Cytokeratin cytoskeleton in the differentiating ovarian follicle of the lizard Podarcis sicula Raf.

By immunoblotting and immunocytochemical techniques, we characterized the cytokeratins previously localized by us in the previtellogenic ovarian follicle of Podarcis sicula. Our results show that these cytokeratins correspond to those expressed in the monolayered epithelia. In fact, the immunoblotting analysis showed that the NCL-5D3 antibody, specific for human low molecular weight cytokeratins expressed in monolayered epithelia, reacted with the cytokeratins extracted both from the ovary and from the monolayered intestinal mucosa of Podarcis sicula. Furthermore, this antibody, in this reptile as in humans, clearly immunolabeled sections of corresponding tissues. The organization of the cytokeratin cytoskeleton in the main steps of the ovarian follicle differentiation was also clarified. The reported observations suggest that in Podarcis sicula, the cytokeratin cytoskeleton is absent in the early oocytes. It first appears in the growing oocytes as a thin cortical layer in concomitance with its becoming visible also in the enlarging follicle cells. In the larger follicles, this cytoskeleton appears well organized in intermediate cells and in particular in fully differentiated pyriform cells. In both these cells a cytokeratin network connects the cytoplasm to the oocyte cortex through intercellular bridges. At the end of the previtellogenic oocyte growth, the intense immunolabeling of the apex in the regressing pyriform cells suggests that the cytokeratin, as other cytoplasmic components, may be transferred from these follicle cells to the oocyte. At the end of the oocyte growth, in the larger vitellogenic oocytes surrounded by a monolayer of follicle cells, the cytokeratin constitutes a heavily immunolabeled cortical layer thicker than in the previous stages.