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Marvel M, Levavi-Sivan B, Wong TT, Zmora N, Zohar Y. Gnrh2 maintains reproduction in fasting zebrafish through dynamic neuronal projection changes and regulation of gonadotropin synthesis, oogenesis, and reproductive behaviors. Sci Rep 2021; 11:6657. [PMID: 33758252 PMCID: PMC7987954 DOI: 10.1038/s41598-021-86018-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 01/29/2021] [Indexed: 01/31/2023] Open
Abstract
Restricted food intake, either from lack of food sources or endogenous fasting, during reproductive periods is a widespread phenomenon across the animal kingdom. Considering previous studies show the canonical upstream regulator of reproduction in vertebrates, the hypothalamic Gonadotropin-releasing hormone (Gnrh), is inhibited in some fasting animals, we sought to understand the neuroendocrine control of reproduction in fasted states. Here, we explore the roles of the midbrain neuropeptide, Gnrh2, in inducing reproduction via its pituitary prevalence, gonadotropin synthesis, gametogenesis, and reproductive outputs in the zebrafish model undergoing different feeding regimes. We discovered a fasting-induced four-fold increase in length and abundance of Gnrh2 neuronal projections to the pituitary and in close proximity to gonadotropes, whereas the hypothalamic Gnrh3 neurons are reduced by six-fold in length. Subsequently, we analyzed the functional roles of Gnrh2 by comparing reproductive parameters of a Gnrh2-depleted model, gnrh2-/-, to wild-type zebrafish undergoing different feeding conditions. We found that Gnrh2 depletion in fasted states compromises spawning success, with associated decreases in gonadotropin production, oogenesis, fecundity, and male courting behavior. Gnrh2 neurons do not compensate in other circumstances by which Gnrh3 is depleted, such as in gnrh3-/- zebrafish, implying that Gnrh2 acts to induce reproduction specifically in fasted zebrafish.
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Affiliation(s)
- Miranda Marvel
- grid.266673.00000 0001 2177 1144Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD 21202 USA
| | - Berta Levavi-Sivan
- grid.9619.70000 0004 1937 0538Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food, and Environment, The Hebrew University of Jerusalem, 76100 Rehovot, Israel
| | - Ten-Tsao Wong
- grid.266673.00000 0001 2177 1144Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD 21202 USA
| | - Nilli Zmora
- grid.266673.00000 0001 2177 1144Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD 21202 USA
| | - Yonathan Zohar
- grid.266673.00000 0001 2177 1144Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD 21202 USA
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Muñoz-Cueto JA, Zmora N, Paullada-Salmerón JA, Marvel M, Mañanos E, Zohar Y. The gonadotropin-releasing hormones: Lessons from fish. Gen Comp Endocrinol 2020; 291:113422. [PMID: 32032603 DOI: 10.1016/j.ygcen.2020.113422] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 02/02/2020] [Accepted: 02/03/2020] [Indexed: 12/26/2022]
Abstract
Fish have been of paramount importance to our understanding of vertebrate comparative neuroendocrinology and the mechanisms underlying the physiology and evolution of gonadotropin-releasing hormones (GnRH) and their genes. This review integrates past and recent knowledge on the Gnrh system in the fish model. Multiple Gnrh isoforms (two or three forms) are present in all teleosts, as well as multiple Gnrh receptors (up to five types), which differ in neuroanatomical localization, pattern of projections, ontogeny and functions. The role of the different Gnrh forms in reproduction seems to also differ in teleost models possessing two versus three Gnrh forms, Gnrh3 being the main hypophysiotropic hormone in the former and Gnrh1 in the latter. Functions of the non-hypothalamic Gnrh isoforms are still unclear, although under suboptimal physiological conditions (e.g. fasting), Gnrh2 may increase in the pituitary to ensure the integrity of reproduction under these conditions. Recent developments in transgenesis and mutagenesis in fish models have permitted the generation of fish lines expressing fluorophores in Gnrh neurons and to elucidate the dynamics of the elaborate innervations of the different neuronal populations, thus enabling a more accurate delineation of their reproductive roles and regulations. Moreover, in combination with neuronal electrophysiology, these lines have clarified the Gnrh mode of actions in modulating Lh and Fsh activities. While loss of function and genome editing studies had the premise to elucidate the exact roles of the multiple Gnrhs in reproduction and other processes, they have instead evoked an ongoing debate about these roles and opened new avenues of research that will no doubt lead to new discoveries regarding the not-yet-fully-understood Gnrh system.
