ANALYSIS OF THE PROTEIN-COMPOSITION OF THE MOUSE SPERM PERINUCLEAR THECA AND CHARACTERIZATION OF ITS MAJOR PROTEIN CONSTITUENT

The perinuclear theca (PT) is a cytoskeletal structure that covers the nucleus of mammalian spermatozoa and is believed to have a membrane-b inding role. The objectives of this study were to analyze the protein composition of the mouse PT, to identify and sequence its major protei n component, and to characterize this protein's transcriptional and tr anslational origins during spermatogenesis. The PT was extracted from demembranated and acrosome-depleted mouse sperm heads by alkaline trea tment. The protein profile of the PT extract was composed of several p olypeptides, of which a 15-kDa subacrosomal protein predominated and w as found to be immunocross-reactive with a previously cloned 15-kDa PT protein of the rat (PERF 15) that belongs to a family of lipid-bindin g proteins. A primer pair designed from rat PERF 15 cDNA was then used to screen a mouse testicular cDNA library by polymerase chain reactio n (PCR). The deduced amino acid sequence obtained from the PCR product was almost identical to the testicular-specific rat PERF 15. Developm ental Northern blots and in situ hybridization studies performed with riboprobes encoding the mouse PERF 15 cDNA revealed that mRNA levels w ere highest in round and early elongating mouse spermatids. Immunohist ochemistry indicated that PERF 15 began to be expressed in the cytopla sm of mid-pachytene spermatocytes and appeared to reach maximum expres sion in the distal cytoplasm of late elongating mouse spermatids, long after transcriptional arrest. During the development of round and ear ly elongated spermatids, the immunolabel became progressively concentr ated over the anterior half of the spermatid nucleus, suggesting a sub acrosomal deposition of PERF 15 during this phase of mouse spermiogene sis.