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Insulin-like growth factor-3 (IGF-3) in male and female gonads of the tilapia: Development and regulation of gene expression by growth hormone (GH) and 17a-ethinylestradiol (EE2)

Berishvili G., Baroiller J.F., Eppler E., Reinecke M.. 2010. General and Comparative Endocrinology, 167 (1) : p. 128-134.

DOI: 10.1016/j.ygcen.2010.01.023

Recently, in addition to IGF-1 and IGF-2 the existence of a third form of IGF, termed IGF-3, limited to fishes, to be present only in the gonads and encoded by a separate gene has been reported. However, no further data have been presented on IGF-3. The present study on tilapia (Oreochromis niloticus) uses quantitative real-time PCR specific for tilapia IGF-1 and IGF-3. The organ distribution of IGF-3 mRNA in adult fish and the early ontogeny of IGF-3 in male and female gonads were studied. The potential sensitivity of IGF-3 to GH was revealed by intraperitoneal injections of bream GH using IGF-1 as control gene. The effects of 17a-ethinylestradiol (EE2) exerted after feeding of high EE2 doses and exposure to low environmentally relevant EE2 doses on IGF-3 expression in testis and ovary during early development were determined. Low IGF-3 mRNA expression levels were detected in most organs studied, with the highest extra-gonadal amount in the pituitary. During development, the IGF-3 gene was significantly upregulated in male but downregulated in female gonad. Injections of GH elevated IGF-1 mRNA in male and female liver and ovary. IGF-3 did not respond to GH treatment neither in ovary nor in testis. Both EE2 treatments resulted in significant downregulations of IGF-3 mRNA in testis while ovarian IGF-3 mRNA did not respond. Thus, IGF-3 may be involved in reproduction of fishes most likely in the male gonad only. Whether IGF-3 also has some physiological significance in ovary or other organs should be the topic of further studies.

Mots-clés : oreochromis niloticus; insuline; facteur de croissance; oestrogène; phylogénie; poisson osseux; ovaire; expression des gènes; somatotropine; régulation hormonale; développement biologique; physiologie de la reproduction

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