Isolation and characterization of a cDNA clone encoding ovine type I carbonic anhydrase

To identify genes involved in the postnatal development of sheep ruminal epithelium, a lambda gt22a cDNA library was constructed from poly(A)+ RNA isolated from mature sheep ruminal epithelium. A plus/minus screening procedure was used to identify genes expressed in mature but not in neonatal ruminal epithelium. One of the cDNA clones isolated encodes an ovine carbonic anhydrase, based on nucleotide and deduced peptide sequence analysis. The deduced peptide is most closely related to eukaryotic type I carbonic anhydrase, based on comparison with all available carbonic anhydrase sequences. Northern blot hybridization confirmed that the amount of mRNA complementary to the carbonic anhydrase cDNA clone is more than five times higher in ruminal epithelium for mature sheep (12 wk old) than in ruminal epithelium from neonatal lambs (< 12h old). Messenger RNA complementary to this cDNA clone was found only in the epithelium of the ruminant forestomach compartments (i.e., rumen, reticulum, and omasum), but small amounts of hybridizable mRNA were also found in sheep skin. This carbonic anhydrase cDNA clone will allow the study of transcriptional regulation of the carbonic anhydrase gene during ruminal epithelial development.