Abstract:

The surge of luteinizing hormone (LH) in preovulatory ovarian follicles triggers the resumption of meiosis in oocytes and induces the proliferation of surrounding cumulus granulosa cells. It is believed that LH receptors are expressed in the mural granulosa cells, but not the oocytes and the surrounding cumulus cells, suggesting that the LH signaling is mediated by factors produced by the granulosa cells. However, the mechanism underlying oocyte maturation induced by LH before ovulation has been controversial. Current studies suggest that LH binds on to its receptor on granulosa cells of the follicular wall to promote the production of EGF-like factors, which activate various signaling cascades and induce oocyte maturation and development. Since the in vitro maturation system is difficult to simulate the in vivo physiological environment, in vitro cultured follicles are likely to be de?cient in the EGF-like factors, which could result in the poor developmental competency of in vitro cultured oocytes and restrict their efficient utilization. In this review, we summarize the EGF-like factor signaling system in granulosa cells and its regulation of oocyte maturation and development. It aims to optimize the in vitro maturation culture system of oocytes and increase the EGF-like factor signaling system in cumulus granulosa cells, thereby providing a framework for improving the efficiency on in vitro maturation of oocytes.

Key words: granulosa cells, EGF-like factor, oocyte maturation, oocyte developmental competency