Variants of the 5 '-untranslated region of the bovine growth hormone receptor mRNA: isolation, expression and effects on translational efficiency

The growth hormone receptor (GHR) gene in cattle is expressed as multiple G HR mRNA variants that differ in the 5'-untranslated region (5'-UTR). Three GHR mRNA 5'-UTR variants (named 1A, 1B, and 1C)were isolated in previous st udies. Six additional GHR mRNA 5'-UTR variants (named 1D, 1E, 1F, 1G, 1H, a nd 1I) were discovered in the present study by using rapid amplification of cDNA ends (RACE). Ribonuclease protection assays (RPA) indicated that vari ant 1A was exclusively expressed in liver, variant 1F was expressed in live r and muscle, and most of the remaining GHR 5'-UTR variants were expressed in a variety of tissues including liver and muscle. The RPA also indicated that in liver and skeletal muscle, two important GH target tissues, the mos t abundant GHR mRNA 5'-UTR variants were 1A and 1B (liver) and 1B and 1C (m uscle), respectively. In vitro translation assays indicated that the GHR 5' -UTR variants also differed in their effects on the translation of a lucife rase reporter mRNA. Notably, the GHR 5'-UTR 1B, which is a highly expressed GHR 5'-UTR variant in vivo, strongly inhibited translation of the lucifera se reporter mRNA. The observations in the present study suggest that GHR ex pression in the bovine may be controlled by translational mechanisms in add ition to complex transcriptional mechanisms. (C) 2001 Elsevier Science B.V. All rights reserved.