Sperm associated antigen 8 (SPAG8), a novel regulator of activator of CREM in testis during spermatogenesis.

cAMP response element modulator (CREM)-mediated gene expression is an essential regulatory mechanism for germ cell differentiation. CREM and its coactivator in testis, ACT, activate the transcription of many essential genes for spermatogenesis. Sperm associated antigen 8 (SPAG8) is a testis-specific component that is expressed during germ cell differentiation. In this study, we found the pattern of SPAG8 expression largely overlapped with that of ACT during spermatogenesis and verified the association of SPAG8 with ACT. Furthermore, we showed that SPAG8 enhanced the transcriptional activation of ACT-mediated CREMτ by strengthening the binding of ACT to CREMτ. These results indicate that SPAG8 acts as a regulator of ACT and plays an important role in CREM-ACT-mediated gene transcription during spermatogenesis.