Antral follicle development influences plasma membrane organization but not cortical granule distribution in mouse oocytes

In the present study, we evaluated the contributions of antral follicle dev elopment and antral granulosa cell-released factor(s) to the acquisition of a mature mouse oocyte plasma membrane organization and cortical granule di stribution. This has been performed by comparing in-vitro matured oocytes d erived from early antral follicles (here referred to as denuded oocytes) or from pre-ovulatory follicles,and cultured either as cumulus-intact or cumu lus-free oocytes, with in-vivo ovulated eggs. By using scanning and transmi ssion, electron microscopy, the denuded oocyte surface appears to be charac terized by the presence of long microvilli, while that of pre-ovulatory ooc ytes and of ovulated eggs by shorter microvilli. However, denuded oocytes c an acquire a pre-ovulatory-like plasma membrane configuration when matured in vitro in the presence of early antral granulosa or cumulus cells, but no t of NIH-3T3 fibroblasts. On the country, fluorescence and confocal microsc opy analyses after labelling with fluorescent Lens culinaris agglutinin sho w that all the oocyte classes analysed are characterized by similar cortica l granule distribution and density. Thus, complete antral follicle developm ent plays an important role in the process of oocyte surface differentiatio n, probably through the action of antral granulosa cell-released factor(s), but it does not affect oocyte capacity to normally distribute cortical gra nules.