Identification of TSSK1 and TSSK2 as Novel Targets for Male Contraception

The testis-specific serine kinases (TSSKs) are post-meiotically expressed in testicular germ cells. Their testis-specific expression, together with their putative role in phosphorylation pathways, suggests that TSSKs have relevant roles in spermiogenesis, sperm function, or both. Independent Tssk3 and Tssk6 knockout mice, as well as the double Tssk1/Tssk2 KO males, are sterile. However, the double KO results are silent regarding the individual roles of TSSK1 and TSSK2. The aim of this study was to develop independent mutant mouse models of Tssk1 and Tssk2, using CRISPR/Cas9, to evaluate their independent roles in reproduction. Male heterozygous pups were used to establish one Tssk1 and two independent Tssk2 mutant lines. Natural mating mutant Tssk1 and Tssk2 homozygous males but not females were found to be sterile. Additionally, homozygous males have lower sperm numbers and decreased motility, and were infertile in vitro. Anti-TSSK2 antibodies were validated against Tssk2 mutants and used in Western blot and immunofluorescence experiments. TSSK2 is localized to the sperm head; importantly, it is present in the testes and sperm from Tssk1 mutant mice, confirming individual mutation. Our results indicate that both TSSK1 and TSSK2 are individually essential for male reproduction and support both kinases as suitable nonhormonal male contraceptive targets.