Characterization, Localization, and Stage-Dependent Gene Expression of Gonadotropin Receptors in Chub Mackerel (Scomber japonicus) Ovarian Follicles

Abstract

The pituitary gonadotropins (GtHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are key regulators of gametogenesis in teleosts. However, little is known about the physiological mechanisms by which GtHs regulate asynchronous oocyte development in multiple-spawning marine fishes. We cloned cDNAs encoding GtH receptors (FSHR and LHR) from chub mackerel (Scomber japonicus). FSH and LH were purified by anion-exchange chromatography, gel filtration, and concanavalinA-agarose. When expressed in mammalian cells, FSHR and LHR responded strongly to their own ligands. By separating LH into two subunits by the use of reverse-phase chromatography, we found that the beta-subunit is responsible for signal transduction and the alpha-subunit may be important for holding hormone-receptor complex. In situ hybridization showed that only fshr was expressed in prefollicle and granulosa cells in oocytes at the perinucleolus and cortical alveolus stages, suggesting that FSH is involved in the primary and early secondary growth of oocytes. In ovarian follicles during vitellogenesis, both fshr and lhr were expressed in granulosa and thecal cells, and lhr was strongly expressed during germinal vesicle migration (GVM). Real-time PCR analysis of stage-dependent fshr and lhr expression showed that fshr expression was high in ovarian follicles throughout vitellogenesis and decreased during GVM, whereas lhr expression was low in early vitellogenesis, but increased markedly in the late phase of vitellogenesis, remaining high during GVM. These findings suggest that switching of the expression of FSHR to LHR controls the effects of FSH and/or LH on vitellogenesis and final oocyte maturation via steroid production in granulosa and thecal cells.

Regulation of sex steroid production and mRNAs encoding gonadotropin receptors and steroidogenic proteins by gonadotropins, cyclic AMP and insulin-like growth factor-I in ovarian follicles of rainbow trout (Oncorhynchus mykiss) at two stages of vitellogenesis

“…Relative changes in gonadotropin receptor abundance have been documented for several teleost species (Kim et al, 2012;Kobayashi et al, 2008;Andersson et al, 2009;Rocha et al, 2009;Garcia-Lopez et al, 2011;Nyuji et al, 2013;Guzmán et al, 2014). No evidence was found in this study for an upregulation of receptor mRNA levels.…”

Gonadotropins in European sea bass: Endocrine roles and biotechnological applications

“…None of the gonadotropins showed cross-receptor binding at any of the concentrations tested, as they were only able to stimulate their cognate receptors. These specific interactions have been found in other fish species, such as tilapia (Aizen et al, 2012), rainbow trout (Sambroni et al, 2007), Manchurian trout (Ko et al, 2007), and chub mackerel (Nyuji et al, 2013); while amago salmon (Oba et al, 1999), Atlantic salmon (Andersson et al, 2009), African catfish (Vischer et al, 2003), Senegalese sole (Chauvigné et al, 2012) and zebrafish (So et al, 2005) have shown promiscuous activation of Fshr by Lh.…”

Molecular and transcriptional characterization of GTHs and mPRα during ovarian maturation in rock bream Oplegnathus fasciatus

“…Salmonids, which spawn once in a lifetime or per year, exhibit synchronous oocyte development. Most commercially cultured marine teleosts are multiple‐spawning fish that exhibit group‐synchronous or asynchronous oocyte development and, thus, have ovaries containing oocytes at various stages of development (Nyuji et al, ). In rock bream, histological analysis of the gonads revealed that the ovary contains clutches of oocytes at several stages of development; thus, the action of both FSH and LH is required for continuous ovarian maturation and ovulation throughout the spawning season.…”