Endocrine effects of growth hormone overexpression in transgenic coho salmon P.A. Raven a , M. Uh a , D. Sakhrani a , B.R. Beckman b , K. Cooper b , J. Pinter a , E.H. Leder c , J. Silverstein d , R.H. Devlin a, * a Department of Fisheries & Oceans, Centre for Aquaculture & Environmental Research, 4160 Marine Drive, West Vancouver, BC, Canada V7V 1N6 b Northwest Fisheries Science Center, Seattle, WA 98112-2097, USA c Division of Genetics and Physiology, Department of Biology, 20014 University of Turku, Finland d United States Department of Agriculture, Agricultural Research Service, Aquaculture, Beltsville, MD 20705, USA article info Article history: Received 8 May 2008 Revised 22 July 2008 Accepted 23 July 2008 Available online 5 August 2008 Keywords: Growth hormone Transgenic Coho salmon Oncorhynchus kisutch Insulin-like growth factor-I Growth hormone receptor Growth hormone releasing hormone Neuropeptide Y Cholecystokinin Cartilage sulphation abstract Non-transgenic (wild-type) coho salmon (Oncorhynchus kisutch), growth hormone (GH) transgenic sal- mon (with highly elevated growth rates), and GH transgenic salmon pair fed a non-transgenic ration level (and thus growing at the non-transgenic rate) were examined for plasma hormone concentrations, and liver, muscle, hypothalamus, telencephalon, and pituitary mRNA levels. GH transgenic salmon exhibited increased plasma GH levels, and enhanced liver, muscle and hypothalamic GH mRNA levels. Insulin-like growth factor-I (IGF-I) in plasma, and growth hormone receptor (GHR) and IGF-I mRNA levels in liver and muscle, were higher in fully fed transgenic than non-transgenic fish. GHR mRNA levels in transgenic fish were unaffected by ration-restriction, whereas plasma GH was increased and plasma IGF-I and liver IGF-I mRNA were decreased to wild-type levels. These data reveal that strong nutritional modulation of IGF-I production remains even in the presence of constitutive ectopic GH expression in these transgenic fish. Liver GHR membrane protein levels were not different from controls, whereas, in muscle, GHR levels were elevated approximately 5-fold in transgenic fish. Paracrine stimulation of IGF-I by ectopic GH pro- duction in non-pituitary tissues is suggested by increased basal cartilage sulphation observed in the transgenic salmon. Levels of mRNA for growth hormone-releasing hormone (GHRH) and cholecystokinin (CCK) did not differ between groups. Despite its role in appetite stimulation, neuropeptide Y (NPY) mRNA was not found to be elevated in transgenic groups. Crown Copyright Ó 2008 Published by Elsevier Inc. All rights reserved. 1. Introduction Growth in fish is influenced by a complex set of cellular, hor- monal and environmental factors which play roles in determining many secondary characteristics such as feeding behaviour, meta- bolic efficiency, and reproductive age and size. In nature, growth is affected by seasonal variation in food supplies and environmental parameters such as temperature and photoperiod, and thus regula- tion of organismal signals to match available energy supplies is an important adaptive response to maximize fitness in the wild. In aquaculture, enhancing growth is a key objective to improve pro- duction efficiency, and many strains of fishes have now undergone domestication and/or directed selection for enhanced growth rate. Growth hormone (GH) gene transgenesis has also been used in sev- eral fish species to enhance growth, in some cases dramatically (Du et al., 1992; Devlin et al., 1994a, 1995a; Hinits and Moav, 1999; Pit- kanen et al., 1999; Rahman and Maclean, 1999; Morales et al., 2001; Nam et al., 2001; Lu et al., 2002). This technology has not yet been adopted for use in commercial aquaculture, however, transgenic strains provide useful model systems for studying the conse- quences of growth enhancement from genetic, physiological and ecological standpoints (Chatakondi et al., 1995; Fu et al., 1998, 2000; Stevens et al., 1999; Martinez et al., 2000; Stevens and Devlin, 2000; Rahman et al., 2001; Dunham et al., 2002; Sundström et al., 2003, 2004a, 2004b; Tymchuk et al., 2005; Raven et al., 2006). GH transgenic salmonids show growth rates (2–3-fold enhance- ment in daily weight gain) which can result in large differences in size from control animals after several months (Du et al., 1992; Devlin et al., 1994a, 2004). To achieve this growth rate, transgenic salmon have enhanced appetites, feeding motivation, nutritional set points, and enhanced feed conversion efficiencies (Abrahams and Sutterlin, 1999; Devlin et al., 1999; Cook et al., 2000; Sun- dström et al., 2003, 2004b; Raven et al., 2006; Oakes et al., 2007) which result in accelerated development and earlier maturation age (Devlin et al., 1999, 2000, 2004; Sundström et al., 2003, 2004a). While the enhanced growth rate in these fish results from production of elevated GH (Devlin et al., 1994a, 2000; Kang and Devlin, 2004) arising from transgene expression throughout the body (Mori and Devlin, 1999), the precise hormonal and neuroen- docrine mechanisms controlling increased growth rate and associ- ated appetite in these fish are unknown, and brain and pituitary 0016-6480/$ - see front matter Crown Copyright Ó 2008 Published by Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2008.07.011 * Corresponding author. Fax: +1 604 666 3497. E-mail address: Robert.Devlin@dfo-mpo.gc.ca (R.H. Devlin). General and Comparative Endocrinology 159 (2008) 26–37 Contents lists available at ScienceDirect General and Comparative Endocrinology journal homepage: www.elsevier.com/locate/ygcen