Fibronectin Type III Domain Containing Protein 3 (FNDC3)

Fndc3a is a member of a three-gene family in mice. Fndc3a, which is expressed in several tissues including testis, encodes a novel protein composed of a proline-rich amino-terminus, nine fibronectin type-III domains, and a hydrophobic carboxy-terminus. Immunohistochemical staining indicated that FNDC3A localizes to the acrosome of spermatids, as well as to Leydig cells in the mouse testis. Acrosomal localization of FNDC3A is observed in spermatids between step 2 and step 10 inclusive. In step 12 spermatids, FNDC3A is largely absent from the acrosomal region with immunostaining being localized to vesicular structures located within the cytoplasm of elongate spermatids. Models are presented for the function of FNDC3A in mediating spermatid-Sertoli adhesion during mouse spermatogenesis.