Structure and function of the human oocyte-cumulus-corona cell complex before and after ovulation

The fine structure of the human cumulus oophorus has been reviewed on the b asis of scanning and transmission electron microscopic observations as well as of immunofluorescence data. Tissues sampled from preovulatory ovarian f ollicles and cumulus-enclosed oocytes and fertilized eggs (collected from t he oviduct or obtained during in vitro fertilization procedures) have been evaluated from a microtopographic and morphodynamic point of view in order to better clarify the possible role of this population of cells. In particu lar, the following aspects have been studied and discussed: the presence of multiple close contacts (modulated by the interposition of the zona pelluc ida) between the oocyte surface and the long microvillous evaginations proj ecting from the inner aspect of corona cells surface (through these structu res the intraovarian cumulus oophorus may control oocyte growth and metabol ism up until the time of ovulation); the occurrence of different subpopulat ions of cells (steroid-synthetic cells, cells producing adhesive proteins, leukocytes, macrophages) in the postovulatory, extraovarian cumulus oophoru s surrounding oocytes, zygotes and early developing embryos. All these elem ents found in the cumulus mass may positively act, through their paracrine activities, on the chemical composition of the microenvironment in which fe rtilization occurs.