SPATA12, also known as SRG5 (Spermatogenesis-related protein 5), is a 190 amino acid protein that may be involved in the regulation of spermatogenesis. SPATA12 is expressed in normal adult testis, but is absent in fetal testis, implying that it may be involved in the development of testicular maturation. Specifically, SPATA12 is expressed in spermatocytes, spermatids and spermatozoa, with no expression in Leydig and Sertoli cells. Studies with HeLa and GC-1 germ cells indicate that expression of the SPATA12 gene may delay the progression of G1 to S in the cell cycle, therefore it is thought that SPATA12 maintains the cell in a differentiated state and suppresses cell proliferation.