Novel transcripts of carbonic anhydrase II in mouse and human testis

Intracellular and extracellular sources of bicarbonate are essential for sp erm motility, sperm binding to the zona pellucida and the acrosome reaction . Carbonic anhydrase II, catalysing the synthesis of bicarbonate within spe rmatozoa, must play a significant role in these mechanisms, We report here the expression of carbonic anhydrase II during mouse spermatogenesis and th e primary structure of testicular transcripts coding for carbonic anhydrase II isolated from adult mouse and human testes, The mouse carbonic anhydras e II (Car2) mRNA displays a 5' untranslated region (UTR) larger than the co rresponding somatic sequence. The additional 5' sequence contains the 'TATA box' used in somatic tissues and other promoter sequences, suggesting the use of testis-specific promoters further upstream with read-through of down stream promoters, The 3'UTR of the Car2 mRNA is shorter in mature testicula r cells than in somatic cells. Polysomal gradient analysis of carbonic anhy drase II transcripts isolated from adult mouse testis and kidney revealed d ifferent translation potential: most of the testicular transcripts were pre sent in the non-polysomal fractions, whereas a considerable fraction of kid ney transcripts were polysome-associated, These results suggest that specif ic transcriptional and post-transcriptional mechanisms regulate the express ion of carbonic anhydrase II during mammalian spermatogenesis.