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Affiliation(s)
- José A Muñoz-Cueto
- Department of Biology, Faculty of Marine and Environmental Sciences and INMAR, University of Cádiz, CEIMAR, The European University of the Seas (SEA-EU), Puerto Real (Cádiz), Spain.
| | - Nilli Zmora
- Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD, USA
| | - José A Paullada-Salmerón
- Department of Biology, Faculty of Marine and Environmental Sciences and INMAR, University of Cádiz, CEIMAR, The European University of the Seas (SEA-EU), Puerto Real (Cádiz), Spain
| | - Miranda Marvel
- Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD, USA
| | - Evaristo Mañanos
- Institute of Aquaculture of Torre de la Sal, CSIC, Castellón, Spain
| | - Yonathan Zohar
- Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, MD, USA.
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Zmora N, Wong TT, Stubblefield J, Levavi-Sivan B, Zohar Y. Neurokinin B regulates reproduction via inhibition of kisspeptin in a teleost, the striped bass. J Endocrinol 2017; 233:159-174. [PMID: 28330973 DOI: 10.1530/joe-16-0575] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/11/2017] [Accepted: 02/20/2017] [Indexed: 12/14/2022]
Abstract
Kisspeptin and neurokinin B (NKB) are neuropeptides co-expressed in the mammalian hypothalamus and coordinately control GnRH signaling. We have found that Nkb and kisspeptin neurons are distinct in the teleost, striped bass (STB) and capitalized on this phenomenon to study the mode of action of Nkb and its related neuropeptide-F (Nkf), both of which are encoded by the tac3 gene. In vitro brain slices and in vivo administration studies revealed that Nkb/f consistently downregulated kiss2, whereas antagonist (AntD) administration restored this effect. Overall, a minor effect was noted on gnrh1 expression, whereas Gnrh1 content in the pituitaries was reduced after Nkb/f treatment and increased with AntD. Concomitantly, immunostaining demonstrated that hypothalamic Nkb neurons border and densely innervate the largest kiss2 neuronal population in the hypothalamus, which also coexpresses Nkb receptor. No expression of Nkb receptor or Nkb neuronal projections was detected near/in Gnrh1 soma in the preoptic area. At the level of the pituitary, however, the picture was more complex: both Nkb/f and AntD upregulated lhb and fshb expression and Lh secretion in vivo Together with the stimulatory effect of Nkb/f on Lh/Fsh secretion from pituitary cells, in vitro, this may indicate an additional independent action of Nkb/f within the pituitary, in which the hypothalamic pathway is more dominant. The current study demonstrates that Nkb/f utilizes multiple pathways to regulate reproduction in the STB and that in the brain, Nkb mainly acts as a negative modulator of kiss2 to regulate the release of Gnrh1.
