Block of mitochondrial apoptotic pathways in lizard ovarian follicle cells as an adaptation to their nurse function

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 mitochondrial degradation. To verify this hypothesis, we have studied mitochondrial morphology and functionality during follicle cell regression. Cytological and biochemical evidence 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 maintaining 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 gonadotrophin-releasing hormone.

Ovarian Oxidative Stress Induced Follicle Depletion After Zona Pellucida 3 Vaccination Is Associated With Subfertility in BALB/c Mice

“…As expected, ROS accumulation in ovarian cells and whole tissues reached high levels, while MDA and T-AOC levels were increased and decreased, respectively, suggesting a serious OS and potential mitochondrial dysfunction in ovarian cells of ZP3-immunized mice, and the resulting side effects maybe also associated with the inflammation in the AOD model (11,18,19). Moreover, there are conclusive evidence has demonstrated that mitochondrial OS is a key activator of apoptosis-induced follicles depletion (47)(48)(49)(50). Therefore, evaluation of caspase, antiapoptotic and pro-apoptotic protein levels was further examined and it appeared that mitochondrial apoptotic pathway was involved in the progression of AOD, with apoptosis-induced follicular damage found to directly cause ovarian inflammationassociated reduction of follicle number.…”

Comparative expression analysis in mature gonads, liver and brain of turbot (Scophthalmus maximus) by cDNA-AFLPS

“…α spectrine is required for germ line cell division and differentiation in the Drosophila ovary. Notothenoids have an unusual abundance of spectrine suggesting that the various isoforms present may carry out different functions during oocyte maduration (Tammaro et al, 2007) Pax5 encodes a member of the paired box family of transcription factors. This gene encodes the B-cell lineage specific activator protein and also its expression has been detected in developing central nervous system and testis and so may play a role in neural development and spermatogenesis (Adams et al, 1992).…”

cGnRH II involvement in pyriform cell apoptosis

“…Apoptosis would end with the formation of a few apoptotic bodies that would be phagocytosed by the small cells (Motta et al 1996) or, alternatively, transferred into the oocyte and packed with the yolk as suggested by the presence of internucleosomal DNA in yolk globlets . The existence of an alternative apoptosis route in LP pyriforms is supported by evidence that, in these cells, the mitochondrial pathway is also physiologically inhibited, as LP pyriforms over-express the mitochondrial anti-apoptotic factor bcl-2 (Tammaro et al 2007). …”