The acrosomal protein SP-10 (Acrv1) is an ideal marker for staging of the cycle of seminiferous epithelium in the mouse.

The study of spermatogenesis in the mouse requires accurate identification of the cycle stage of seminiferous epithelium. A stage refers to the unique association of germ-cell types at a particular phase of development, as seen in a testicular cross section. The process of staging, however, is a daunting task. There are 12 stages represented in the mouse seminiferous tubule. Stages are typically identified on the basis of the morphology of the developing acrosome of spermatids. Although the characteristic features of the acrosome are well-documented in ultrastructure images, a reagent that can highlight the subtle differences in acrosome shape under the light microscope is lacking. Here we demonstrate that a polyclonal antibody raised against the mouse acrosomal protein SP-10 is extremely useful for stage identification. Immunohistochemistry showed that the anti-SP-10 antibody is highly specific for the acrosome of spermatids, as no other cell type in the epithelium showed immunoreactivity. At lower magnification, the gross shape of the acrosome and the increasing intensity of immunostaining served as a guide for the identification of stages 1–12. At higher magnification, characteristic morphological features –such as whether the part of the acrosome that contacts the nuclear surface is round (stage 3) or flat (stage 4) or curved (stage 6)– could be identified unambiguously. Overall, we present evidence that SP-10 is a useful marker for staging the cycle of a seminiferous epithelium. The anti-SP-10 antibody works well in different fixatives, on paraffin-embedded as well as cryosections; it has also been shown to be useful for characterizing spermatogenic defects in mutant mice.