Insulin-like growth factor I (IGF-I) in a growth-enhanced transgenic (GH-overexpressing) bony fish,the tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>): indication for a higher impact of autocrine/paracrine than of endocrine IGF-I |
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Authors: | Elisabeth Eppler Antje Caelers Natallia Shved Guylin Hwang Azizur M Rahman Norman Maclean Jürgen Zapf Manfred Reinecke |
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Institution: | (1) Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Winterthurerstr 190, 8057 Zürich, Switzerland;(2) School of Biological Sciences, University of Southampton, Southampton, Hampshire, SO16 7PX, UK |
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Abstract: | 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/μg 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/μg 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. |
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Keywords: | IGF-I IGFBP Liver Serum Skeletal muscle Transgenic fish |
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