title: Three insulin-relaxin-like genes in Ciona intestinalis.
abstract: The Ciona intestinalis genome harbors three insulin-like genes: INS-L1, -L2 and -L3. Conserved synteny between the Ciona-human genomes predicts that Ciona INS-Ls are orthologous to the vertebrate insulin-relaxin family, but this relation cannot be inferred from molecular phylogeny. A conserved protein core with six cysteines; typical arrangement of B-, C- and A-protein domains; pro-protein maturation mode; and putative insulin receptor-binding sites were identified in Ciona INS-L proteins. ESTs used to assemble exonic sequences of INS-Ls combined with qRT-PCR analysis provided evidence that the predicted genes are expressed in the developing and adult Ciona. Our results support that Ciona INS-L1 is orthologous to the vertebrate insulin-like/relaxin genes, INS-L2 to insulin genes and INS-L3 to IGF genes. Our analysis also implies that the insulin-like/relaxin ancestor switched receptor type from tyrosine kinase- to GPCR-type, whereas insulin-IGF subfamily retained the tyrosine kinase-type of receptor. We propose that this receptor-switch occurred after the time when urochordates branched from the common chordate lineage, but before the two genome-duplications at the root of the vertebrates.
authors.affiliation: Department of Neuroscience, Unit for Developmental Neuroscience, Uppsala University, BMC, Box 587, S-751 23 Uppsala, Sweden.
authors.forename: Robert Piotr
authors.initials: RP
authors.lastname: Olinski
authors.forename: Carl
authors.initials: C
authors.lastname: Dahlberg
authors.forename: Mike
authors.initials: M
authors.lastname: Thorndyke
authors.forename: Finn
authors.initials: F
authors.lastname: Hallböök
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002938:Ciona intestinalis / Q000235:genetics*; D019143:Evolution, Molecular; D020440:Gene Duplication; D006801:Humans; D007328:Insulin / Q000235:genetics*; D008969:Molecular Sequence Data; D036361:Peptide Hormones / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D012065:Relaxin / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: D007328:Insulin; D036361:Peptide Hormones; D012065:Relaxin