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Genetics Oct 2021Embryonic patterning is critically dependent on zygotic genome activation (ZGA). In Drosophila melanogaster embryos, the pioneer factor Zelda directs ZGA, possibly in...
Embryonic patterning is critically dependent on zygotic genome activation (ZGA). In Drosophila melanogaster embryos, the pioneer factor Zelda directs ZGA, possibly in conjunction with other factors. Here, we have explored the novel involvement of Chromatin-Linked Adapter for MSL Proteins (CLAMP) during ZGA. CLAMP binds thousands of sites genome-wide throughout early embryogenesis. Interestingly, CLAMP relocates to target promoter sequences across the genome when ZGA is initiated. Although there is a considerable overlap between CLAMP and Zelda binding sites, the proteins display distinct temporal dynamics. To assess whether CLAMP occupancy affects gene expression, we analyzed transcriptomes of embryos zygotically compromised for either clamp or zelda and found that transcript levels of many zygotically activated genes are similarly affected. Importantly, compromising either clamp or zelda disrupted the expression of critical segmentation and sex determination genes bound by CLAMP (and Zelda). Furthermore, clamp knockdown embryos recapitulate other phenotypes observed in Zelda-depleted embryos, including nuclear division defects, centrosome aberrations, and a disorganized actomyosin network. Based on these data, we propose that CLAMP acts in concert with Zelda to regulate early zygotic transcription.
Topics: Animals; Binding Sites; DNA-Binding Proteins; Drosophila Proteins; Drosophila melanogaster; Gene Expression Regulation, Developmental; Nuclear Proteins; Protein Binding; Zygote
PubMed: 34849887
DOI: 10.1093/genetics/iyab107 -
Journal of Experimental Botany Jun 2010In angiosperms, a zygote generally divides into a two-celled proembryo consisting of an apical and a basal cell that possess different cell fates. This first division of...
In angiosperms, a zygote generally divides into a two-celled proembryo consisting of an apical and a basal cell that possess different cell fates. This first division of the zygote is a putative step in the formation of the apical-basal axis of the proembryo. The gamete fusion activates the egg, and the gamete fusion site on the zygote has been reported to provide a possible cue for subsequent zygotic development and/or embryonic patterning in animals and plants. In this study, the gamete fusion site on the rice zygote was labelled by in vitro fertilization of a rice egg cell with a fluorescence-stained sperm cell. The positional relationship between the gamete fusion site and the division plane formed by zygotic cleavage was monitored using a fixed culture of the fusion site-labelled zygote until the two-celled proembryo stage. The results indicate that gamete fusion sites exist on two-celled proembryos with no relation to the position of the first division plane, and that the gamete fusion site on the rice zygote does not function as a determinant for positioning the zygote division plane.
Topics: Cell Division; Cell Fusion; Germ Cells, Plant; Oryza; Zygote
PubMed: 20462944
DOI: 10.1093/jxb/erq131 -
The International Journal of... 2008Global demethylation of DNA which marks the onset of development occurs asynchronously in the mouse; paternal DNA is demethylated at the the zygote stage, whereas...
Global demethylation of DNA which marks the onset of development occurs asynchronously in the mouse; paternal DNA is demethylated at the the zygote stage, whereas maternal DNA is demethylated later in development. The biological function of such asymmetry and its underlying mechanisms are currently unknown. To test the hypothesis that the early demethylation of male DNA may be associated with protamine-histone exchange, we ,used round spermatids, whose DNA is still associated with histones, for artificial fertilization (round spermatid injection or ROSI), and compared the level of methylation of metaphase chromosomes in the resulting zygotes with the level of methylation in zygotes obtained after fertilization using mature sperm heads (intracytoplasmic sperm injection or ICSI). In contrast to ICSI-derived zygotes, ROSI-derived zygotes possessed only slightly demethylated paternal DNA. Both types of zygotes developed to term with similar rates which shows that hypomethylation of paternal DNA at the zygotic metaphase is not essential for full development in mice. Incorporation of exogenously expressed histone H2BYFP into paternal pronuclei was significantly higher in ICSI-derived zygotes than in ROSI-derived zygotes. Surprisingly, in the latter the incorporation of histone H2BYFP into the paternal pronucleus was still significantly higher than into the maternal pronucleus, suggesting that some exchange of chromatin-associated proteins occurs not only after ICSI but also after ROSI. This may explain why after ROSI, some transient demethylation of paternal DNA occurs early after fertilization, thus providing support for the hypothesis regarding the link between paternal DNA demethylation and protamine/histone exchange.
