Synthesis and glycosylation of CD52, the major 'maturation-associated' antigen of rat spermatozoa, in the cauda epididymidis

A western and lectin blot analysis was performed of the major 'maturation-a ssociated' antigen of rat spermatozoa, which is the rat counterpart of huma n CD52. In the absence of a suitable antibody, direct study of this approxi mately 26 kDa antigen, named previously SMemG, had been difficult. In the p resent study, these problems were overcome by raising a polyclonal antibody against a chemosynthetic peptide predicted from the cDNA sequence of the a ntigen. The antibody the cDNA bound to a glycoprotein of rat cauda epididym idal tissue and spermatozoa, this glycoprotein was cleaved by phosphatidyli nositol-specific phospholipase C and, after deglycosylation, was reduced to approximately 6 kDa. Northern blot analysis confirmed that the CD52 mRNA w as transcribed only post-testicularly, and antibody binding to testicular a nd sperm proteins of different molecular masses was shown to be nonspecific . Flow cytometry also indicated that the antigen was inserted into the sper m membrane during epididymal transit. Moreover, despite the presence of CD5 2 mRNA in all parts of the rat epididymis, only the 'long' mRNA molecules o f the cauda region were efficiently translated and the antigen glycosylated , indicating that expression of rat CD52 is regulated on a post-transcripti onal level, Lectin binding and deglycosylation studies supported the conten tion that there is extensive mucin-type O-glycosylation of rat CD52. In rat s, there was no indication of complex N-linked carbohydrates similar to tho se described for human CD52.