Catfish express two forms of insulin-like growth factor-I (IGF-I) in the brain. Ubiquitous IGF-I and brain-specific IGF-I.
Insulin-like growth factor-I (IGF-I) is expressed not only in liver, but also in brain and other tissues. This ubiquitous IGF-I has a complex pattern of expression due to multiple transcription start sites, polyadenylation sites and exon skipping. We have isolated a cDNA encoding a brain-specific IGF-I from a catfish brain cDNA library. Also, a fragment encoding ubiquitous IGF-I was amplified from brain and liver mRNA and the deduced protein shown to be distinct (66% sequence identity) from brain-specific IGF-I. Consistent with other IGF-I prepropeptides, the brain-specific IGF-I has a 43-residue signal peptide followed by B, C, A, D, and E domains. Retained in the catfish brain-specific IGF-I peptide are residues predicted to be involved with the correct tertiary folding, disulfide linkages, and receptor binding. Northern blot analysis of poly(A+)-rich mRNA from brain indicated a single 1600-base pair transcript; a band was not detected from mRNA of liver, stomach, pancreas, pituitary, blood, herring brain, or brain poly(A-) RNA. A sensitive reverse transcriptase/polymerase chain reaction assay also showed that brain-specific IGF-I mRNA was expressed solely in the Thai catfish brain but not liver, stomach, pancreas, pituitary, ovary, and African catfish brain.
McRory
J E
JE
Department of Biology, University of Victoria, British Columbia, Canada.
Sherwood
N M
NM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D001921:Brain / Q000378:metabolism*; D002397:Catfishes; D017931:DNA Primers; D018076:DNA, Complementary / Q000378:metabolism; D005399:Fishes; D015870:Gene Expression; D015723:Gene Library; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D011061:Poly A / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; D011061:Poly A; D007334:Insulin-Like Growth Factor I