Evolution of insulin-like growth factor I (IGF-I)

Structure and expression of an IGF-I precursor from Xenopus laevis

Yoshitaka Kajimoto, Peter Rotwein

Research output: Contribution to journalArticle

57 Citations (Scopus)

Abstract

By means of a cloning strategy employing the polymerase chain reaction, we have isolated and characterized cDNAs for Xenopus laevis insulin-like growth factor I (IGF-I). These cDNAs encode a primary IGF-I translation product of 153 residues that demonstrates considerable amino acid sequence similarity with IGF-IA peptides from other species. Fifty-seven of 70 residues of the mature protein are identical among human, rat, chicken, and Xenopus IGF-I, while less amino acid conservation is found at the COOH-terminus (25/35 identities) or at the NH2-terminus (24/48 identities) of the precursor protein. Despite the lower degree of structural similarity at the NH2-terminus, in vitro studies of IGF-I biosynthesis and proteolytic processing support a conserved function for the atypically long 48 residue NH2-terminal signal sequence in directing the nascent IGF-I peptide through the secretory pathway. The 5′-untranslated region of Xenopus IGF-I mRNA matches the human, rat, and chicken sequences in greater than 90% of 279 nucleotides. IGF-I mRNAs from all four species encode a conserved upstream open reading frame of 14 amino acids starting 240-250 nucleotides 5′ to the translation start site, suggesting a possible role for this region in modulating IGF-I gene expression. The X. laevis IGF-I gene is transcribed and processed into three mRNAs of 1.6, 2.1, and 3.0 kilobases in liver, and IGF-I mRNAs can be detected in liver, lung, heart, kidney, and peritoneal fat of adult animals. These studies demonstrate that both the IGF-I protein precursor and potential regulatory regions of IGF-I mRNA have been conserved during vertebrate evolution, and indicate that like several other polypeptide growth factors, IGF-I may be of fundamental importance in regulating specific aspects of growth and development in all vertebrates.

Original languageEnglish (US)
Pages (from-to)217-226
Number of pages10
JournalMolecular Endocrinology
Volume4
Issue number2
StatePublished - Feb 1990
Externally publishedYes

Fingerprint

Xenopus laevis
Insulin-Like Growth Factor I
Messenger RNA
Protein Precursors
Xenopus
Peptides
Vertebrates
Chickens
Nucleotides
Complementary DNA
Amino Acids
Nucleic Acid Regulatory Sequences
5' Untranslated Regions
Secretory Pathway
Liver
Protein Sorting Signals
Growth and Development
Open Reading Frames
Organism Cloning
Amino Acid Sequence

ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology, Diabetes and Metabolism

Cite this

Evolution of insulin-like growth factor I (IGF-I) : Structure and expression of an IGF-I precursor from Xenopus laevis. / Kajimoto, Yoshitaka; Rotwein, Peter.

In: Molecular Endocrinology, Vol. 4, No. 2, 02.1990, p. 217-226.

Research output: Contribution to journalArticle

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