title: Duplication of the IGFBP-2 gene in teleost fish: protein structure and functionality conservation and gene expression divergence.
abstract: BACKGROUND
  Insulin-like growth factor binding protein-2 (IGFBP-2) is a secreted protein that binds and regulates IGF actions in controlling growth, development, reproduction, and aging. Elevated expression of IGFBP-2 is often associated with progression of many types of cancers.
  
  
  RESULTS
  We report the identification and characterization of two IGFBP-2 genes in zebrafish and four other teleost fish. Comparative genomics and structural analyses suggest that they are co-orthologs of the human IGFBP-2 gene. Biochemical assays show that both zebrafish igfbp-2a and -2b encode secreted proteins that bind IGFs. These two genes exhibit distinct spatiotemporal expression patterns. During embryogenesis, IGFBP-2a mRNA is initially detected in the lens, then in the brain boundary vasculature, and subsequently becomes highly expressed in the liver. In the adult stage, liver has the highest levels of IGFBP-2a mRNA, followed by the brain. Low levels of IGFBP-2a mRNA were detected in muscle and in the gonad in male adults only. IGFBP-2b mRNA is detected initially in all tissues at low levels, but later becomes abundant in the liver. In adult males, IGFBP-2b mRNA is only detected in the liver. In adult females, it is also found in the gut, kidney, ovary, and muscle. To gain insights into how the IGFBP-2 genes may have evolved through partitioning of ancestral functions, functional and mechanistic studies were carried out. Expression of zebrafish IGFBP-2a and -2b caused significant decreases in the growth and developmental rates and their effects are comparable to that of human IGFBP-2. IGFBP-2 mutants with altered IGF binding-, RGD-, and heparin-binding sites were generated and their actions examined. While mutating the RGD and heparin binding sites had little effect, altering the IGF binding site abolished its biological activity.
  
  
  CONCLUSIONS
  These results suggest that IGFBP-2 is a conserved regulatory protein and it inhibits growth and development primarily by binding to and inhibiting IGF actions in vivo. The duplicated IGFBP-2 genes may provide additional flexibility in the regulation of IGF activities.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Zhou
authors.forename: Wenhong
authors.initials: W
authors.lastname: Li
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Kamei
authors.forename: Cunming
authors.initials: C
authors.lastname: Duan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019521:Body Patterning; D019070:Cell Lineage; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D047108:Embryonic Development; D019143:Evolution, Molecular; D005399:Fishes / Q000235:genetics*; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D014644:Genetic Variation; D006493:Heparin / Q000378:metabolism; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000737:chemistry* / Q000235:genetics*; D016023:Integrins / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D011485:Protein Binding; D013002:Somatomedins / Q000378:metabolism; D026801:Synteny; D015027:Zebrafish / Q000196:embryology / Q000235:genetics
chemical_list: D018971:Insulin-Like Growth Factor Binding Protein 2; D016023:Integrins; D013002:Somatomedins; D006493:Heparin