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Novel Expression of Gonadotropin Subunit Genes in Oocytes of the Gilthead Seabream (Sparus aurata)

Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, Maryland 21202

Address all correspondence and requests for reprints to: Yonathan Zohar, Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 East Pratt Street, Baltimore, Maryland 21202. E-mail: zohar{at}umbi.umd.edu.

It is widely believed that FSH and LH, which are known to play key roles in controlling the production of functional oocytes in vertebrates, are synthesized and secreted exclusively by the anterior pituitary. Here we present evidence for the novel expression of FSHß, LHß, and the common glycoprotein- (Cg) in the gilthead seabream ovary. Using in situ hybridization and immunocytochemistry, FSHß was detected in primary-growth and secondary-growth-I oocytes, LHß was found in secondary-growth oocytes, and Cg was observed in both primary and secondary-growth oocytes. Northern blot analyses demonstrated that Fshß transcript is 0.6 kb in both pituitary and ovary, whereas the ovarian Lhß transcript (1.1 kb), unexpectedly, is longer than the known pituitary Lhß transcript (0.6 kb). Sequence analyses revealed that ovarian Lhß is driven by a different promoter than pituitary Lhß, which generates an additional 459 bases at the distal portion of the 5'-untranslated region of the ovarian Lhß. Furthermore, using in vitro ovarian fragment incubation, we demonstrated that mammalian GnRH analog agonist enhanced the expression of ovarian Fshß (up to 2.7-fold), Lhß (up to 1.4-fold), Cg (up to 1.8-fold), and the secretion of ovarian LH (up to 2.2-fold). In contrast, GnRH antagonist, analog E, suppressed the secretion of ovarian LH. Our findings suggest that a GnRH-gonadotropin axis is present in the gilthead seabream ovary and that FSH and LH, the well-characterized pituitary hormones, may have prominent novel roles in teleost intraovarian communication between oocytes and ovarian follicle cells.

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