Expressional and functional analyses of epididymal SPINKs in mice.

Epididymal maturation is critical for acquisition of motility and fertilizing capacity by sperm. During epididymal transit, the surface of sperm undergoes prominent sequential changes through interactions with secreted proteins, including protease inhibitors. In the present study, we characterized three epididymis-specific SPINKs (serine protease inhibitors, Kazal-type): SPINK8, SPINK11, and SPINK12. We found that these epididymal SPINKs are expressed in an epididymal region-specific manner and their expression is developmentally regulated. Remarkably, cellular analyses revealed that SPINK8 and SPINK12 are transferred to the sperm. To investigate the in vivo properties of SPINK12, we analyzed knockout mice generated by CRISPR/Cas9-mediated genome editing. Loss of SPINK12 did not alter epididymal tubule structure or sperm phenotypes. Spink12 mutant mice exhibited normal fertility, suggesting that SPINK12 is functionally redundant in the epididymis.