Sperm Associated Antigen 4 (SPAG4)

Mammalian sperm tails contain, besides an axoneme, 2 unique components: outer dense fibers (ODF), which extend along the entire tail, and a fibrous sheath (FS), which initiates at the stack of mitochondria and surrounds the ODF until the end of the sperm tail. SPAG4 associates with an outer dense fiber protein via a leucine zipper motif and localizes to the microtubules of the manchette and axoneme during sperm tail development.One of the novel genes encoded the major 84-kD ODF protein , the human homolog of which maps to 9q34. Another of the new genes, SPAG4, also encoded a product that interacted strongly with ODF27 via a leucine zipper and was expressed exclusively, although transiently, in elongating spermatids; protein synthesis of SPAG4 was maximal during maximal ODF27 synthesis and growth of the sperm tail.