REGULAR ARTICLE Block of mitochondrial apoptotic pathways in lizard ovarian follicle cells as an adaptation to their nurse function Stefania Tammaro & Palma Simoniello & Silvana Filosa & Chiara Maria Motta Received: 28 November 2005 / Accepted: 23 May 2006 / Published online: 12 October 2006 # Springer-Verlag 2006 Abstract Pyriforms are ovarian follicle nurse cells that undergo apoptosis at the end of previtellogenesis and are completely eliminated by the epithelium. This event is accompanied by the active transfer of organelles and macromolecules to the oocyte via an intercellular bridge. Since it would be a nonsense for damaged mitochondria to reach the oocyte, we have postulated that pyriform cells have adapted their apoptotic machinery to prevent mito- chondrial degradation. To verify this hypothesis, we have studied mitochondrial morphology and functionality during follicle cell regression. Cytological and biochemical evi- dence indicates that mitochondria in pyriforms maintain their size, organization and membrane potential. This clearly indicates that they are not involved in apoptosis signalling/progression. This block would favour both the oocyte, by increasing the pool of organelles available from follicle cells, and also the regressing pyriforms, by main- taining the energy resources required for completion of their nurse function. The block is probably attributable to an over-expression of Bcl-2 and might be carried out by sequestering cytochrome c inside the organelles. As demonstrated by in vitro experiments, the mitochondrial apoptosis pathway can be activated by stress induction, such as serum deprivation, but not following physiological pro-apoptotic signalling, such as treatment with gonadotro- phin-releasing hormone. Keywords Cell death . Mitochondrial morphology . Mitochondrial membrane potential . Gonadotrophin-releasing hormone . Bcl-2 . Lizard, Podarcis sicula (Lacertilia) Introduction In lacertids, the follicular epithelium markedly changes during previtellogenesis (Filosa 1973). Initially composed only by small stem cells, it later becomes polymorphic because of the differentiation of large pyriforms (P cells; Filosa et al. 1979). These are nurse cells that significantly contribute to maintenance of oocyte stock reserves by sending organelles such as vesicles, Golgi, ribosomal bodies, mitochondria (Taddei 1972; Motta et al. 1995) and messenger and ribosomal RNAs (Motta et al. 1995) to the oocyte via intercellular bridges (Andreuccetti et al. 1978). At the end of previtellogenesis, the epithelium undergoes remodelling and all the pyriforms regress via apoptosis as demonstrated by the appearance of typical cellular alterations: loss of contact, membrane blebbing, vesicle dilation, chro- matin margination, condensation and fragmentation (Motta et al. 1996). The process ends with the formation of apoptotic bodies: these are either engulfed by the adjacent small cells (S cells; Motta et al. 1996) or recycled by the oocyte, as suggested by the presence of internucleosomal DNA in yolk vesicles (Motta et al. 2001). Regression of all pyriforms is completed by the time vitellogenesis begins, so that, until ovulation, the epithelium remains composed exclusively of a single layer of S cells (Filosa 1973). As demonstrated morphologically, pyriforms do not stop their transfer of materials to oocytes during apoptosis. Indeed, the intercellular bridges become engulfed with organelles, in particular, mitochondria (Motta et al. 1996). Cell Tissue Res (2007) 327:625–635 DOI 10.1007/s00441-006-0256-7 These studies were supported by a grant from the MIUR (PRIN project: Molecular responses of embryonic, differentiated and tumoral cells exposed to cadmium intoxication). S. Tammaro : P. Simoniello : S. Filosa : C. M. Motta (*) Dipartimento delle Scienze Biologiche, Section of Evolutionary and Comparative Biology, University of Naples Federico II, 80134 Naples, Italy e-mail: chiaramaria.motta@unina.it