FNDC3A is a 1,134 amino acid protein that belongs to the FNDC3 family of proteins. FNDC3A contains an N-terminal proline-rich region, nine fibronectin type-III domains (none of which contain an RGD sequence) and a hydrophobic C-terminal transmembranous helix. Expressed in a wide variety of tissues, FNDC3A localizes to Golgi vesicles and to the developing acrosome of spermatids. FNDC3A is believed to function in glycosaminoglycan and collagen synthesis. In mice, a mutation in the gene encoding FNDC3A causes male sterility due to defective adhesion between Sertoli cells and spermatids in the seminiferous epithelium. This suggests that FNDC3A plays an important role in spermatogenesis, possibly mediating or maintaining the adhesion between Sertoli cells and spermatids.