Topics: Animals; Cell Nucleus; DNA; DNA Methylation; Female; Fertilization; Fertilization in Vitro; Histones; Male; Mice; Mice, Inbred C57BL; Protamines; Sperm Head; Sperm Injections, Intracytoplasmic; Spermatozoa; Zygote
PubMed: 18311720
DOI: 10.1387/ijdb.072347zp -
Human Reproduction (Oxford, England) Feb 2006Preliminary observations revealed that advanced zygotes of the PO strain mouse are often bilaterally symmetrical, and suggested that both the plane of first cleavage and...
BACKGROUND
Preliminary observations revealed that advanced zygotes of the PO strain mouse are often bilaterally symmetrical, and suggested that both the plane of first cleavage and features of the blastocyst bear a consistent relationship to the zygote's bilateral plane.
METHODS
Spaced oil drops were injected into the zona pellucida to delineate the bilateral plane in pronuclear zygotes, and a distinct cluster of drops then placed over the second polar body. Such non-invasive marking was combined with gelation of the perivitelline space to prevent rotation of the zygotes within the zona pellucida.
RESULTS
Nearly two-thirds of advanced pronuclear stage zygotes were bilaterally symmetrical and, regardless of whether first cleavage was meridional, it was almost invariably orthogonal to the bilateral plane. Moreover, both the axis of polarity and bilateral plane of the blastocyst bore a consistent relationship to the zygote's bilateral plane. Haploid parthenotes also exhibited bilateral symmetry, although in the absence of fertilization, first cleavage was less consistently orthogonal to the bilateral plane.
CONCLUSIONS
Bilateral symmetry may be an intrinsic property of the oocyte that is induced by its activation and, from the reproducible way it maps on both the 2-cell conceptus and blastocyst, seems to play a role in early patterning.
Topics: Animals; Blastocyst; Body Patterning; Cell Nucleus; Cell Shape; Cleavage Stage, Ovum; Embryonic Development; Mice; Models, Biological; Zygote
PubMed: 16210387
DOI: 10.1093/humrep/dei318 -
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 -
Reproduction, Nutrition, Development 2001Despite the attention paid to culture media, the relevance of the handling medium at egg recovery/transfer is frequently overlooked. In the present work, we compare the... (Comparative Study)
Comparative Study
Despite the attention paid to culture media, the relevance of the handling medium at egg recovery/transfer is frequently overlooked. In the present work, we compare the effect of two different handling media (PBS and HEPES-buffered Ham F10, both supplemented with 20% (v/v) FCS), upon in vitro and in vivo developmental ability of in vivo fertilised rabbit zygotes. Zygotes recovered in HEPES-buffered medium (permanence 1 h as maximum) and subsequently cultured in vitro developed more efficiently to the compacted morula (100%) and blastocyst stage (92%) than those recovered in PBS (83% and 76%, respectively, P < 0.05). Zygotes recovered in such media were then further bilaterally transferred to recipient does following a brief in vitro culture period (for 4 hours). At caesarean section (day 28 of pregnancy), significant differences were observed in both the percentage of pregnant uterine horns (PBS: 60% vs. HEPES-buffered Ham F10: 100%) and live birth rates (PBS: 14% vs. HEPES-buffered Ham F10: 34%). Thus when early rabbit zygotes must be handled, even for short incubation periods, the medium is not innocuous.
Topics: Animals; Culture Media; Culture Techniques; Embryo Transfer; Female; Pregnancy; Rabbits; Zygote
PubMed: 11434521
DOI: 10.1051/rnd:2001121 -
Human Reproduction Update 2002The maternal to zygotic transition is the first major transition that occurs following fertilization, and entails a dramatic reprogramming of gene expression that is... (Review)
Review
The maternal to zygotic transition is the first major transition that occurs following fertilization, and entails a dramatic reprogramming of gene expression that is essential for continued development. Although the major reprogramming of gene expression occurs during the 2-cell stage, transcription is evident in the 1-cell embryo, with the male pronucleus supporting a significantly higher level of transcription than the female pronucleus. This difference is likely due to differences in chromatin structure as a consequence of the protamine-histone exchange. Although the 1-cell embryo is transcriptionally competent, transcription and translation appear uncoupled. This transcription, however, may mark promoters for efficient utilization in the 2-cell embryo. Genome activation in the 2-cell embryo is accompanied by a requirement for an enhancer for efficient transcription and the more efficient utilization of TATA-less promoters. These changes in promoter utilization could contribute substantially to the reprogramming of gene expression. Superimposed on genome activation is the development of a chromatin-mediated transcriptionally repressive state that is relieved by either inducing histone hyperacetylation or inhibiting the second round of DNA replication. Since genome activation appears to be a relatively opportunistic process, the development of the transcriptionally repressive state may be a major determinant in establishing the appropriate gene expression profile that is essential for continued development.
