Calcium-binding protein (PubMed:19271754). Essential for maintaining the structural integrity of the sperm flagella (By similarity). Mostly cytoplasmic, but associated with the mitochondrial inner membrane during the last steps of spermatid differentiation (PubMed:19271754). Localizes to the principal piece of the sperm flagellum (By similarity). Expressed in seminiferous tubules of the testis in step 10 spermatids (stage X), subsequently increasing to reach maximal levels of step 18 elongated spermatids (stage VI) (at protein level). Strongly expressed in testis. Weakly expressed in olfactory epithelium. Expressed in spermatids of seminiferous tubules at steps 4-14 (stages IV to XIV of the seminiferous epithelium classification). Truncated N-terminus.