Physiological and pathological mechanisms of oocyte meiosis.

Normal oogenesis is crucial to successful reproduction. During the human female fetal stage, primordial germ cells transform from mitosis to meiosis. After synapsis and recombination of homologous chromosomes, meiosis is arrested at the diplotene stage of prophase in meiosis I. The maintenance of oocyte meiotic arrest in the follicle is primarily attributed to high cytoplasmic concentrations of cyclic adenosine monophosphate. During the menstrual cycle, follicle-stimulating hormone and luteinizing hormone lead to the resumption of meiosis that occurs in certain oocytes and complete the ovulation process. Anything that disturbs oocyte meiosis may result in failure of oogenesis and seriously affect both the fertilization and embryonic development. The rapid development of the assisted reproduction technology, high-throughput sequencing technology, and molecular biology technology provide new ideas and means for human to understand molecular mechanism of meiosis and diagnosis and treatment of oocyte maturation defects. In this review, we mainly summarize the recent physiological and pathological mechanisms of oogenesis, involving homologous recombination, meiotic arrest and resumption, maternal mRNA degradation, post-translational regulation, zona pellucida assembly, and so on. We wish to take this opportunity to raise the awareness of researchers in related fields on oocyte meiosis, providing a theoretical basis for further research and disease treatments.