Distinct organ-specific up- and down-regulation of IGF-I and IGF-II mRNA in various organs of a GH-overexpressing transgenic Nile tilapia

Abstract

Several lines of GH-overexpressing fish have been produced and characterized concerning organ integrity, growth, fertility and health but few and contradictory data are available on IGF-I that mediates most effects of GH. Furthermore, nothing is known on IGF-II. Thus, the expression of both IGFs in liver and various extrahepatic sites of adult transgenic (GH-overexpressing) tilapia and age-matched wild-type fish was determined by real-time PCR. Both IGF-I and IGF-II mRNA were found in all organs investigated and were increased in gills, kidney, intestine, heart, testes, skeletal muscle and brain of the transgenics (IGF-I: 1.4-4-fold; IGF-II: 1.7-4.2-fold). Except for liver, brain and testis the increase in IGF-I mRNA was higher than that in IGF-II mRNA. In pituitary, no significant change in IGF-I or IGF-II mRNA was detected. In spleen, however, IGF-I and IGF-II mRNA were both decreased in the transgenics, IGF-I mRNA even by the 19-fold. In agreement, in situ hybridisation revealed a largely reduced number of IGF-I mRNA-containing leukocytes and macrophages when compared to wild-type. These observations may contribute to better understanding the reported impaired health of GH-transgenic fish. Growth enhancement of the transgenics may be due to the increased expression of both IGF-I and IGF-II in extrahepatic sites. It is also reasonable that the markedly enhanced expression of liver IGF-II mRNA that may mimick an early developmental stage is a further reason for increased growth.

Differential regulation of Igf1 and Igf2 mRNA levels in tilapia hepatocytes: effects of insulin and cortisol on GH sensitivity

“…In brown trout, insulin injection increased plasma Igf1 3 h later (Banos et al 1999), even though in coho salmon hepatocytes, insulin did not affect basal igf1 and suppressed GH-stimulated igf1 (Pierce et al 2005), suggesting that indirect stimulatory effects of insulin on liver Igf1 production may exist in salmonids. In this study, GH-stimulated hepatic igf2 mRNA levels to a biologically significantly greater degree than igf1 mRNA levels in vitro and in vivo, consistent with recent results in GH transgenic tilapia (Eppler et al 2010). This suggests that liverderived endocrine Igf2 may play a larger role than liverderived endocrine Igf1 in mediating the growth-stimulating effects of GH in tilapia.…”

“…Glucose positively regulates igf2 gene expression in fetal rat hepatocytes (Goya et al 1999), and in this study, cortisol tended to suppress basal igf2 in vitro. Injection of GH-stimulated igf1 gene expression, consistent with our in vitro results and previous studies (Kajimura et al 2001, Eppler et al 2010. Injection of insulin tended to decrease igf1 gene expression (not statistically detectable), consistent with the slight suppression of basal igf1 gene expression by insulin seen in vitro.…”

“…Recent studies show that teleost fishes including salmonids, sea bream, carp, catfish, eels, rabbitfish, sea bass, and hybrid striped bass, as well as the dogfish, an elasmobranch, differ from mammals in that liver igf2 gene expression and plasma Igf2 levels are stimulated by GH and respond to metabolic status (Shamblott et al 1995, Tse et al 2002, Vong et al 2003a, Peterson et al 2004, Carnevali et al 2005, Gabillard et al 2006, Wilkinson et al 2006, Ayson et al 2007, Terova et al 2007, Gahr et al 2008, Moriyama et al 2008a, b, Picha et al 2008b, Ponce et al 2008, Devlin et al 2009, Peterson & Waldbieser 2009, Eppler et al 2010, Pierce et al 2010. In primary cultured coho salmon hepatocytes, insulin directly increased igf2 mRNA, and strongly increased the response of igf2 mRNA to GH, but suppressed the response of igf1 mRNA to GH (Pierce et al 2005(Pierce et al , 2010.…”

Growth hormone (GH) treatment acts on the endocrine and autocrine/paracrine GH/IGF-axis and on TNF-α expression in bony fish pituitary and immune organs

“…Furthermore, GH stimulated respiratory burst in vibriosis-furunculosis-vaccinated rainbow trout [28] and plasma lysozyme activity in rainbow trout and channel catfish [29,30]. The stimulatory effects of GH on fish immune functions may be mediated via IGF-I as indicated by the presence of IGF-I gene and peptide in immune tissues [22,31e35], where in tilapia, it has been localised to interrenal cells of the head kidney [31] and to head kidney and spleen leukocytes [22,35].…”

Activation of GH signaling and GH-independent stimulation of growth in zebrafish by introduction of a constitutively activated GHR construct

“…In contrast, overexpression of DC-GHR efficiently attenuated the GHSA activity of GH overexpression, as shown by a lower expression level of igf1 (1.5-fold) than the overexpression of GH alone (3.1-fold). These results clearly indicate the importance of GHR level in GH signaling, and by implication, fish growth, since Igf1 is one of the major effectors of growth performance (Eppler et al 2010).…”