Cloning of ovine insulin-like growth factor-I cDNAs: heterogeneity in the mRNA population.
We have isolated and characterized lamb liver cDNAs encoding ovine insulin-like growth factor-I (oIGF-I) precursor polypeptide to study IGF-I gene expression in ruminants. Four cDNA clones were sequenced revealing two different exon 1 sequences (designated 1A and 1B) and four different putative poly(A) adenylation sites. cDNAs containing exon 1A or exon 1B encode precursor polypeptides of 138 or 154 amino acids, respectively. A 130-amino-acid peptide is encoded by all cDNAs examined. These precursors include a hydrophobic leader peptide of varying lengths, the 70-amino-acid oIGF-I, and a 35-amino-acid carboxyl terminal extension peptide. The predicted amino acid sequence of the oIGF-I peptide differs from the human, bovine, and porcine IGF-Is at a single amino acid (at position 66, alanine is substituted for proline) and differs from rat and mouse IGF-Is at 4 and 5 positions, respectively. Both the amino- and carboxy-terminal extension peptides showed regions of extensive sequence homology. Ovine IGF-I amino-terminal peptides are 1 amino acid longer than other mammalian IGFs due to the presence of an extra amino acid (glutamine) present at the proposed boundary of exon 1 and exon 2. Northern blot analysis revealed multiple oIGF-I transcripts in a broad band at 800-1,100 nucleotides and other transcripts of higher molecular weight in liver. There was no detectable expression in either spleen or brain.
Wong
E A
EA
Department of Animal Science, University of Minnesota, St. Paul 55108.
Ohlsen
S M
SM
Godfredson
J A
JA
Dean
D M
DM
Wheaton
J E
JE
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D003001:Cloning, Molecular; D004247:DNA; D005091:Exons / Q000235:genetics; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D011061:Poly A / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D012689:Sequence Homology, Nucleic Acid; D012756:Sheep / Q000235:genetics; D013002:Somatomedins / Q000235:genetics*; D013552:Swine
D012333:RNA, Messenger; D013002:Somatomedins; D011061:Poly A; D007334:Insulin-Like Growth Factor I; D004247:DNA