Changes in expression and localization of X-linked inhibitor of apoptosis protein (XIAP) in follicular granulosa cells during atresia in porcine ovaries.

Follicular selection predominantly depends on granulosa cell apoptosis in porcine ovaries, but the molecular mechanisms regulating the induction of apoptosis in granulosa cells during follicular selection remain incompletely understood. To determine the role of X-linked inhibitor of apoptosis protein (XIAP), which suppresses caspase-3, -7 and -9 activities and acts as an endogenous inhibitor of apoptotic cell death, in the regulation of granulosa cell apoptosis during follicular atresia, we examined the changes in the expression level and localization of XIAP mRNA and protein in granulosa cells during follicular atresia using reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, Western blotting and immunohistochemistry, respectively. High levels of XIAP mRNA and protein were noted in the granulosa cells of healthy follicles, and decreased levels were noted during follicular atresia. In situ hybridization and immunohistochemistry demonstrated that XIAP mRNA and protein were strongly expressed in the granulosa cells of healthy follicles, but negative/trace stainings were noted in those of atretic follicles. The present findings strongly indicate that XIAP is a candidate molecule which acts as an anti-apoptotic/pro-survival factor by inhibiting intracellular apoptosis signaling and is involved in the regulation of apoptosis in porcine granulosa cells.