Meiotic cell cycle arrest in mammalian oocytes

Abstract

Meiotic cell cycle in mammalian oocytes is a dynamic process that involves several stop/go channels. The cell cycle arrest in oocyte occurs at various stages such as diplotene, metaphase-I (M-I), metaphase-II (M-II), and so called metaphase-like arrest (M-III). Leutinizing hormone surge induces meiotic resumption from diplotene arrest in follicular microenvironment by overriding several factors responsible for the maintenance of meiotic arrest. The inhibitory factors are synthesized in oocyte or in the associated follicular somatic cells and transferred to the oocyte. The major factors include hypoxanthine, cyclic adenosine 3', 5'-monophosphate, cyclic guanosine 3', 5'-monophosphate, reactive oxygen species, protein kinase A, and protein kinase C. In the presence of active protein kinases, epidermal-like growth factors are produced that activate mitogen-activated protein kinase in cumulus granulosa cells. The maturation promoting factor, cytostatic factors, and spindle assembly checkpoint proteins are also involved in that maintenance of arrest at various stages of meiotic cell cycle in mammalian oocytes. In this review, we briefly summarize the role of these factors in the maintenance of meiotic cell cycle arrest in mammalian oocytes.

An insufficient increase of cytosolic free calcium level results postovulatory aging-induced abortive spontaneous egg activation in rat

“…An increase of cytosolic free Ca 2+ (due to burst from internal stores) induces EA during fertilization [5,38,39]. Further, CI increases cytosolic free Ca 2+ level [35] and induces EA in several mammalian species [11,14,16,32,[40][41][42].…”

Single Ca2+ transients vs oscillatory Ca2+ signaling for assisted oocyte activation: limitations and benefits

“…IP3 binds to its cognate receptor (IP3R) embedded on the endoplasmic reticulum (ER), resulting in the opening of Ca 2+ -permeable channels that facilitate Ca 2+ release from intracellular stores, thereby increase concentrations of free cytoplasmic Ca 2+ (Miyazaki et al 1992). Subsequently, a signaling cascade is activated to alleviate meiotic arrest, which is secured by high levels of M-phase promoting factor (MPF) (Tripathi et al 2010). Interestingly, species that physiologically undergo Ca 2+ oscillations during oocyte activation are also capable of responding to a single Ca 2+ transient, for instance, as induced by Ca 2+ ionophores or ethanol during assisted oocyte activation (AOA).…”

Metabolism throughout follicle and oocyte development in mammals

“…Oocyte maturation is comprised of both, nuclear and cytoplasmic maturation, and both must be completed for the gamete to acquire developmental competence (Eppig, 1996). Nuclear maturation consists of the nuclear changes associated with the resumption of meiosis I (germinal vesicle breakdown (GVBD), progression to metaphase II (MII) and extrusion of the first polar body, and arrest at MII (for a review see (Tripathi et al, (2010)). In contrast, cytoplasmic maturation comprises the acquisition of mechanisms for sperm penetration and polyspermy block, calcium release and exocytosis of cortical granules, decondensation of the sperm chromatin, pronuclei formation, and support of the first embryonic divisions (Ajduk et al, 2008;Ferreira et al, 2009).…”