Journal Article

Transcriptional Regulation of the IGF Signaling Pathway by Amino Acids and Insulin-Like Growth Factors during Myogenesis in Atlantic Salmon

Bower, Neil I., Johnston, Ian A.

2010

Overview

The insulin-like growth factor signalling pathway is an important regulator of skeletal muscle growth. We examined the mRNA expression of components of the insulin-like growth factor (IGF) signalling pathway as well as Fibroblast Growth Factor 2 (FGF2) during maturation of myotubes in primary cell cultures isolated from fast myotomal muscle of Atlantic salmon (Salmo salar). The transcriptional regulation of IGFs and IGFBP expression by amino acids and insulin-like growth factors was also investigated. Proliferation of cells was 15% d(-1) at days 2 and 3 of the culture, increasing to 66% d(-1) at day 6. Three clusters of elevated gene expression were observed during the maturation of the culture associated with mono-nucleic cells (IGFBP5.1 and 5.2, IGFBP-6, IGFBP-rP1, IGFBP-2.2 and IGF-II), the initial proliferation phase (IGF-I, IGFBP-4, FGF2 and IGF-IRb) and terminal differentiation and myotube production (IGF2R, IGF-IRa). In cells starved of amino acids and serum for 72 h, IGF-I mRNA decreased 10-fold which was reversed by amino acid replacement. Addition of IGF-I and amino acids to starved cells resulted in an 18-fold increase in IGF-I mRNA indicating synergistic effects and the activation of additional pathway(s) leading to IGF-I production via a positive feedback mechanism. IGF-II, IGFBP-5.1 and IGFBP-5.2 expression was unchanged in starved cells, but increased with amino acid replacement. Synergistic increases in expression of IGFBP5.2 and IGFBP-4, but not IGFBP5.1 were observed with addition of IGF-I, IGF-II or insulin and amino acids to the medium. IGF-I and IGF-II directly stimulated IGFBP-6 expression, but not when amino acids were present. These findings indicate that amino acids alone are sufficient to stimulate myogenesis in myoblasts and that IGF-I production is controlled by both endocrine and paracrine pathways. A model depicting the transcriptional regulation of the IGF pathway in Atlantic salmon muscle following feeding is proposed.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Amino acids / Amino Acids - physiology / Animals / Base Sequence / Cell culture / Cell proliferation / DNA Primers / Fibroblast growth factor / Fibroblast growth factor 2 / Fibroblast growth factors / Fish / Gene expression / Gene Expression Regulation - physiology / Gene regulation / Genes / Genetic aspects / Growth factors / Insulin / Insulin-like growth factor I / Insulin-like growth factor II / Insulin-like growth factor II receptors / Insulin-like growth factor-binding protein 2 / Insulin-like growth factor-binding protein 4 / Insulin-like growth factor-binding protein 5 / Insulin-like growth factor-binding protein 6 / Insulin-like growth factors / Kinases / Marine and Aquatic Sciences / Maturation / Molecular Biology / Myoblasts / Myogenesis / Myotubes / Oncorhynchus mykiss / Paracrine signalling / Physiology/Endocrinology / Physiology/Genomics / Polymerase Chain Reaction / Positive feedback / RNA / Rodents / Salmo salar / Salmon / Signal transduction / Signal Transduction - physiology / Skeletal muscle / Somatomedins - physiology / Synergistic effect / Synergistic effects / Transcription / Transcription (Genetics) / Transcription, Genetic - physiology / Zebrafish