Duplicate insulin-like growth factor-I genes in salmon display alternative splicing pathways.
Insulin-like growth factor (IGF-I) is a single chain, 70-amino acid, peptide hormone, which is essential to the process of growth and differentiation in higher vertebrates. IGF-I exhibits a very high degree of conservation throughout vertebrate evolution, and recent studies in fish have shown improved rates of growth in salmonids treated with exogenous recombinant mammalian IGF-I, implying a role for this hormone in fish similar to that in mammals. This paper reports the identification and sequencing of four different liver-derived cDNAs encoding IGF-I from chinook salmon, Oncorhynchus tshawytscha. The different cDNAs all contain sequences that encode an identical mature IGF-I protein. The differences between the four cDNAs are of two types: 1) single basepair changes and 2) additional blocks of sequence occurring at one site within the E-domain regions of three of the four cDNAs. The sequence data indicate that each of the cDNAs identified was transcribed from a different IGF-I gene, and analysis of the chinook salmon genome by Southern blotting supports the existence of four distinct IGF-I genes and suggests that there are at least two IGF-I loci in salmon. Although, analysis of total RNA from salmonid liver identifies only a single major transcript of 4200 nucleotides, polymerase chain reaction analysis suggests the presence of two structurally different salmonid IGF-I genes with the potential for multiple splicing alternatives of the IGF-I transcript.
Wallis
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AE
Monsanto Canada, Inc., Streetsville, Mississauga, Ontario.
Devlin
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RH
D017398:Alternative Splicing / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004247:DNA / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D016133:Polymerase Chain Reaction; D012313:RNA / Q000032:analysis / Q000302:isolation & purification; D012474:Salmon / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D012313:RNA; D007334:Insulin-Like Growth Factor I; D004247:DNA