Characterization of a cell-surface differentiation antigen of mouse spermatogenesis: timing and localization

The XT-1 antigen, bound by monoclonal antibody XT-I, is a differentiation antigen of germ cells in the mouse testis. As seen in immunoperoxidase-stained tissue sections from several juvenile ages and adult, the antigen becomes detectable on early (leptotene/zygotene) spermatocytes and increases in staining during spermatocyte development. During spermatid development the distribution of the determinant shifts from its relatively uniform surface distribution on spermatocytes to a more restricted localization on the base of the head, tail and cytoplasmic lobe of the elongating spermatid. The antigen is not detectable on juvenile or adult Sertoli cells. Detection of the antigen is dependent on the presence of germ cells of appropriate developmental stage. It is, thus, a marker for spermatocytes and later germ cells, for a cell-surface molecule related to spermatogenesis and for redistribution and/or modification of the molecule during spermatid elongation.