Characterization of a sperm-specific nuclear autoantigenic protein. II. Expression and localization in the testis

The testis- and sperm-specific nuclear autoantigenic protein, NASP, has a 2.5-kb mRNA that encodes a protein of molecular weight 73,533 and has several structural features of nuclear proteins. To further characterize NASP and confirm the structural predictions that NASP was a nuclear protein, specific immunostaining using a specific anti-recombinant protein antibody and in situ hybridization with a cDNA were used. In testis sections, NASP was first detected in the nuclear area of primary spermatocytes. During the subsequent meiotic divisions, NASP was partitioned into the cytoplasm and then reassociated with the reforming nucleus. No antibody labeling was associated with the chromatin. During spermiogenesis, NASP became restricted to the post-acrosomal region of the spermatozoon, although some labeling appeared in residual bodies and subsequently in the tubule lumen. NASP was not found in somatic cells. The detection of NASP mRNA transcripts in primary spermatocytes by in situ hybridization supported the immunolocalization results and indicated that NASP expression was under transcriptional control.