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      Insulin-like growth factors and their binding proteins in domestic animals

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      Animal Science

      Cambridge University Press (CUP)

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          Abstract

          Insulin-like growth factors (IGFs) and their binding proteins play an essential role in regulating animal growth and metabolism. The initial portion of the current review focuses on the physiological effects of the IGFs and delineates their role as regulators of animal growth and metabolism. The role of IGFs as mediators of growth hormone effects, as insulin-like metabolic regulators and as foetal growth regulators is discussed. The remainder of the review is devoted to the IGF binding proteins, their modulation of IGF action and their role in foetal and postnatal regulation of growth.

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          Most cited references 121

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          A growth-deficiency phenotype in heterozygous mice carrying an insulin-like growth factor II gene disrupted by targeting.

          Growth factors are thought to function as pivotal autocrine-paracrine regulatory signals during embryonic development. Insulin-like growth factor II (IGF-II), a mitogenic polypeptide for a variety of cell lines, could have such a role, as indicated by the pattern of expression of its gene during rodent development. The IGF-II gene uses at least three promoters and expresses several transcripts in many tissues during the embryonic and neonatal periods, whereas expression in adult animals is confined to the choroid plexus and the leptomeninges. To examine the developmental role of IGF-II, we have begun to study the consequences of introducing mutations at the IGF-II gene locus in the mouse germ line. We have disrupted one of the IGF-II alleles in cultured mouse embryonic stem (ES) cells by gene targeting and constructed chimaeric animals. Germ-line transmission of the inactivated IGF-II gene from male chimaeras yielded heterozygous progeny that were smaller than their ES cell-derived wild-type littermates (about 60% of normal body weight). These growth-deficient animals were otherwise apparently normal and fertile. The effect of the mutation was exerted during the embryonic period. These results provide the first direct evidence for a physiological role of IGF-II in embryonic growth.
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            Myogenic vector expression of insulin-like growth factor I stimulates muscle cell differentiation and myofiber hypertrophy in transgenic mice.

            The avian skeletal alpha-actin gene was used as a template for construction of a myogenic expression vector that was utilized to direct expression of a human IGF-I cDNA in cultured muscle cells and in striated muscle of transgenic mice. The proximal promoter region, together with the first intron and 1.8 kilobases of 3'-noncoding flanking sequence of the avian skeletal alpha-actin gene directed high level expression of human insulin-like growth factor I (IGF-I) in stably transfected C2C12 myoblasts and transgenic mice. Expression of the actin/IGF-I hybrid gene in C2C12 muscle cells increased levels of myogenic basic helix-loop-helix factor and contractile protein mRNAs and enhanced myotube formation. Expression of the actin/IGF-I hybrid gene in mice elevated IGF-I concentrations in skeletal muscle 47-fold resulting in myofiber hypertrophy. IGF-I concentrations in serum and body weight were not increased by transgene expression, suggesting that the effects of transgene expression were localized. These results indicate that sustained overexpression of IGF-I in skeletal muscle elicits myofiber hypertrophy and provides the basis for manipulation of muscle physiology utilizing skeletal alpha-actin-based vectors.
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              Insulin-like growth factor binding protein 1 stimulates cell migration and binds to the alpha 5 beta 1 integrin by means of its Arg-Gly-Asp sequence.

              Insulin-like growth factor (IGF)-binding protein 1 (IGFBP-1) contains an Arg-Gly-Asp (RGD) integrin recognition sequence. In vitro mutagenesis was used to alter this RGD sequence to Trp-Gly-Asp (WGD). Migration of Chinese hamster ovary (CHO) cells expressing the wild-type protein was more than 3-fold greater in 48 hr compared with cells expressing the WGD mutant form of IGFBP-1. Similarly, wild-type IGFBP-1 added to the media of control CHO cells stimulated migration 2-fold compared with the WGD protein. A synthetic RGD-containing peptide, when added to the medium with wild-type IGFBP-1, blocked the effect of IGFBP-1 on cell migration. The addition of IGF-I to the culture medium had no effect on the migration of cells expressing IGFBP-1 or vector alone. Affinity chromatography of 125I-labeled CHO cell membrane proteins, using IGFBP-1 coupled to agarose, identified the alpha 5 beta 1 integrin (fibronectin receptor) as the only cell surface molecule capable of binding IGFBP-1 in an RGD-dependent manner. Furthermore, wild-type IGFBP-1, but not the WGD mutant form, could be coprecipitated from CHO cells with an antibody directed against the alpha 5 integrin subunit. These studies demonstrate that IGFBP-1 stimulates CHO cell migration and binds to the alpha 5 beta 1 integrin receptor, both by an RGD-dependent mechanism. The effect of IGFBP-1 on migration is independent of IGF-I and is probably mediated through the alpha 5 beta 1 integrin.
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                Author and article information

                Journal
                Animal Science
                Anim. Sci.
                Cambridge University Press (CUP)
                1357-7298
                1748-748X
                February 1997
                September 02 2010
                February 1997
                : 64
                : 1
                : 1-15
                Article
                10.1017/S1357729800015502
                © 1997

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