Abstract
Previous studies reported the presence of choline acetyltransferase (ChAT) mRNA and protein in the mammalian testis. We have now found that none of the ChAT mRNAs produced in the testis is capable of encoding a full-length ChAT protein. Two ChAT cDNAs were isolated from an adult rat testis cDNA library encoding N-terminally truncated ChAT proteins of 450 and 414 amino acids (aa), respectively, the former containing a novel N-terminal extension of 69 residues. Rapid Amplification of cDNA Ends (RACE) analysis revealed a complex pattern of 5' untranslated mRNA termini generated from the ChAT gene locus in the testis, all representing truncated versions of the ChAT enzyme. Two of these proteins were produced in transfected fibroblasts and found to lack ChAT activity. Neither did they show binding to the ChAT substrates, acetyl CoA and choline, in a competition assay. These results indicate that mammalian testis lacks a bona fide ChAT enzyme but expresses truncated ChAT proteins with a possible unique function to the testis.
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