Temporal expression of G-protein-coupled receptor 54 (GPR54), gonadotropin-releasing hormones (GnRH), and dopamine receptor D2 (drd2) in pubertal female grey mullet, Mugil cephalus.
ABSTRACT The G-protein-coupled receptor 54 (muGPR54) cDNA was cloned from the brain of the grey mullet, and its expression level, as well as those of the gonadotropin-releasing hormones (GnRH1, GnRH2, GnRH3) and dopamine receptor D2 (drd2), in the brain, pituitary and ovary of pubertal fish (early, intermediate, advanced) were determined by real-time quantitative RT-PCR (QPCR). The muGPR54 cDNA has an open reading frame of 1140 bp with a predicted 380 amino acid peptide, containing seven putative transmembrane domains and putative N-glycosylation and protein kinase C phosphorylation sites. QPCR results showed that the early stage of puberty in grey mullet is characterized by significantly high levels of expression of GPR54, GnRH and drd2 in the brain relative to the intermediate and advanced stages, except for GnRH1 that increased at the advanced stage of puberty. In the pituitary, drd2 expression declined significantly at the advanced stage relative to levels at the intermediate stage. Ovarian expression of GPR54 significantly increased from the intermediate stage of puberty relative to the early stage while that of GnRH1 acutely increased at the advanced stage of puberty. The ovarian expression of drd2 decreased as puberty progressed, but the changes were not significant. The results suggest the possible role of GPR54 and GnRH in positively regulating pubertal development in grey mullet and the dopaminergic inhibition of reproductive function mediated by drd2.
- SourceAvailable from: Mitsuo Nyuji[Show abstract] [Hide abstract]
ABSTRACT: The kisspeptin receptor (Kiss1R) is a cognate receptor for kisspeptin (Kiss), and this Kiss-Kiss1R system has been shown to regulate seasonal reproduction in vertebrates. Our previous study found the chub mackerel (Scomber japonicus) brain expresses both kiss1 and kiss2 and exhibits sexually dimorphic changes during the seasonal reproductive cycle. The present study cloned two subtypes of kissr from the chub mackerel brain, and their signal transduction pathways to Kiss1 and Kiss2 were characterized in a mammalian cell line. Results of identification showed that kissr1 and kissr2 mRNAs encode 369 and 378 deduced amino acids, respectively, and share 52% similarity in amino acid sequences. In vitro functional analysis revealed that chub mackerel Kiss receptor signals are also preferentially transduced via the protein kinase C (PKC) rather than protein kinase A (PKA) pathway. Synthetic chub mackerel Kiss1-15 and Kiss2-12 peptides showed the highest potency for the activation of KissR1 and KissR2, respectively, stronger than their corresponding Kiss-10 peptides. Tissue distribution analyses indicated that both genes are highly expressed in the brain and that only kissr2 mRNA is expressed in the pituitary of both sexes. Unexpectedly, both kissr1 and kissr2 mRNAs were detected only in the testes. Seasonal expression changes showed higher expression levels of both kissr1 and kissr2 mRNAs in the brain of females during the early vitellogenic period; however, no significant differences were found in the brain of males. Pituitary kissr2 mRNA levels showed no significant variations. In the testes, the kissr1 mRNA expression level increased dramatically at spermiation compared with the immature and post-spawning periods. However, kissr2 mRNA levels in the testes did not vary significantly at different testicular stages. These results suggest that both kissr1 and kissr2 likely participate in the seasonal ovarian development of females, and thus in males, we propose a paracrine or autocrine role for kissr1 in testicular development.General and Comparative Endocrinology 08/2013; · 2.82 Impact Factor
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ABSTRACT: Kisspeptin regulates reproductive events, including puberty and ovulation, primarily via GnRH neurons. Prolonged treatment of pre-pubertal striped bass females with Kiss1 or Kiss2 peptides failed to enhance puberty but suggested a gnrh-independent pituitary control pathway. Kiss2 inhibited, but Kiss1 stimulated FShβ expression and gonadal development, although hypophysiotropic gnrh1 and gnrh receptor expression remained unchanged. In situ hybridization and immunohistochemistry on brains and pituitaries revealed a differential plasticity between the two kisspeptin neurons. The differences were most pronounced at the pre-spawning phase in two regions along the path of gnrh1 axons: the nucleus lateralis tuberis (NLT) and the neurohypophysis. Kiss1 neurons appeared in the NLT and innervated the neurohypophysis of pre-spawning males and females, reaching Lh gonadotropes in the proximal pars distalis. Males, at all reproductive stages, had Kiss2 innervations in the NLT and the neurohypophysis, forming large axonal bundles in the former and intermingling with gnrh1 axons. Unlike in males, only pre-ovulatory females had massive NLT-neurohypophysis staining of kiss2. Kiss2 neurons showed a distinct appearance in the NLTv-equivalent region only in spawning zebrafish, indicating that this phenomenon is wide-spread. These results underscore the NLT as important nuclei for kisspeptin action in two facets: 1) kisspeptin - gnrh interaction: both kisspeptins are involved in the regulation of gnrh release, in a stage- and sex-dependent manner, especially at the pre-spawning phase and 2) gnrh-independent effect of Kiss peptides on the pituitary, which together with the plastic nature of their neuronal projections to the pituitary, implies that a direct gonadotropic regulation is plausible.Endocrinology 01/2014; · 4.72 Impact Factor
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ABSTRACT: Fish reproduction is regulated by the hypothalamus-pituitary-gonadal (HPG) axis. Within the HPG axis, gonadotropin-releasing hormone (GnRH) has been well recognized as the master molecule of reproduction, which regulates synthesis and release of gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), from the pituitary. In recent years, new molecules such as kisspeptins and gonadotropin-inhibitory hormone (GnIH) in the HPG axis have become the focus of research in reproductive neuroendocrinology. Each of them is considered to play an important role in the control of the HPG axis, in particular in the positive and negative feedback actions. In this chapter, we summarize the old and new molecules in the HPG axis from anatomical and physiological points of view.10/2013: pages 153-182; , ISBN: 978-1-62618-848-8