Identification of a Protein in the Fibrous Sheath of the Sperm Flagellum1

The fibrous sheath is a unique cytoskeletal component in the principal-piece segment of the mammalian sperm flagellum. Monoclonal antibody ATC was shown by indirect immunofluorescence (IIF) to bind to the principal piece of the flagellum of permeabilized mouse, rat, and hamster sperm, but not to that region of guinea pig, rabbit, or human sperm. IIF on isolated fibrous sheaths confirmed that the antigen was present in the fibrous sheath of mouse, rat, and hamster sperm. On Western blots of mouse spermatozoa, ATC identified a relatively insoluble major antigen with an apparent molecular weight of 67,000 (Mr67,000). Hamster sperm fibrous sheaths contain an antigen of Mr66,000, while rat sperm fibrous sheaths contain an antigen of Mr65,500. The antigen was first detected in late spermatids, as determined by immunohistochemical procedures on sections of mouse, rat, and hamster testis. The antigen was not detected on Western blots of mouse brain, kidney, liver, or thymus. These results indicate that ATC recognizes a protein integral to the fibrous sheath of the principal piece of sperm detected by immunohistochemistry late in spermiogenesis that is probably restricted to the male germ cell line.