Human female meiosis II occurs after fertilization with sperm
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Reference literature and anatomical texts establish that human female meiosis II (the completion of meiosis in the secondary oocyte) occurs after sperm penetration and fertilization.
<h4>Background</h4>Fertilization involves fusion between sperm and metaphase II (MII) oocyte, initiating a cascade of events including oocyte activation, resumption of meiosis, formation and interdigitation of male and female pronuclei, and zygote formation. Total Fertilization Failure (TFF), characterized by the disruption of any of these processes, occurs in 1-3% of intracytoplasmic sperm injection (ICSI) cycles. The genetic basis of TFF remains largely unexplored. TFF can occur in cases where no single genetic cause is apparent, suggesting a potential polygenic contribution.<h4>Methods</h4>A couple (34 year-old female and 35 year-old male) affected by TFF, and the mother of the affected female patient. A multi-tiered genomic, transcriptomic and functional investigation was conducted to uncover potential genetic contributors to TFF in the couple. Assisted oocyte activation (AOA) was employed upon definition of the putative genetic cause by single-oocyte RNA-seq analyses. Fertilization and embryonic development were monitored using a time-lapse incubator (EmbryoScope) to evaluate the efficiency of AOA in rescuing oocytes.<h4>Results</h4>RNA sequencing revealed aberrant expression of genes involved in meiosis, zona pellucida biogenesis, and calcium signaling. Through open-chromatin-mediated gene regulatory network (oGRN) analysis, we identified 45 transcription factors (TFs) linked to putative regulatory regions, and considered as key regulators including ZNF121, ZFP28, ZNF394, YY1, VEZF1, and SP2. Genetic analysis identified 17 transcription factors (TFs) with disrupted binding patterns to the proband's genome, associated with fertilization and early embryonic development. Gene Ontology (GO) enrichment analysis revealed that VEZF1, ZNF148, SP2, ZNF121, and ZFP28 were central regulators of key biological processes related to reproduction. Reactome pathway analysis further showed that TFAP2D, YY1, ZFP28, ZNF260, and ZNF121 were highly interconnected within critical signaling pathways, including calcium signaling, which is essential for oocyte activation and fertilization. AOA successfully rescued fertilization in 25% of oocytes, resulting in one embryo reaching the 8-cell stage.<h4>Conclusions</h4>This study integrates oocyte gene expression profiles with parental genomic data to identify transcriptional dysregulations associated with TFF. Key disruptions in gene regulatory networks and TFs binding were inferred, potentially affecting critical processes in oogenesis, fertilization, and early embryonic development. AOA by exogenous calcium administration partially rescued fertilization, highlighting its potential as a therapeutic intervention. Our genomic analyses at the single-oocyte resolution provide new insights into new potential polygenic causes of TFF.
Instead, the cytoplasm is divided unequally, and one daughter cell is much larger than the other. This larger cell, the secondary oocyte, eventually leaves the ovary during ovulation. The smaller cell, called the first polar body, may or may not complete meiosis and produce second polar bodies; in either case, it eventually disintegrates. Therefore, even though oogenesis produces up to four cells, only one survives. How does the diploid secondary oocyte become an ovum—the haploid female gamete? Meiosis of a secondary oocyte is completed only if a sperm succeeds in penetrating its barriers. Meiosis II then resumes, producing one haploid ovum that, at the instant of fertilization by a (haploid) sperm, becomes the first diploid cell of the new offspring (a zygote). Thus, the ovum can be thought of as a brief, transitional, haploid stage between the diploid oocyte and diploid zygote. The larger amount of cytoplasm contained in the female gamete is used to supply the developing zygote with nutrients during the period between fertilization and implantation into the uterus. Interestingly, sperm contribute only DNA at fertilization —not cytoplasm.
meiosis, after fertilization has occurred. Other differences between male and female meiosis are … into the genome, since gene transfer after fertilization cannot be detected. Recent modifications … of Mullerian duct structures interfering with sperm transfer into the female, and Leydig cell
and the secondary oocyte completes meiosis II only after fertilization. All of the polar bodies eventually … Multicellular Organisms 2.7 hours after fertilization 3.5 hours after fertilization other sites, under the control … recognition mechanism. A second discrimination step occurs after the amino acid has been covalently linked to
sperm or egg cells, although in mammals the process of meiosis finishes only after fertilization so the product is a zygote. It involves two rounds of
Meiosis ( ) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes; the sperm or egg cells, although in mammals the process of meiosis finishes only after fertilization so the product is a zygote. It involves two rounds of division that ultimately result in four cells, each with only one copy of each chromosome (haploid). Additionally, prior to
Meiosis ( ) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes; the sperm or egg cells, although in mammals the process of meiosis finishes only after fertilization so the product is a zygote. It involves two rounds of division that ultimately result in four cells, each with only one copy of each chromosome (haploid).…
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