Expansion of the Cumulus-Oocyte Complex During the Preovulatory Period: Possible Roles in Oocyte Maturation, Ovulation, and Fertilization

Abstract

In most mammalian species, a few thousand tightly packed and rather diminutive cells closely invest the oocyte within the antral chamber of mature ovarian follicles. Individual cells within this investing cumulus oophorus are interconnected by a vast network of gap junctions and intermediate junctions. The innermost layer of cumulus cells extend processes that penetrate the zona pellucida to make gap and intermediate junctions with the oocyte membrane, while peripheral cells at one pole of the cumulus mass are connected by gap and intermediate junctions to the innermost layer of the membrana granulosa. The cumulus oophorus, therefore, spatially intervenes between the predominant subpopulation of follicle cells (i.e., the membrana granulosa) and the maturing oocyte. All cells within the basement membrane of the follicle, including the oocyte, are thus interconnected through a gap junction network and, indeed, the unusually large number and large size of these intercellular membrane junctions probably accounts for their initial recognition and very early historical description [1]. In addition to the subpopulations of gap junctions between follicle cells, and between follicle cells and the surface of the oocyte, cumulus processes that penetrate the zona pellucida further interact with each other through extremely diminutive but numerous gap junction plaques within the substance of the zona pellucida itself, thus even more completely integrating the cellular inhabitants of the ovarian follicle [2].