Sexually Dimorphic Expression of Gonadotropin Subunits in the Pituitary of Protogynous Honeycomb Grouper (Epinephelus merra): Evidence That Follicle-Stimulating Hormone (FSH) Induces Gonadal Sex Change1

Abstract

Recent studies have suggested that the hypothalamic-pituitary-gonadal axis is involved in gonadal sex change in sex-changing teleosts. However, its underlying mechanism remains largely unknown. In this study, we focused on the distinct roles of two gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), in the protogynous hermaphrodite teleost, honeycomb grouper (Epinephelus merra). First, we investigated the expression pattern of mRNAs for GTH subunits (cga, fshb, and lhb) in the pituitaries from fish at the different sexual phases. Real-time RT-PCR analyses showed that fhsb mRNA levels in the female pituitary were low. However, fshb transcripts increased dramatically in association with testis development. In contrast, levels of cga and lhb mRNAs did not significantly vary during sex change. In addition, immunohistochemical observations of Fshb- and Lhb-producing cells in the pituitary, through the use of specific antibodies for detections of teleost GTH subunits, were consistent with sexually dimorphic expression of Fshb. In order to identify the role of GTH in gonad of honeycomb grouper, we treated females with bovine FSH (50 or 500 ng/fish) or LH (500 ng/fish) in vivo. After 3 wk, FSH treatments induced female-to-male sex change and up-regulated endogenous androgen levels and fshb transcripts, whereas LH treatment had no effect on sex change. These results suggest that FSH may trigger the female-to-male sex change in honeycomb grouper.

Bending Genders: The Biology of Natural Sex Change in Fish

“…Manipulating GnRH or GtH signalling can induce partial or complete sex change in protogynous (e.g., honeycomb grouper, Kobayashi et al [2010a]; rainbow wrasse, Reinboth and Bnrusle-Sicard [1997]) and protan- [Lee et al, 2001]. Expression of GtH subunits and their receptors (LHR, FSHR) also fluctuates across sex change in protogynous [e.g., Kobayashi et al, 2010a], protandrous [e.g., An et al, 2009An et al, , 2010, and bidirectional [e.g., Kobayashi et al, 2009] species.…”

“…Expression of GtH subunits and their receptors (LHR, FSHR) also fluctuates across sex change in protogynous [e.g., Kobayashi et al, 2010a], protandrous [e.g., An et al, 2009An et al, , 2010, and bidirectional [e.g., Kobayashi et al, 2009] species. However, the precise roles of GnRH and GtH signalling in controlling sex change is difficult to model as patterns are inconsistent even between closely related species, e.g., contradictory patterns of expression for GtH receptors are observed in protogynous grouper [Alam et al, 2010;Hu et al, 2011] and may reflect species-specific gonadotropin functioning in teleosts [Levavi-Sivan et al, 2010].…”

Cortisol Administration Induces Sex Change from Ovary to Testis in the Protogynous Wrasse, <b><i>Halichoeres trimaculatus</i></b>

“…mone, which is one of the gonadotropins controlling the secretion of sex steroid hormones, has been reported to be a trigger for sex change in a protogynous grouper [Kobayashi et al, 2010a]. Thus, shifts in steroidogenesis might play physiologically conclusive roles during sex change.…”

Molecular cloning of GnRH1 gene and GTH cDNAs of the protogynous longtooth grouper, Epinephelus bruneus

“…As the longtooth grouper reverses its functional sex, and GTHs are key molecules in the endocrine system concerning reproduction, these mechanisms are of great interest. Recently, in a study of GTH subunits in honeycomb grouper, FSH was reported to trigger the female-to-male sex change (Kobayashi et al, 2010). Thus, further research into its regulatory mechanism and relationship with other molecules is required.…”