The Role of autophagy during spermatogenesis in mice

Spermatogensis is a complex and highly regulated process to produce haploid mature sperm. During final step of spermatogenesis, known as spermiogenesis, sperm eliminate most of the cytoplasm to facilitate sperm motility. It is generally believed that most of which is degraded by the Sertoli cells. However, it remains unknown about how the large mass of discarded cytoplasm and orgenelles (residual bodies) are rapidly degraded. Autophagy is primary process for degradation of cytoplasmic contents, including proteins and organelles, in the lysosome. When autophagy is induced, double membrane structure appeared, enclosed the portion of cytoplasm, including proteins and organelle, and fused to lysosome resulting in the generation of autolysosome. Using GFP-LC3 mice, which are autophagy monitor mice, we found that autophagy is induced during spermiogenesis. Electron microscopic analysis also revealed that autophagosome-like structures appeared in sperm cytoplasm. Since autophagy is bulk degradation system, we hypothesized that autophagy could be involved in the sperm cytoplasm elimination. To examine this possibility, we generated sperm-specific conditional Atg5 knockout mice and found that these knockout males are infertile around 15 weeks. Histochemical analysis of knockout testis sections revealed that abnormal structures accumulated within seminiferous tubules. Electron microscopic analysis showed that these abnormal structures contained multiple sperm cytoplasmic components. Due to accumulation of abnormal structures, morphologically abnormal sperm and large amount of debris were obtained from cauda epididymis in autophagy knockout testis. Western blot analysis revealed that germ-cell proteins still present in the autophagy-knockout sperm, indicating the impairment of sperm cytoplasmic elimination. Thus, our results suggest that autophagy could be essential for proper cytoplasm remodeling during spermiogenesis in mice. (Supported by a Grant-in-Aid for Young Scientist (A) from MEXT, Japan)The 7th Annual meeting of ARB