HETEROGENEOUS DISTRIBUTION OF FIBRONECTIN TENASCIN-C, AND LAMININ IMMUNOREACTIVE MATERIAL IN THE CUMULUS-CORONA CELLS SURROUNDING MATURE HUMAN OOCYTES FROM IVF-ET PROTOCOLS - EVIDENCE THAT THEY ARE COMPOSED OFDIFFERENT SUBPOPULATIONS - AN IMMUNOHISTOCHEMICAL STUDY USING SCANNING CONFOCAL LASER AND FLUORESCENCE MICROSCOPY

Monoclonal antibodies and immunofluorescence microscopy, including las er confocal microscopy, were used in this study to point out the produ ction of fibronectin, tenascin-c, and laminin in the cumuluscorona (CC ) cells surrounding mature human oocytes from IVF-ET protocols in view of their presumptive importance in the coordination of the processes leading to fertilization and early embryo cleavage, including the fina l maturation of the ovum, the sperm-egg interaction, and the ''complex biochemical dialogue'' between the gamete and the oviduct through the tubal luminal environment. One hundred fifty mature oocyte-CC complex es were obtained from IVF-ET protocols and fixed in 4.0% buffered para formaldehyde. Specimens were incubated with a panel of primary monoclo nal antibodies (mabs) recognizing different epitopes of fibronectin, t enascin-c, and laminin and then with fluorescein isothiocyanate-conjug ated goat anti-mouse IgG. Observations were made by a scanning confoca l microscope (Sarastro 2000) and a photomicroscope (Polyvar, Reichert= lung) equipped with epifluorescence optics. The immunohistochemical da ta demonstrated that human CC cells are capable of producing fibronect in and tenascin-c but that their production is not homogeneous in the CC population. In fact, fibronectin immunoreactivity was shown mostly by inner CC cells (mainly corona cells), whereas tenascin was produced by some cells scattered in the entire cumulus mass. Moreover, fibrone ctin and tenascin-c immunoreactive material was observed in the intrac ytoplasmic areas, at the plasma membrane level as well as in the extra cellular matrix. On the contrary, laminin immunofluorescent material w as found around plasma membranes of almost all CC cells, but a clear i ntracytoplasmic reaction was never observed. This leads us to assume t hat laminin in the extracellular matrix remains entrapped once produce d by granulosa follicular cells and that in the postovulatory period n o active secretion occurs in CC cells. Even though the functional role of these extracellular matrix proteins remains still unclear, it is r easonable to suggest that they are necessary in various steps of the r eproductive process, i.e., from the pick-up of the oocyte, its transpo rt through the oviduct, and fertilization, up until the early cleavage of the embryo. Finally, functional differences between ''corona radia ta'' and ''cumulus'' cells during the oocyte denudation may be account ed for particular distribution of these adhesive proteins. (C) 1996 Wi ley-Liss, Inc.