Multiple Forms of Gamma-Glutamyl Transpeptidase Messenger Ribonucleic Acid are Expressed in the Adult Rat Testis and Epididymis1

The expression of gamma-glutamyl transpeptidase (GGT) mRNA in tissues of the adult rat male reproductive tract was examined. Northern blot analysis of total RNA revealed that GGT mRNA expression occurs primarily in the initial segment and caput epididymidis. Multiple GGT mRNAs of varying sizes were detected in the testis and in different regions of the epididymis: testis, 2.4 and 2.8 kb; efferent ducts, 2.2 and 2.5 kb; initial segment, 2.2, 2.4, and 2.5 kb; caput, 2.2, 2.4, and 2.5 kb; corpus, 2.2 and 2.5 kb; cauda, 2.2 and 2.5 kb; ductus deferens, 2.2 and 2.4 kb. Ribonuclease (RNase) H removal of the poly(A) tail from testicular and epididymal GGT mRNA revealed that multiple GGT mRNAs were not generated by differences in the length of the poly(A) tail. Northern blot analysis of poly(A)+ mRNA with four GGT mRNA 5' untranslated region (UTR)-specific cRNA probes showed that the multiple GGT mRNAs expressed in the testis and epididymis were due to differences in the lengths and nucleotide compositions of the 5' UTR. We hypothesize that transcription of multiple GGT mRNAs from different promoters on the single-copy GGT gene is the molecular basis that underlies the region-specific expression of GGT mRNAs along the rat male reproductive tract.