Novel expression of gonadotropin subunit genes in oocytes of the gilthead seabream (Sparus aurata).

Abstract

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 FSHbeta, LHbeta, and the common glycoprotein-alpha (Cgalpha) in the gilthead seabream ovary. Using in situ hybridization and immunocytochemistry, FSHbeta was detected in primary-growth and secondary-growth-I oocytes, LHbeta was found in secondary-growth oocytes, and Cgalpha was observed in both primary and secondary-growth oocytes. Northern blot analyses demonstrated that Fshbeta transcript is 0.6 kb in both pituitary and ovary, whereas the ovarian Lhbeta transcript (1.1 kb), unexpectedly, is longer than the known pituitary Lhbeta transcript (0.6 kb). Sequence analyses revealed that ovarian Lhbeta is driven by a different promoter than pituitary Lhbeta, which generates an additional 459 bases at the distal portion of the 5'-untranslated region of the ovarian Lhbeta. Furthermore, using in vitro ovarian fragment incubation, we demonstrated that mammalian GnRH analog agonist enhanced the expression of ovarian Fshbeta (up to 2.7-fold), Lhbeta (up to 1.4-fold), Cgalpha (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.