AJ-p97: a novel antigen of the human sperm tail fibrous sheath detected by a neurofilament monoclonal antibody.

Using indirect immunofluorescence (IIF), the RT97 anti-neurofilament monoclonal antibody (MoAb) detected an intracellular antigen in the principal piece of human ejaculated sperm tails. Its localisation to the tail fibrous sheath (FS) was confirmed by immunoelectron microscopy (IEM), which showed the binding of the gold particles to the outer FS surface. During spermatogenesis the antigen was first expressed on the spermatid FS, and its expression was continued on ejaculated mature sperm. In Western blotting of sperm lysates, the RT97 reacted with a 97 kDa protein (AJ-p97) which lacked disulphide bonds. This antigen was not detected on mouse or rat sperm tail FS, suggesting a sequence divergence of the AJ-p97 during evolution. The significance of these results and the relationship of AJ-p97 to neurofilaments are discussed, together with the use of the antibody as a probe for the structural dissection of the FS and for analysing the molecular events that take place during spermiogenesis, especially those involved in sperm tail morphogenesis.