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Hormonal and cellular regulation and actions of IGF-III in the ovary of zebrafish (Danio rerio)

Irwin, David / A and Van der Kraak, Glen (2012) Hormonal and cellular regulation and actions of IGF-III in the ovary of zebrafish (Danio rerio). General and Comparative Endocrinology, 177 (1). pp. 187-194. ISSN 0016-6480


Insulin-like growth factors (IGF) are known paracrine/autocrine regulators of ovarian development in teleosts. Initial studies investigated the hormonal and intracellular signalling cascades involved in regulating the expression of ovarian-derived IGFs in zebrafish (Danio rerio). Quantitative real-time PCR was used to quantify the expression of igf3, igf2a, and igf2b in full grown immature (FG; 0.57-0.65 mm) and mid-vitellogenic (MV; 0.45-0.56 mm) follicles. Addition of the gonadotropin analogue human chorionic gonadotropin (hCG) and the adenylate cyclase activator forskolin increased igf3 expression in FG and MV follicles, but had no effect on igf2a or igf2b expression. The effects of hCG on igf3 expression were blocked by the addition of the protein kinase A inhibitor H-89. Pituitary adenylate cyclase activating peptide also stimulated a small increase in igf3 expression in FG follicles, while growth hormone and salmon gonadotropin releasing hormone had no effect on igf3, igf2a, or igf2b expression. Secondary studies investigated the involvement of ovarian-derived IGFs in mediating the ovarian actions of gonadotropins on cell survival and steroidogenesis. Treatment of FG follicles with recombinant human IGF-I, hCG, or forskolin inhibited the induction of caspase-3/7 activity, which was used as a measure of apoptosis. The effects of hCG and forskolin on caspase-3/7 were attenuated by co-treatment with NVP-AEW541, an IGF-I receptor antagonist. In other studies, hCG was shown to increase the production of the maturation-inducing steroid 17α, 20β-dihydroxy-4-pregnen-3-one, but this action was not affected by co-treatment with NVP-AEW541. These results suggest there is a high degree of hormonal specificity in regulating IGFs in the zebrafish ovary and the ovarian-derived IGFs, presumably IGF-III, are downstream mediators of gonadotropin-dependent cell survival, but are not involved in gonadotropin-induced steroidogenesis.

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Keywords: Zebrafish, IGF-III, gonadotropins, cAMP/PKA, Caspase-3/7, qPCR
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Date Deposited: 13 Oct 2015 13:14
Last Modified: 13 Oct 2015 13:14