Cloning and characterization of the bovine class 1 and class 2 insulin-like growth factor-I mRNAs.
Insulin-like growth factor-I (IGF-I) is an important regulator of growth, development, and metabolism, and is the primary mediator of the growth-promoting activity of growth hormone (GH) in animals. In several species, the IGF-I polypeptide is generated from IGF-I mRNA containing either exon 1 (class 1 IGF-I mRNA) or exon 2 (class 2 IGF-I mRNA) as the leader exon. The objectives of this study were to identify class 1 and class 2 IGF-I mRNAs in cattle and to compare their expression in different tissues, their response to GH, and their translational efficiency. Three class 1 IGF-I cDNAs corresponding to three different transcription start sites in exon 1 and one class 2 IGF-I cDNA were identified from adult cattle liver using 5'-rapid amplification of cDNA ends (5'-RACE). Both classes of IGF-I mRNAs were expressed in a variety of tissues, with the highest level in liver; class 1 IGF-I mRNA was more abundant than class 2 IGF-I mRNA in all tissues. Six hours after a single intramuscular injection of 500 mg of recombinant bovine GH, class 1 and class 2 IGF-I mRNAs in steer liver were increased by 29% (P=0.07) and 62% (P<0.05), respectively. The luciferase reporter mRNA fused to a class 1 IGF-I 5'-untranslated region (5'-UTR) was translated four times more efficiently in vitro than the luciferase reporter mRNA fused to a class 2 IGF-I 5'-UTR (P<0.05). These results indicate that the IGF-I gene in cattle is transcribed as class 1 and class 2 IGF-I mRNAs and that the two classes of IGF-I mRNAs may be regulated differentially at both transcriptional and translational levels.
Wang
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Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
Price
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Jiang
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D020121:5' Untranslated Regions; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry; D005091:Exons / Q000235:genetics*; D015870:Gene Expression; D013006:Growth Hormone / Q000494:pharmacology; D007273:Injections, Intramuscular; D007334:Insulin-Like Growth Factor I / Q000737:chemistry / Q000235:genetics*; D008099:Liver / Q000737:chemistry; D008156:Luciferases / Q000235:genetics; D008297:Male; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014158:Transcription, Genetic
D020121:5' Untranslated Regions; D018076:DNA, Complementary; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D008156:Luciferases