title: Evolutionary conservation of the insulin gene structure in invertebrates: cloning of the gene encoding molluscan insulin-related peptide III from Lymnaea stagnalis.
abstract: Although insulins and structurally related peptides are found in vertebrates as well as in invertebrates, it is not clear whether the genes encoding these hormones have emerged from a single ancestral (insulin)-type of gene or, alternatively, have arisen independently through convergent evolution from different types of gene. To investigate this issue, we cloned the gene encoding the molluscan insulin-related peptide III (MIP III) from the freshwater snail, Lymnaea stagnalis. The predicted MIP III preprohormone had the overall organization of preproinsulin, with a signal peptide and A and B chains, connected by two putative C peptides. Although MIP III was found to share key features with vertebrate insulins, it also had unique structural characteristics in common with the previously identified MIPs I and II, thus forming a distinct class of MIP peptides within the insulin superfamily. MIP III is synthesized in neurones in the brain. It is encoded by a gene with the overall organization of the vertebrate insulin genes, with three exons and two introns, of which the second intron interrupts the coding region of the C peptides. Our data therefore demonstrate that in the Archaemetazoa, the common ancestor of the vertebrates and invertebrates, a primordial peptide with a two-chain insulin configuration encoded by a primordial insulin-type gene must have been present.
authors.affiliation: Faculty of Biology, Vrije Universiteit, Amsterdam, The Netherlands.
authors.forename: A B
authors.initials: AB
authors.lastname: Smit
authors.forename: A
authors.initials: A
authors.lastname: van Marle
authors.forename: R
authors.initials: R
authors.lastname: van Elk
authors.forename: J
authors.initials: J
authors.lastname: Bogerd
authors.forename: H
authors.initials: H
authors.lastname: van Heerikhuizen
authors.forename: W P
authors.initials: WP
authors.lastname: Geraerts
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers; D005091:Exons; D015698:Genomic Library; D006801:Humans; D017403:In Situ Hybridization; D007328:Insulin / Q000235:genetics*; D007438:Introns; D007447:Invertebrate Hormones / Q000096:biosynthesis / Q000235:genetics*; D007448:Invertebrates / Q000235:genetics*; D008195:Lymnaea / Q000235:genetics*; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000235:genetics; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D014714:Vertebrates / Q000235:genetics
chemical_list: D017931:DNA Primers; D007328:Insulin; D007447:Invertebrate Hormones; D011498:Protein Precursors; C084389:insulin-related peptide III, Lymnaea