Paracrine actions of oocytes in the mouse pre-ovulatory follicle

In mammals, ovulation requires a tight control of extracellular matrix modifications, within both the follicle wall and the inner mass of granulosa cells surrounding the oocyte, namely the cumulus cells. During the pre-ovulatory period, mural granulosa cells promote selective degradation of perifollicular matrix, resulting in the formation of a follicle rupture site. Conversely, cumulus cells synthesize a large amount of a muco-elastic matrix that plays an essential role in the extrusion of the oocyte from the follicle and in the subsequent fertilization process. Formation of such matrix by cumulus cells in the pre-ovulatory follicle appears to be controlled by a paracrine influence by the oocyte. We have shown that mouse oocytes modulate the response of cumulus cells to an ovulatory gonadotropin stimulus by promoting the synthesis and preventing the degradation of cumulus matrix. Therefore, although gonadotropins are essential for triggering the complex events involved in ovulation, the oocyte appears to have an active role in this process. In the present review current data and hypotheses concerning molecular mechanisms involved in the organization and synthesis of cumulus matrix are discussed.