Oviductal sperm storage in the Chinese pond turtle, Mauremys reevesii , depends on androgen-based promotion of the BCL 2 anti-apoptotic pathway

Sperm storage is a complex and highly coordinated process that is regulated by a variety of factors. The BCL 2 protein family plays a key role in regulating apoptosis, and determines sperm survival. The objective of this study was to explore the correlation between sperm storage and the BCL 2 protein family in the oviduct of Mauremys reevesii . Hematoxylin-eosin (HE) staining, immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (RT-qPCR) techniques were used to investigate three parts of the reproductive tract (isthmus, uterus and vagina) of mated and unmated female M. reevesii . Hematoxylin-eosin staining revealed many sperm stored in the oviduct. IHC showed positive immunostaining for the BCL 2 and BAX proteins in epithelial ciliated and glandular cells. RT-qPCR indicated that the mRNA expressions of anti-apoptotic genes (BCL 2 , MCL 1 , BCL- W , BCL-XL ) and the androgen receptor (AR) were significantly higher in mated turtles than unmated turtles. However, the expression of pro-apoptotic genes (BAX , BAD , BID and CASPASE 3 ) showed the opposite relationship. These results suggest that sperm entering the oviduct can promote the synthesis of anti-apoptotic genes to protect themselves from various degradation factors. These findings will help researchers understand the mechanisms of sperm storage.