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Affiliation(s)
- Nilli Zmora
- Department of Marine BiotechnologyInstitute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
| | - Ten-Tsao Wong
- Department of Marine BiotechnologyInstitute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
| | - John Stubblefield
- Department of Marine BiotechnologyInstitute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
| | - Berta Levavi-Sivan
- Department of Animal SciencesFaculty of Agriculture, Food and Environment, The Hebrew University, Rehobot, Israel
| | - Yonathan Zohar
- Department of Marine BiotechnologyInstitute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
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Zmora N, Stubblefield JD, Wong TT, Levavi-Sivan B, Millar RP, Zohar Y. Kisspeptin Antagonists Reveal Kisspeptin 1 and Kisspeptin 2 Differential Regulation of Reproduction in the Teleost, Morone saxatilis. Biol Reprod 2015; 93:76. [PMID: 26246220 DOI: 10.1095/biolreprod.115.131870] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 08/03/2015] [Indexed: 11/01/2022] Open
Abstract
The importance of kisspeptin in regulating vertebrate reproduction has been well established, but the exact mechanism continues to unfold. Unlike mammals, many lower vertebrates possess a dual kisspeptin system, Kiss1 and Kiss2. To decipher the roles of the kisspeptins in fish, we identified two potential kisspeptin antagonists, pep 234 and pep 359, by screening analogs for their ability to inactivate striped bass Kiss1 and Kiss2 receptors expressed in COS7 cells. Pep 234 (a mammalian KISS1 antagonist) antagonizes Kiss1r signaling activated by Kiss1 and Kiss2, and pep 359 (a novel analog) antagonizes Kiss2 activation of both receptors. In vitro studies using brain slices demonstrated that only Kiss2 can upregulate the expression of the hypophysiotropic gnrh1, which was subsequently diminished by pep 234 and pep 359. In primary pituitary cell cultures, the two antagonists revealed a complex network of putative endogenous and exogenous regulation by kisspeptin. While both kisspeptins stimulate Fsh expression and secretion, Kiss2 predominately induces Lh secretion. Pep 234 and 359 treatment of spawning males hindered sperm production. This effect was accompanied with decreased brain gnrh1 and gnrh2 mRNA levels and peptide content in the pituitary, and increased levels of pituitary Lh, probably due to attenuation of Lh release. Strikingly, the mRNA levels of arginine-vasotocin, the neurons of which in the preoptic area coexpress kiss2r, were dramatically reduced by the antagonists. Our results demonstrate differential actions of Kiss1 and Kiss2 systems along the hypothalamic-pituitary axis and interactions with other neuropeptides, and further reinforce the importance of kisspeptin in the execution of spawning.
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Affiliation(s)
- Nilli Zmora
- Insitute of Marine and Environmental Technology, Department of Marine Biotechnology, University of Maryland Baltimore County, Baltimore, Maryland
| | - John David Stubblefield
- Insitute of Marine and Environmental Technology, Department of Marine Biotechnology, University of Maryland Baltimore County, Baltimore, Maryland
| | - Ten-Tsao Wong
- Insitute of Marine and Environmental Technology, Department of Marine Biotechnology, University of Maryland Baltimore County, Baltimore, Maryland
| | - Berta Levavi-Sivan
- Department of Animal Sciences, Faculty of Agriculture, Food and Environment, the Hebrew University, Rehobot, Israel
| | - Robert Peter Millar
- Mammal Research Institute, Department of Zoology, University of Pretoria, Pretoria, South Africa University of Cape Town/Medical Research Council Receptor Biology Unit, Institute for Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - Yonathan Zohar
- Insitute of Marine and Environmental Technology, Department of Marine Biotechnology, University of Maryland Baltimore County, Baltimore, Maryland
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Hildahl J, Sandvik GK, Edvardsen RB, Fagernes C, Norberg B, Haug TM, Weltzien FA. Identification and gene expression analysis of three GnRH genes in female Atlantic cod during puberty provides insight into GnRH variant gene loss in fish. Gen Comp Endocrinol 2011; 172:458-67. [PMID: 21521645 DOI: 10.1016/j.ygcen.2011.04.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Revised: 04/06/2011] [Accepted: 04/08/2011] [Indexed: 10/18/2022]
Abstract
Gonadotropin releasing hormone (GnRH) is a key regulator of sexual development and reproduction in vertebrates. Fish have either two or three pre-pro-GnRH genes, encoding structurally distinct peptides. We identified three pre-pro-GnRH genes in Atlantic cod (Gadus morhua, gmGnRH) using RT-PCR, RACE-PCR and BAC DNA library clone sequencing based on synteny searching. Gene identity was confirmed by sequence alignment and subsequent phylogenetic analysis. The expression of these genes was measured by quantitative PCR in the brain and pituitary of female cod throughout their reproductive cycle and in peripheral tissues. All three gmGnRH genes have highly conserved deduced decapeptide sequences, but sequence and phylogenetic data for gmGnRH1 suggest that this is a pseudogene. gmGnRH1 shares low identity with all fish GnRH variants and grouped with the GnRH3 clade. Although gmGnRH1 is a putative pseudogene, it is transcribed in multiple tissues but at low levels in the brain, indicating the loss of conserved hypophysiotrophic function. Phylogenetic analysis reveals that gmGnRH2 and gmGnRH3 variants are located in variant-specific clades. Both gmGnRH2 and gmGnRH3 transcripts are most abundant in the brain, with lower expression in pituitaries and ovaries. Brain gmGnRH3 gene expression increases in spawning fish and is expressed in the pituitary during puberty. Brain gmGnRH2 transcripts are highly expressed relative to gmGnRH3 before and during spawning. Sequence and expression data suggest that gmGnRH1 is a pseudogene and that gmGnRH3 is likely the hypophysiotrophic form of GnRH in Atlantic cod.
