Immunolocalization of cytoskeletal proteins in the previtellogenic ovarian follicle of the lizard Podarcis sicula

Abstract

We report the immunolocalization of intermediate filament proteins (vimentin and cytokeratins) in the previtellogenic ovarian follicle of the lizard Podarcis sicula. Vimentin is present, in accordance with their mesenchymal origin, in all the cells of the polymorphic follicular epithelium (small, intermediate and pyriform). Cytokeratin, absent from the small follicle cells, is present in those cells (intermediate and pyriform) connected to the oocyte by an intercellular bridge. In particular, this protein surrounds the nucleus in the pyriform cells and is mainly localized at the apex adjacent to the oocyte surface; it forms a network, that crosses the zona pellucida through the intercellular bridge and appears to be continuous with a cortical ring of cytokeratin in the oocyte. The presence of a cytokeratin cytoskeleton in the pyriform cells in continuity with that of the oocyte lends support to the previously reported hypothesis that, during oogenesis in Podarcis sicula, somatic cells constitute an integral system with the germ cell and provide for its growth. Preliminary observations indicating the presence of actin and tubulin inside the cytoplasmic bridges connecting the pyriform cells to the oocyte are in agreement with an involvement of these connections in the transfer of cytoplasmic materials.