TSKS and male infertility: Human TSSKs did not rescue male infertility of dTSSK−/− flies; therefore, we wondered whether the N-terminal (1–26 aa) and C-terminal (292–302 aa) domains of dTSSK, which are poorly conserved with human TSSKs (Figs. S1a and S2a), are critical for spermiogenesis in Drosophila. We generated transgenic flies expressing dTSSKΔN (deleted N-terminal 26 aa) and dTSSKΔC (deleted C-terminal 11 aa).