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Affiliation(s)
- Jon Hildahl
- Norwegian School of Veterinary Science, Department of Basic Sciences and Aquatic Medicine, Oslo, Norway.
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Servili A, Lethimonier C, Lareyre JJ, López-Olmeda JF, Sánchez-Vázquez FJ, Kah O, Muñoz-Cueto JA. The Highly conserved gonadotropin-releasing hormone-2 form acts as a melatonin-releasing factor in the pineal of a teleost fish, the european sea bass Dicentrarchus labrax. Endocrinology 2010; 151:2265-75. [PMID: 20215565 DOI: 10.1210/en.2009-1207] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
With the exception of modern mammals, most vertebrate species possess two GnRH genes, GnRH-1 and GnRH-2. In addition, in many teleost fish, there is a third gene called GnRH-3. If the main function of GnRH-1 is unambiguously to stimulate gonadotropin release, the other two GnRH forms still lack clear functions. This is particularly true for the highly conserved GnRH-2 that encodes chicken GnRH-II. This GnRH variant is consistently expressed in neurons of the dorsal synencephalon in most vertebrate groups but still has no clear functions supported by anatomical, pharmacological, and physiological data. In this study performed on a perciform fish, the European sea bass, we show for the first time that the pineal organ receives GnRH-2-immunoreactive fibers originating from the synencephalic GnRH-2 neurons. This was shown through a combination of retrograde tracing and immunohistochemistry, using highly specific antibodies. Supporting the presence of GnRH-2 functional targets, RT-PCR data together with the in situ hybridization studies showed that the sea bass pineal gland strongly expressed a GnRH receptor (dlGnRHR-II-2b) with clear selectivity for GnRH-2 and, to a lesser extent, the dlGnRHR-II-1a subtype. Finally, in vitro and in vivo experiments demonstrate stimulatory effects of GnRH-2 on nocturnal melatonin secretion by the sea bass pineal organ. Altogether, these data provide, for the first time in a vertebrate species, converging evidence supporting a role of GnRH-2 in the modulation of fish pineal functions.
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Affiliation(s)
- Arianna Servili
- Departamento de Biología, Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Puerto Real, Spain
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Levavi-Sivan B, Avitan A. Sequence analysis, endocrine regulation, and signal transduction of GnRH receptors in teleost fish. Gen Comp Endocrinol 2005; 142:67-73. [PMID: 15862550 DOI: 10.1016/j.ygcen.2005.01.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Revised: 01/16/2005] [Accepted: 01/31/2005] [Indexed: 11/29/2022]
Abstract
Three gonadotropin-releasing hormones (GnRHs) and three cognate receptors have been identified in vertebrates, with distinct distributions and functions. According to their sequences, the receptors can be grouped into distinct classes: types I, II, and III. One branch contains all type-I GnRH receptors (GnRH-R-I) from mammals and fish; another branch clusters mainly amphibian and human type-II GnRH receptors; and a third branch includes evolved fish, mainly perciform species, type-III GnRH receptors. Taken tilapia GnRH receptors as a model, the present study summarizes the information regarding the amino-acid residues assumed to be involved in the receptors' structure, binding, activation, and intracellular signal transduction, including arrangement of the disulfide bonds, glycosylation sites, coupling to G proteins, and protein kinase A or protein kinase C phosphorylation sites.
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Affiliation(s)
- Berta Levavi-Sivan
- Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
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