Follicle cell differentiation in the wall lizard Podarcis sicula

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.