No abstract

In this work we carried out an ultrastructural analysis of the cell interface between oocyte and follicle cells during the oogenesis of the amphibian Ceratophrys cranwelli, which revealed a complex cell-cell interaction. In the early previtellogenic follicles, the plasma membrane of the follicle cells lies in close contact with the plasma membrane of the oocyte, with no interface between them. In the mid-previtellogenic follicles the follicle cells became more active and their cytoplasm has vesicles containing granular material. Their apical surface projects cytoplasmic processes (macrovilli) that contact the oocyte, forming gap junctions. The oocyte surface begins to develop microvilli. At the interface both processes delimit lacunae containing granular material. The oocyte surface has endocytic vesicles that incorporate this material, forming cortical vesicles that are peripherally arranged. In the late previtellogenic follicle the interface contains fibrillar material from which the vitelline envelope will originate. During the vitellogenic period, there is an increase in the number and length of the micro- and macrovilli, which become regularly arranged inside fibrillar tunnels. At this time the oocyte surface exhibits deep crypts where the macrovilli enter, thus increasing the follicle cell-oocyte junctions. In addition, the oocyte displays coated pits and vesicles evidencing an intense endocytic activity. At the interface of the fully grown oocyte the fibrillar network of the vitelline envelope can be seen. The compact zone contains a fibrillar electron-dense material that fills the spaces previously occupied by the now-retracted microvilli. The macrovilli are still in contact with the surface of the oocyte, forming gap junctions.

The physiological significance of follicle cell-oocyte gap junctional coupling in the ovarian follicle Bufo arenarum was investigated. Lucifer Yellow injected into the oocyte readily passed to the overlying follicle cells, demonstrating effective dye coupling. We determined that the gap junction coupling varies during the annual sexual cycle. In winter there is a marked decrease in the amount or absence of heterologous gap junction contacts. In contrast, during the breeding season, gap junctions were normally coupled. We studied in vivo and in vitro the effects of frog pituitary hormone (FPH) and follicle stimulating hormone (FSH) on gap junction coupling. The results suggest that FSH induce the coupling of gap junctions enabling a greater metabolic cooperation necessary for oocyte growth and maintenance.On the other hand, nuclear maturation under physiological conditions seemed to have a direct consequence on the gap junction uncoupling and the interruption of the gap junctional flow of an oocyte maturation inhibiti 3n factor by the effects of LH-like gonadotropin or progesterone. 0 1996 Wiley-Liss, Inc.