Submitted to: Biochimica et Biophysica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2005
Publication Date: 12/20/2005
Citation: Clay, L.A., Wang, S.Y., Wolters, W.R., Peterson, B.C., Waldbieser, G.C. 2005. Molecular Characterization of the Insulin-Like Growth Factor-i (IGF-I) Gene in Channel Catfish (Ictalurus punctatus). Biochimica et Biophysica Acta - Gene Structure and Expression. 1731(3):139-148. Interpretive Summary: Molecular pathways that control growth in bony fish often differ from mammalian pathways that are more well known. Research in the channel catfish growth hormone-insulin like growth factor pathway was limited by a lack of characterization of the insulin like growth factor 1 (IGF-1) gene. Using molecular cloning techniques, we obtained the IGF-1 genomic sequence, determined this gene was expressed primarily in liver tissue, and also identified IGF-1 DNA sequence variation in catfish populations. This information will permit researchers to determine the role of IGF-1 in lean growth in catfish, and identify DNA sequence variants that may be linked to improved lean growth in selected catfish populations.
Technical Abstract: The insulin-like growth factor I (IGF-I) gene was identified in channel catfish. Partial cDNA sequence, missing exon 1 and part of exon 2, was obtained by 5'- and 3'-RACE experiments using degenerate primers designed from highly conserved vertebrate IGF-I sequences. Direct sequencing of two bacterial artificial chromosome clones provided the remaining gene sequence through 640 bp (basepairs) upstream of the initiator methionine. The genomic sequence revealed a putative TATA box 506 bp upstream of the initiator methionine. The channel catfish IGF-I coding region consisted of 477 bp and contained five exons interrupted by four introns. It encoded a 159 amino acid (aa) pre-propeptide similar to IGF-I in other species. The sequence encoding the signal peptide was 70% G+C with the potential for a stable stem-loop structure (delta G = -64.4 kcal/mole at 27ºC). This region was always excised from full-length cDNA clones transfected into recombination-competent DH5 alpha strain E. coli. However, full-length cDNA was always maintained in recombination-deficient DH10B strain E. coli. Levels of IGF-I mRNA in liver were significantly higher (P < 0.05) than brain, muscle, heart, and kidney; levels in brain and muscle were significantly higher (P < 0.05) than heart and kidney; and levels in heart and kidney were not significantly different. A CT/GA dinucleotide microsatellite in intron 1 was highly polymorphic in commercial channel catfish, and permitted placement of the IGF-I gene 17.3 cM from the IpCG0011 locus in linkage group U19.