation of parental genome private spindles.
Topics: Animals; Blastomeres; Chromosome Segregation; Genome; Humans; Mitosis; Spindle Apparatus; Zygote
PubMed: 28247957
DOI: 10.1002/bies.201600226 -
Journal of Plant Research May 2017Fertilization is a general feature of eukaryotic uni- and multicellular organisms to restore a diploid genome from female and male gamete haploid genomes. In... (Review)
Review
Fertilization is a general feature of eukaryotic uni- and multicellular organisms to restore a diploid genome from female and male gamete haploid genomes. In angiosperms, polyploidization is a common phenomenon, and polyploidy would have played a major role in the long-term diversification and evolutionary success of plants. As for the mechanism of formation of autotetraploid plants, the triploid-bridge pathway, crossing between triploid and diploid plants, is considered as a major pathway. For the emergence of triploid plants, fusion of an unreduced gamete with a reduced gamete is generally accepted. In addition, the possibility of polyspermy has been proposed for maize, wheat and some orchids, although it has been regarded as an uncommon mechanism of triploid formation. One of the reasons why polyspermy is regarded as uncommon is because it is difficult to reproduce the polyspermy situation in zygotes and to analyze the developmental profiles of polyspermic triploid zygotes. Recently, polyspermic rice zygotes were successfully produced by electric fusion of an egg cell with two sperm cells, and their developmental profiles were monitored. Two sperm nuclei and an egg nucleus fused into a zygotic nucleus in the polyspermic zygote, and the triploid zygote divided into a two-celled embryo via mitotic division with a typical bipolar microtubule spindle. The two-celled proembryos further developed and regenerated into triploid plants. These suggest that polyspermic plant zygotes have the potential to form triploid embryos, and that polyspermy in angiosperms might be a pathway for the formation of triploid plants.
Topics: Animals; Cell Division; Cell Fusion; Cell Nucleus; Chromosome Segregation; Diploidy; Female; Fertilization; Magnoliopsida; Male; Microtubules; Orchidaceae; Oryza; Plant Physiological Phenomena; Polyploidy; Seeds; Triploidy; Triticum; Zea mays; Zygote
PubMed: 28275885
DOI: 10.1007/s10265-017-0913-9 -
Methods in Molecular Biology (Clifton,... 2020The CRISPR/Cas9 system is a powerful tool for generation of genetically modified mice. In conventional protocols, Cas9 protein (or mRNA) and sgRNA are introduced into...
The CRISPR/Cas9 system is a powerful tool for generation of genetically modified mice. In conventional protocols, Cas9 protein (or mRNA) and sgRNA are introduced into zygotes by microinjection. However, microinjection requires special skill and is too time-consuming to treat zygotes on a large scale. Recently, we have developed a simple electroporation method which generates genetically modified mice with high efficiency. Here, we describe our method GEEP (genome editing by electroporation of Cas9 protein). This method facilitates high-throughput genetic analysis of the mouse. This chapter describes the GEEP method to generate genetically modified mice.
Topics: Animals; Animals, Genetically Modified; CRISPR-Associated Protein 9; CRISPR-Cas Systems; Electroporation; Female; Male; Mice; RNA, Guide, CRISPR-Cas Systems; Zygote
PubMed: 31468486
DOI: 10.1007/978-1-4939-9740-4_13 -
STAR Protocols Sep 2021It is often necessary to learn whether macromolecules occupy a fixed place in cells. This protocol makes it possible to learn whether individual nucleolar proteins in...
It is often necessary to learn whether macromolecules occupy a fixed place in cells. This protocol makes it possible to learn whether individual nucleolar proteins in remain in place or depart from and return to the nucleolus. The protocol uses early zygotes in which parental nucleoli are separate for at least one hour. The protocol demonstrates that the localization of many nucleolar proteins is in fact highly dynamic. Photobleaching is not required. For complete details on the use and execution of this protocol, please refer to Tartakoff et al. (2021).
Topics: Cell Nucleolus; Cytological Techniques; Nuclear Proteins; Saccharomyces cerevisiae; Zygote
PubMed: 34430911
DOI: 10.1016/j.xpro.2021.100736 -
Reproduction (Cambridge, England) Dec 2016Gametogenesis (spermatogenesis and oogenesis) is accompanied by the acquisition of gender-specific epigenetic marks, such as DNA methylation, histone modifications and... (Review)
Review
Gametogenesis (spermatogenesis and oogenesis) is accompanied by the acquisition of gender-specific epigenetic marks, such as DNA methylation, histone modifications and regulation by small RNAs, to form highly differentiated, but transcriptionally silent cell-types in preparation for fertilisation. Upon fertilisation, extensive global epigenetic reprogramming takes place to remove the previously acquired epigenetic marks and produce totipotent zygotic states. It is the aim of this review to delineate the cellular and molecular events involved in maternal, paternal and zygotic epigenetic reprogramming from the time of gametogenesis, through fertilisation, to the initiation of zygotic genome activation for preimplantation embryonic development. Recent studies have begun to uncover the indispensable functions of epigenetic players during gametogenesis, fertilisation and preimplantation embryo development, and a more comprehensive understanding of these early events will be informative for increasing pregnancy success rates, adding particular value to assisted fertility programmes.
Topics: Animals; Cellular Reprogramming; Epigenesis, Genetic; Gene Expression Regulation, Developmental; Humans; Male; Mice; Zygote
PubMed: 27601712
DOI: 10.1530/REP-16-0376 -
Science Advances Feb 2022Translational regulation plays an important role in gene expression and function. Although the transcriptional dynamics of mouse preimplantation embryos have been well...
Translational regulation plays an important role in gene expression and function. Although the transcriptional dynamics of mouse preimplantation embryos have been well characterized, the global mRNA translation landscape and the master regulators of zygotic genome activation (ZGA) remain unknown. Here, by developing and applying a low-input ribosome profiling (LiRibo-seq) technique, we profiled the mRNA translation landscape in mouse preimplantation embryos and revealed the translational dynamics during mouse preimplantation development. We identified a marked translational transition from MII oocytes to zygotes and demonstrated that active translation of maternal mRNAs is essential for maternal-to-zygotic transition (MZT). We further showed that two maternal factors, Smarcd2 and Cyclin T2, whose translation is activated in zygotes, are required for chromatin reprogramming and ZGA, respectively. Our study thus not only filled in a knowledge gap on translational regulation during mammalian preimplantation development but also revealed insights into the critical function of maternal mRNA translation in MZT.
Topics: Animals; Embryonic Development; Gene Expression Regulation, Developmental; Mammals; Mice; Protein Biosynthesis; RNA, Messenger, Stored; Zygote
PubMed: 35108058
DOI: 10.1126/sciadv.abj3967