Controlling meiotic resumption in bovine oocytes: A review

Abstract

Meiotic arrest refers to the nuclear stage of the oocytes within the follicles. Meiotic resumption occurs when oocytes are isolated from their follicular environment and placed in a simple maturation medium. The sine qua none condition for meiotic resumption is that the oocytes must be competent to resume meiosis. It has been shown that competent oocytes must reach a minimum diameter before been able to resume meiosis. In the bovine, competent oocytes measure at least 110 μm in diameter (24, 39). It appears that the inhibitory factors of meiotic resumption might only be necessary after the oocyte has acquired its competence. However, once the oocytes become competent, they need these factors to maintain meiotic arrest. It is generally recognized that follicular cells produce inhibitors necessary to maintain the oocyte in meiotic arrest. The removal of the oocyte from its follicular environment deprives the oocyte of inhibitory factors. Oocytes then resume meiosis (63). This article will first review the different chemical modulators to emphasize the importance of protein synthesis and the role of different kinases and phosphatases. Then it will review the follicular aspects involved in the control of meiotic arrest of oocytes competent to resume meiosis.