Probably plays a regulatory role in sperm development. May participate in regulation of fibrous sheath (FS) assembly by supporting the formation of disulfide bonds during sperm tail morphogenesis. May also be required to rectify incorrect disulfide pairing and generate suitable pairs between the FS constituents. Can reduce disulfide bonds in vitro in the presence of NADP and thioredoxin reductase (By similarity). Testis-specific. Strongly expressed in the testicular seminiferous tubules, mostly in the round spermatids. Transiently expressed in spermiogenesis, being mostly concentrated in the periaxonemal compartment of the tail of the elongating spermatid, where it transiently associates with the longitudinal column of the FS. In the very last steps (steps 17-19), when periaxonemal expression disappears, it is still weakly present in the shrinking cytoplasmic lobe (at protein level).