Insulin-like growth factor I (IGF-I) in a growth-enhanced transgenic (GH-overexpressing) bony fish, the tilapia (Oreochromis niloticus): indication for a higher impact of autocrine/paracrine than of endocrine IGF-I.
Several lines of growth hormone (GH)-overexpressing fish have been produced and analysed for growth and fertility parameters. However, only few data are available on the growth-promoting hormone insulin-like growth factor I (IGF-I) that mediates most effects of GH, and these are contradictory. Using quantitative real-time RT-PCR, radioimmunoassay, in situ hybridization, immunohistochemistry, and radiochromatography we investigated IGF-I and IGF binding proteins (IGFBPs) in an adult (17 months old) transgenic (GH-overexpressing) tilapia (Oreochromis niloticus). The transgenics showed an around 1.5-fold increase in length and an approximately 2.3-fold higher weight than the non-transgenics. Using radioimmunoassay, the serum IGF-I levels were lower (6.22 +/- 0.75 ng/ml) in transgenic than in wild-type (15.01 +/- 1.49 ng/ml) individuals (P = 0.0012). Radioimmunoassayable IGF-I in transgenic liver was 4.2-times higher than in wild-type (16.0 +/- 2.21 vs. 3.83 +/- 0.71 ng/g, P = 0.0017). No hepatocytes in wild-type but numerous hepatocytes in transgenic liver contained IGF-I-immunoreactivity. RT-PCR revealed a 1.4-times higher IGF-I mRNA expression in the liver of the transgenics (10.51 +/- 0.82 vs. 7.3 +/- 0.49 pg/microg total RNA, P = 0.0032). In correspondence, in situ hybridization showed more IGF-I mRNA containing hepatocytes in the transgenics. A twofold elevated IGF-I mRNA expression was determined in the skeletal muscle of transgenics (0.33 +/- 0.02 vs. 0.16 +/- 0.01 pg/microg total RNA, P < 0.0001). Both liver and serum of transgenics showed increased IGF-I binding. The increased IGFBP content in the liver may lead to retention of IGF-I, and/or the release of IGF-I into the circulation may be slower resulting in accumulation of IGF-I in the hepatocytes. Our results indicate that the enhanced growth of the transgenics likely is due to enhanced autocrine/paracrine action of IGF-I in extrahepatic sites, as shown here for skeletal muscle.
Eppler
Elisabeth
E
Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Winterthurerstr 190, Zürich, Switzerland.
Caelers
Antje
A
Shved
Natallia
N
Hwang
Guylin
G
Rahman
Azizur M
AM
Maclean
Norman
N
Zapf
Jürgen
J
Reinecke
Manfred
M
D000818:Animals; D030801:Animals, Genetically Modified / Q000235:genetics*; D019898:Autocrine Communication; D004703:Endocrine System / Q000187:drug effects* / Q000378:metabolism; D013006:Growth Hormone / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D019899:Paracrine Communication; D015347:RNA Probes; D012333:RNA, Messenger; D011863:Radioimmunoassay; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017210:Tilapia / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
D015347:RNA Probes; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone