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 peptide associates with the fibrous sheath in mature spermatozoa and localizes to the principal piece of sperm tail, while the 55-kDa peptide localizes to the midpiece. Detected in the cytoplasm of almost all spermatogonial cells within the seminiferous tubules (By similarity). Processed into N-terminal 27-kDa and C-terminal 55-kDa fragments. Belongs to the CEP135/TSGA10 family.