Sperm associated antigen 9 (SPAG9): a new member of c-Jun NH₂-terminal kinase (JNK) interacting protein exclusively expressed in testis

Abstract

Previously, we cloned and sequenced a novel human sperm associated antigen 9 (SPAG9). Northern blot analysis and RNA in situ hybridization experiments revealed testis- and stage-specific expression of SPAG9 mRNA, mainly confined to round spermatid suggesting haploid germ cell expression. Studies on the human and non-human primates (macaque and baboon) have shown a homology of 84.9% and 90.6% at amino acid level and 94% and 96.8% at DNA level, respectively. The presence of high level of homology at amino acid and DNA level indicates that SPAG9 is conserved in human, baboon and macaque sharing common function and common origin in the biological past. In addition, SPAG9 protein revealed structural homology with c-Jun NH₂-terminal kinase (JNK) interacting protein (JIP). The amino acid sequence analysis of SPAG9 predicted coiled coil, leucine zipper and transmembrane domain, speculating the involvement of SPAG9 mediated signal transduction pathways in reproductive processes.