Abstract
Testes of the sea urchin, Strongylocentrotus purpuratus, undergo morphological changes consistent with a reproductive season that includes the winter months in the northern hemisphere (c. November to March). These changes can be observed in the basal germinal epithelia (BGE) of testicular acini as alterations in the gradients of meiosis and spermatogenesis from the peripheral (basal) to the inner (luminal) regions. Early in the season, large numbers of spermatogonia and primary spermatocytes along with large, spherical nutritive phagocytes (NPs) occupy most of the BGE. Relatively few secondary spermatocytes, spermatids, and spermatozoa are present. In the middle of the season more spermatocytes, spermatids, and spermatozoa are observed within well-defined spermatogenic columns that run between elongated NPs. Late in the season the BGE diminishes as the number of spermatogenic cells within it decreases dramatically and the lumen becomes distended with mature spermatozoa. To trace the origin and location of a 210 KD sperm surface antigen during spermatogenesis, a monoclonal antibody that recognizes this antigen, MAb J18/2, was used to probe testis sections. Indirect immunofluorescence microscopy detected the antigen throughout the BGE. Immunogold electron microscopy further localized it to the intracellular vesicles within spermatogenic cells of all stages. In mature spermatozoa the 210 KD surface antigen was detected not only on the sperm surfaces overlying the acrosomes and tails but also within the acrosome, suggesting the presence of an intracellular store of this antigen. Other than the occasional detection of antigen within the residual bodies of NPs, which contain phagocytosed spermatozoa, no antigen was detected in somatic cells of the testis, indicating that it is generated within the spermatogenic cells themselves.