The Role of the Oocyte in Ovulation

Abstract

Ovulation requires 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. In most mammals, prior to ovulation, mural granulosa cells promote selective degradation of perifollicular matrix, resulting in the formation of a thinner area at the follicular apex. At the same time, the cumulus cells synthesize and deposit a large and viscoelastic extracellular matrix around the oocyte, a process known as cumulus expansion or mucification. As ovulation approaches, the apical follicle wall breaks, and a hole is formed that is sufficiently large to allow a portion of the cumulus mass to pass through it. Deformation of the cumulus matrix allows the passage of the first cumulus cells through the rupture site, after which the oocyte, surrounded by the remaining cumulus cells, is rapidly extruded from the follicle. Cumulus cells and the oocyte remain firmly bound within the matrix so that they are not dispersed during the extrusion.