Paracrine actions of oocytes in the mouse pre-ovulatory follicle

In mammals, ovulation requires a tight control of extracellular matrix modi fications, within both the follicle wall and the inner mass of granulosa ce lls surrounding the oocyte. namely the cumulus cells. During the pre-ovulat ory period, mural granulosa cells promote selective degradation of perifoll icular matrix, resulting in the formation of a follicle rupture site. Conve rsely, cumulus cells synthesize a large amount of a muco-elastic matrix tha t plays an essential role in the extrusion of the oocyte from the follicle and in the subsequent fertilization process. Formation of such matrix by cu mulus cells in the pre-ovulatory follicle appears to be controlled by a par acrine influence by the oocyte. We have shown that mouse oocytes modulate t he response of cumulus cells to an ovulatory gonadotropin stimulus by promo ting the synthesis and preventing the degradation of cumulus matrix. Theref ore, although gonadotropins are essential for triggering the complex events involved in ovulation, the oocyte appears to have an active role in this p rocess. In the present review current data and hypotheses concerning molecu lar mechanisms involved in the organization and synthesis of cumulus matrix are discussed.