Testis-specific serine kinase substrate (TSKS) was identified as a substrate for testis-specific serine kinase 1 (TSSK1) and TSSK2. Although these three proteins co-localize to nuage, double knockout (KO) mice lacking TSSK1 and TSSK2 (Tssk1/2 dKO mice) exhibit abnormal mitochondrial sheath formation, suggesting that these proteins and nuage are involved in mitochondrial sheath formation. However, the previous study observed abundant cytoplasm in the late spermatids at seminiferous tubule stage VIII of the Tssk1/2 dKO mouse. Furthermore, an interaction between TSKS and phosphatase protein PPP1CC2 was also reported previously. Protein phosphatase 1 catalytic subunit gamma (Ppp1cc) is a member of the PP1 family of protein phosphatases that encodes two splice isoforms: the ubiquitous Ppp1cc1 and the testis-specific Ppp1cc2. Ppp1cc knockout (KO) male mice also exhibit malformed mitochondrial sheath formation. These data indicate that the kinase and phosphatase of TSKS are involved in the formation of the mitochondrial sheath (PMID: 36881620).