The adult rodent epididymis and seminal vesicles were shown by polymerase chain reaction (PCR) cloning. Northern blot analysis, and in situ hybridization to be major expression sites of an mRNA encoding a small glycosylphosphatidylinositol (GPI)-anchored cell surface antigen that has been previously described as the mouse lymphocyte differentiation antigen B7, herein referred to as MB7. Sequence comparison of the corresponding epididymal cDNAs from the mouse (MB7) and the rat (RB7) revealed an unexpected divergence in the peptide coding regions of these homologous genes. A possible functional relationship to the human sperm surface and lymphocyte differentiation antigen CDw52/HE5 is discussed with respect to the highly variable mature peptide coding regions.
