Spata17?gene, which called MSRG11, by digital differential display of ESTs found only in testis. The deduced 292-amino acid protein was considered to be a member of the family of calmodulin (CaM)-binding proteins because it contained 3 short CaM-binding motifs containing conserved ile and gln residues (IQ motif). Spata17 protein was most abundant in the cytoplasm of round spermatids and elongating spermatids within seminiferous tubules of the adult testis. Expression gradually decreased in the manipulated testis of animals that underwent experimental unilateral cryptorchidism. Transient transfection experiments with a Spata17 expression construct in cultured spermatogonia GC-1 cells indicated that Spata17 accelerated apoptosis in a dose-dependent manner.