The art of oocyte meiotic arrest regulation

Abstract

A central dogma of mammalian reproductive biology is that the size of the primordial follicle pool represents reproductive capacity in females. The assembly of the primordial follicle starts after the primordial germ cells (PGCs)-derived oocyte releases from the synchronously dividing germline cysts. PGCs initiate meiosis during fetal development. However, after synapsis and recombination of homologous chromosomes, they arrest at the diplotene stage of the first meiotic prophase (MI). The diplotene-arrested oocyte, together with the surrounding of a single layer of flattened granulosa cells, forms a basic unit of the ovary, the primordial follicle. At the start of each estrous (animal) or menstrual cycle (human), in response to a surge of luteinizing hormone (LH) from the pituitary gland, a limited number of primordial follicles are triggered to develop into primary follicles, preantral follicles, antral follicles and reach to preovulatory follicle stage. During the transition from the preantral to antral stages, the enclosed oocyte gradually acquires the capacity to resume meiosis. Meiotic resumption from the prophase of MI is morphologically characterized by the dissolution of the oocyte nuclear envelope, which is generally termed the “germinal vesicle breakdown” (GVBD). Following GVBD and completion of MI, the oocyte enters meiosis II without an obvious S-phase and arrests at metaphase phase II (MII) until fertilization. The underlying mechanism of meiotic arrest has been widely explored in numerous studies. Many studies indicated that two cellular second messengers, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) play an essential role in maintaining oocyte meiotic arrest. This review will discuss how these two cyclic nucleotides regulate oocyte maturation by blocking or initiating meiotic processes, and to provide an insight in future research.

Signalling pathways and mechanistic cues highlighted by transcriptomic analysis of primordial, primary, and secondary ovarian follicles in domestic cat

“…H1T is the first variant to be expressed in meiotic spermatocytes, the presence in later germ cell stage up to elongated spermatids seems to be species-specific 80 . The dormant PrFs are arrested in meiosis I 83 and primary spermatocytes are in prophase of meiosis I 84 . It could be possible that H1T fulfils a specific function during this cell division phase, for example, on chromatin structure.…”

Identification of Chromatin Accessibility During The Early Stage of Pig SCNT Embryo Reprogramming by ATAC-Seq

“…We also found that the accessible chromatin in oocytes and embryos both involved PDE activity, which degraded cAMP, and high levels of cAMP are related to the inhibition of meiosis [38,39]. The PA and SCNT embryos had recently completed meiosis, and this chromatin open site may be inherited from the M2 oocyte.…”

Tissue Engineered Ovary

“…In the ovary, the primordial germ cells, now referred to as gonocytes, are surrounded by pre-granulosa cells to create nests of synchronously dividing germ cells. After initiation of meiosis and recombination of homologous chromosomes, the oocytes arrests in the diplotene I stage (Pan and Li 2019). The support cells invade the nests and primordial follicles are formed with a single centralized oocyte and squamous granulosa cells, which occurs between 15 and 22 weeks of gestation in humans (Maheshwari and Fowler 2008).…”

“…The support cells invade the nests and primordial follicles are formed with a single centralized oocyte and squamous granulosa cells, which occurs between 15 and 22 weeks of gestation in humans (Maheshwari and Fowler 2008). This meiotic arrest is maintained by high levels of cAMP produced by the surrounding granulosa cells (Pan and Li 2019). The primordial follicle pool represents the finite source of potential egg cells and finite source of ovarian hormones for that individual.…”