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In Podarcis, undifferentiated, pre-differentiated and differentiated follicle cells can be recognised by shape, size, position and function. Undifferentiated (stromal) and pre-differentiated (small) cells are stem cells destined to proliferate and differentiate while differentiated cells (pyriforms) are nurse cells programmed to sustain oocyte growth and then degenerate at the end of previtellogenesis. The present work clarifies whether competence to undergo apoptosis in pyriforms is acquired at the time they originate from the small cells or later during aging. For this purpose the expression of Fas, Fas-L, caspase 3 and DNase I have been investigated by immunocytochemistry in small and pyriform cells. Results indicate that all these cell death factors are present exclusively in pyriforms. Their synthesis starts as soon as cells differentiate and that while aging, Fas and Fas-L are down and up regulated respectively. We conclude that pyriforms are committed for apoptosis since differentiation and that death occurs via mechanisms alternative to receptor or mitochondrial mediated pathways.

Using alpha and beta spectrin mammalian antibodies on Western blotting, we demonstrated that lizard ovarian follicles contain two isoforms of alpha spectrin, Mr 94 and 134 kDa, and a 230 kDa beta spectrin, and that their pattern modifies in relation to pyriform cell differentiation. In fact, a positive immunoreaction is firstly evident within follicular epithelium of previtellogenic follicles when small cells differentiate into pyriform cells via intermediate cells. Later on, immunostain is present in pyriform cells and in the oocyte cortex that previously appears unstained. It is noteworthy that immunostain is also present on small cells located in contact with the oocyte membrane, but not on those located under the basal lamina and among pyriform cells, not engaged in pyriform cell differentiation. During the subsequent stages of previtellogenic phase, spectrin immunostain over the follicular epithelium and in the oocyte cortex does not change. By contrast, in vitellogenic follicles, when the follicular epithelium is constituted only by small cells, immunostain is evident at the level of the oocyte cortex and the cytoplasm of regressing pyriform cells. The present data strongly suggest that the alpha and beta spectrin pattern put in evidence during the different phases of lizard oocyte growth is related to the differentiation of small into pyriform cells, where such protein may guarantee a relationship between surface glycoproteins (Andreuccetti et al., 2001: Anat Rec 263:1-9), and the cytoskeleton distribution (Maurizii et al., 2000: Raf Mol Reprod Dev 57:159-166). Furthermore, the distribution of spectrin mRNA, similar to that observed for the protein, demonstrates that spectrin, once synthesized within pyriform cells, is transferred through intercellular bridges in the oocyte cortex, thus confirming that pyriform cells are nurse that significantly are involved in the oocyte growth. Finally, the present data demonstrate that alpha spectrin of lizard ovarian follicles has Mr quite different from those so far reported and may constitute a new group of isoforms. This important result will be the focus of future experiments. Mol. Reprod. Dev. 67: 101-107, 2004.