Molecular cloning and gene expression of the gonadotropin-releasing hormone receptor in the orange-spotted grouper, Epinephelus coioides

Identification and Expression Profile of the Gonadotropin-Releasing Hormone Receptor in Common Chinese Cuttlefish, Sepiella japonica

Gonadotropin-releasing hormone (GnRH) plays a vital role in the regulation of reproduction through interaction with a specific receptor (the GnRH receptor). In this study, the GnRH receptor gene from the cuttlefish Sepiella japonica (SjGnRHR) was identified and characterized. The cloned full-length SjGnRHR cDNA was 1,468 bp long and contained a 1,029 bp open reading frame encoding 342 amino acid residues, 8 bp of 5' untranslated regions (UTR), and 431 bp of 3' UTR. The putative protein was predicted to have a molecular weight of 38.75 kDa and an isoelectric point of 9.47. In addition, this protein was identified as belonging to the rhodopsin-type (class A) G protein-coupled receptor family. The predicted amino acid sequence contained two N-linked glycosylation sites and 18 phosphorylation sites. Multiple sequence alignment, phylogenetic tree analysis, and three-dimensional structure modeling were conducted to clarify SjGnRHR bioinformatics characteristics. In vitro SjGnRHR expression was carried out using HEK293 cells and the pEGFP-N1 plasmid, to verify the transmembrane properties of this protein. The interaction between the S. japonica GnRH receptor and its ligand was clarified using internalization analysis. SjGnRHR transcriptional quantification confirmed the wide distribution of SjGnRHR in various S. japonica mature tissues. In addition, the transcriptional profile of SjGnRHR in the female brain and ovary during gonadal development was analyzed. Results indicate that GnRHR may be involved in diverse S. japonica physiological functions, especially in the control of reproduction.

Molecular characterization of three GnRH receptor paralogs in the European eel, Anguilla anguilla: tissue-distribution and changes in transcript abundance during artificially induced sexual development

Gonadotropin-releasing hormone receptor (GnRH-R) activation stimulates synthesis and release of gonadotropins in the vertebrate pituitary and also mediates other processes both in the brain and in peripheral tissues. To better understand the differential function of multiple GnRH-R paralogs, three GnRH-R genes (gnrhr1a, 1b, and 2) were isolated and characterized in the European eel. All three gnrhr genes were expressed in the brain and pituitary of pre-pubertal eels, and also in several peripheral tissues, notably gills and kidneys. During hormonally induced sexual maturation, pituitary expression of gnrhr1a (female) and gnrhr2 (male and female) was up-regulated in parallel with gonad development. In the brain, a clear regulation during maturation was seen only for gnrhr2 in the midbrain, with highest levels recorded during early vitellogenesis. These data suggest that GnRH-R2 is the likely hypophysiotropic GnRH-R in male eel, while both GnRH-R1a and GnRH-R2 seems to play this role in female eels.

Regulation of two forms of gonadotropin-releasing hormone receptor gene expression in the protandrous black porgy fish, Acanthopagrus schlegeli

Two GnRH receptors (GnRH-R I and GnRH-R II) were obtained in protandrous black porgy (Acanthopagrus schlegeli). We investigated their tissue distribution, developmental/seasonal changes and regulation of expression using in vivo and in vitro (primary cultures of dispersed pituitary cells) approaches. The relative expressions of GnRH-Rs in the pituitary and gonad were as follows: pituitary: GnRH-R I > GnRH-R II; testicular tissue: GnRH-R I > GnRH-R II; ovarian tissue: GnRH-R I = GnRH-R II. GnRH-R I but not GnRH-R II expression was higher in the pituitary during the spawning period as compared to the prespawning. The expression profiles of both forms of GnRH-R were variable in the gonads according to the gonadal stage and season. In vivo, hCG stimulated GnRH-R I and GnRH-R II expression in testis and ovary. The LHRH analog also up-regulated both receptors in testis and but increased only GnRH-R II in the ovary. Sex steroids (estradiol, E2 and testosterone, T) increased the expression of both receptors in the testis and ovary. In the pituitary, sex steroids (E2 and T) increased the expression of GnRH-R I, but not GnRH-II, both in vivo and in vitro. The LHRH analog also specifically up-regulated the expression of GnRH-R I, but not GnRH-R II, by pituitary cells in vitro. All these data suggest that GnRH-R I rather than GnRH-R II may play a major physiological role in the pituitary. In contrast, both GnRH-R I and GnRH-R II may participate in the regulation of gonadal functions, including a possible role during sex change.

Molecular mechanisms underlying sex change in hermaphroditic groupers

Groupers are widely distributed throughout the tropical and subtropical waters of the world and are regarded as a favourite marine food fish. However, their large-scale aquaculture has been hindered by the rarity of natural males. Being protogynous hermaphrodites, groupers have been considered as study model for development and reproduction, especially for sex determination or sex differentiation, owing to the advantage that grouper gonad development undergoes transition from ovary to intersexual gonad and then to testis, and primordial germ cells and different stages of gametic cells during oogenesis and spermatogenesis are synchronously observed in the transitional gonads. Recently, a series of genes related to the reproduction regulation or sex differentiation have been identified in the groupers, mainly by researchers in China. One important finding was that the grouper gene, doublesex/male abnormal 3-related transcription factor 1 (DMRT1), is not only differentially expressed in gonads at different stages, but that it is also restricted to specific stages and specific cells of spermatogenesis. Grouper DMRT1 protein exists only in spermatogonia, primary spermatocytes and secondary spermatocytes, but not in the supporting Sertoli cells. Moreover, no introns were found in the grouper DMRT1, and no duplicated DMRT1 genes were detected. The finding implies that the intronless DMRT1 that is able to undergo rapid transcriptional turnover might be a significant gene for stimulating spermatogenesis in the protogynous hermaphroditic gonad. Additionally, we have found that grouper expression of sex-determining region Y-related high-mobility group-box gene 3 (SOX3) is a significant time point for enterable gametogenesis of primordial germ cells, because SOX3 is obviously expressed and localized in primordial germ cells. As SOX3 continues to express, the SOX3-positive primordial germ cells develop toward oogonia and then oocytes, whereas, when SOX3 expression is ceased, the SOX3-positive primordial germ cells develop toward spermatogonia. Therefore, we suggest that SOX3, as a transcription factor, might have more important roles in oogenesis than in spermatogenesis. Based on the findings, a hypothetic molecular mechanism underlying sex change is proposed in the hermaphroditic groupers, and some candidate genes related to the grouper sex change are also suggested for further research.