Topics: Animals; Blastocyst; Embryonic and Fetal Development; Female; Fertilization; Gene Expression Regulation, Developmental; Mammals; Morphogenesis; Zygote
PubMed: 12206467
DOI: 10.1093/humupd/8.4.323 -
Genome Biology Mar 2024Early embryonic developmental programs are guided by the coordinated interplay between maternally inherited and zygotically manufactured RNAs and proteins. Although...
BACKGROUND
Early embryonic developmental programs are guided by the coordinated interplay between maternally inherited and zygotically manufactured RNAs and proteins. Although these processes happen concomitantly and affecting gene function during this period is bound to affect both pools of mRNAs, it has been challenging to study their expression dynamics separately.
RESULTS
By employing SLAM-seq, a nascent mRNA labeling transcriptomic approach, in a developmental time series we observe that over half of the early zebrafish embryo transcriptome consists of maternal-zygotic genes, emphasizing their pivotal role in early embryogenesis. We provide an hourly resolution of de novo transcriptional activation events and follow nascent mRNA trajectories, finding that most de novo transcriptional events are stable throughout this period. Additionally, by blocking microRNA-430 function, a key post transcriptional regulator during zebrafish embryogenesis, we directly show that it destabilizes hundreds of de novo transcribed mRNAs from pure zygotic as well as maternal-zygotic genes. This unveils a novel miR-430 function during embryogenesis, fine-tuning zygotic gene expression.
CONCLUSION
These insights into zebrafish early embryo transcriptome dynamics emphasize the significance of post-transcriptional regulators in zygotic genome activation. The findings pave the way for future investigations into the coordinated interplay between transcriptional and post-transcriptional landscapes required for the establishment of animal cell identities and functions.
Topics: Animals; Zebrafish; RNA, Messenger; Zygote; Embryonic Development; MicroRNAs; Gene Expression Regulation, Developmental
PubMed: 38504288
DOI: 10.1186/s13059-024-03197-8 -
Methods in Molecular Biology (Clifton,... 2019The CRISPR-Cas9 system in bacteria and archaea has recently been exploited for genome editing in various model organisms, including the mice. In this scheme, components...
The CRISPR-Cas9 system in bacteria and archaea has recently been exploited for genome editing in various model organisms, including the mice. In this scheme, components of the CRISPR-Cas9 system are delivered into the mouse zygote and mutant mice carrying genetic modifications derived. Although microinjection has been the technology of choice, electroporation has also emerged and been proven to be effective delivering CRISPR-Cas9 reagents into the mouse zygote. Here, we describe the experimental protocol employing electroporation to deliver CRISPR-Cas9 reagents into mouse embryos and derive gene-edited mutant mice.
Topics: Animals; CRISPR-Cas Systems; Electroporation; Female; Gene Editing; Mice; Mutation; Zygote
PubMed: 30353514
DOI: 10.1007/978-1-4939-8831-0_10 -
Human Genetics Feb 1992Chromosome errors, inherited or arising de novo during gametogenesis and transmitted at fertilization to the conceptus, may be a major cause of embryonic mortality. The... (Review)
Review
Chromosome errors, inherited or arising de novo during gametogenesis and transmitted at fertilization to the conceptus, may be a major cause of embryonic mortality. The in vitro fertilization and embryo transfer (IVF/ET) procedure provides extra material--oocytes, zygotes, and embryos--to investigate the contribution of chromosomal abnormality to implantation failure. This paper reviews the results of cytogenetic studies on such material. Estimates from a total of 1120 oocytes from 11 studies give an overall proportion of chromosomal abnormality of 35%. Single and multiple nullisomies and disomies are found, involving nonrandom chromosome gain or loss. Hypohaploid complements are more frequent than hyperhaploid complements. The higher rate of chromosome loss of hypohaploid karyotypes was found to be largely artifactual. The estimated overall frequency of aneuploidy is 13%. In embryos the level of chromosomal abnormality is 23%-40%. Errors of fertilization are responsible for a substantial number of triploid embryos, many of which develop into mosaics. Factors extrinsic to the conceptus, such as infertility, advanced maternal age, and ovarian hyperstimulation, may increase the level of chromosomal abnormality. More refined methods for accurately recognizing and selecting chromosomally normal embryos for transfer are needed to improve the success rate of this reproductive technology.
Topics: Adult; Cytogenetics; Embryo, Mammalian; Female; Fertilization in Vitro; Humans; Male; Maternal Age; Oocytes; Ploidies; Pregnancy; Pregnancy, High-Risk; Zygote
PubMed: 1740312
DOI: 10.1007/BF00215667