title: Switching to fast growth: the insulin-like growth factor (IGF) system in skeletal muscle of Atlantic salmon.
abstract: In this study we describe the complete coding sequence for insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), insulin-like growth factor binding protein (IGFBP) 1, 2, 4, 5 and 6 and IGFBP-related protein 1 (IGFBP-rP1) of Atlantic salmon (Salmo salar L.). We also report the characterisation of two gene paralogues of IGFBP-2 and IGFBP-5. Following 22 days restricted feeding (0 d) to achieve zero growth, fish were fed to satiation and sampled at 3, 5, 7, 14, 30 and 60 days. Expression profiles for genes involved in the IGF signalling pathway in fast myotomal muscle were determined using real-time quantitative RT-PCR. The transition from zero to fast growth is characterised by constitutive upregulation of IGF-I and IGFBP-4, a transient increase in IGFBP-5.2, and downregulation of IGFBP-2.1, IGF-II, IGF2R (IGF-II receptor) and IGFR1a (IGF-I receptor a). Expression of IGFBP-2.2, IGFBP-5.1, IGFBP-6, IGFBP-rP1 and IGFR1b showed little or no response to feeding. Expression of the myogenic marker genes myogenin, MHC and MLC2 were higher with feed restriction, and decreased as an early response to feeding, before increasing to a peak at 14 days, corresponding with a peak in IGF-I expression. IGFBP-4, which contains a putative connective tissue localisation signal, was the only IGFBP constitutively upregulated following feeding, and was positively correlated with IGF-I expression. Together, these data show that switching to fast growth in Atlantic salmon skeletal muscle involves the local upregulation of IGF-I, IGFBP-5.2 and IGFBP-4, with downregulation of IGFBP-2.1.
authors.affiliation: Gatty Marine Laboratory, School of Biology, University of St Andrews, St Andrews, Fife KY16 8LB, UK.
authors.forename: Neil I
authors.initials: NI
authors.lastname: Bower
authors.forename: Xuejun
authors.initials: X
authors.lastname: Li
authors.forename: Richard
authors.initials: R
authors.lastname: Taylor
authors.forename: Ian A
authors.initials: IA
authors.lastname: Johnston
mesh_terms: D000595:Amino Acid Sequence; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018969:Insulin-Like Growth Factor Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism*; D009752:Nutritional Status; D020317:Salmo salar / Q000254:growth & development* / Q000378:metabolism*; D015398:Signal Transduction; D013002:Somatomedins / Q000378:metabolism*; D013997:Time Factors
chemical_list: D029941:Fish Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins