Plays a role in spermatogenesis (By similarity). When overexpressed, prevents nuclear localization of HIF1A (By similarity). Interacts with HIF1A. In mature spermatozoa, localizes to the centriole and midpiece (By similarity). The 27-kDa N-terminal fragment associates with the fibrous sheath in mature spermatozoa and localizes to the principal piece of sperm tail, while the 55-kDa fragment localizes to the midpiece (PubMed:14585816). Detected in the cytoplasm of almost all spermatogonial cells within the seminiferous tubules (PubMed:16643851). Expressed in testis, predominantly in elongated spermatids (at protein level) (PubMed:14585816, PubMed:16643851). Detected in spermatocytes only at the mRNA, but not at the protein level (PubMed:14585816). Becomes detectable in testis between postnatal days 15 and 21 and expression levels remain high in the adult. Not detected in fetal testis. Processed into N-terminal 27-kDa and C-terminal 55-kDa fragments. Belongs to the CEP135/TSGA10 family.