VITELLINE ENVELOPE FORMATION DURING OOGENESIS IN BUFO-ARENARUM

The formation of vitelline envelope (VE) during the oogenesis of Bufo arenarum (Amphibia Anura) is described. At the stage of early vitellog enesis, the first structures appear: the number of oocyte microvilli i ncreases, and many cross sections of them are observed between the fol licle cells and the oocyte. A filamentous material is observed inside the follicle cells and between the follicle cells and the oocyte. Mult ivesicular bodies are also found in the follicle cells, and in the per ivitelline space. The micrographs also suggest the participation of th e oocyte in the process of VE formation: large vesicles are present in the cortex of the oocyte, filled with an amorphous material of low an d uniform electron density. Some of them are in the process of releasi ng their content to the perivitelline space. Many vesicles (probably r esulting from microvilli fragmentation) are also observed in the periv itelline space. During late vitellogenesis the VE is a continuous stru cture between the layer of follicle cells and the oocyte. The filament ous material is aggregated in bundles, forming a net, and the spherica l components are now either included in the orifices of the net, or fr ee near the oocyte's surface. At the end of oogenesis, when the VE is completely formed, it is difficult to distinguish its components indep endently. Immunolocalization with antibodies against VE, show a positi ve reaction in follicle cells and oocytes in previtellogenic and full grown ovarian follicles. This analysis suggests that both the oocyte a nd the follicle cells are directly involved in the synthesis and secre tion of the components of the vitelline envelope in Bufo arenarum.