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Department of Animal Sciences
The Robert H. Smith Faculty
of Agricultural, Food & Environment

The Hebrew University of Jerusalem.

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Publications

2020
Burow, S. ; Mizrahi, N. ; Maugars, G. ; von Krogh, K. ; Nourizadeh-Lillabadi, R. ; Hollander-Cohen, L. ; Shpilman, M. ; Atre, I. ; Weltzien, F. - A. ; Levavi-Sivan, B. Characterization of gonadotropin receptors Fshr and Lhr in Japanese medaka, Oryzias latipes. General and Comparative Endocrinology 2020, 285. Publisher's VersionAbstract
Reproduction in vertebrates is controlled by the brain-pituitary-gonad axis, where the two gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) play vital parts by activating their cognate receptors in the gonads. The main purpose of this work was to study intra- and interspecies ligand promiscuity of teleost gonadotropin receptors, since teleost receptor specificity is unclear, in contrast to mammalian receptors. Receptor activation was investigated by transfecting COS-7 cells with either Fsh receptor (mdFshr, tiFshr) or Lh receptor (mdLhr, tiLhr), and tested for activation by recombinant homologous and heterologous ligands (mdFshβα, mdLhβα, tiFshβα, tiLhβα) from two representative fish orders, Japanese medaka (Oryzias latipes, Beloniformes) and Nile tilapia (Oreochromis niloticus, Cichliformes). Results showed that each gonadotropin preferentially activates its own cognate receptor. Cross-reactivity was detected to some extent as mdFshβα was able to activate the mdLhr, and mdLhβα the mdFshr. Medaka pituitary extract (MPE) stimulated CRE-LUC activity in COS-7 cells expressing mdlhr, but could not stimulate cells expressing mdfshr. Recombinant tiLhβα, tiFshβα and tilapia pituitary extract (TPE) could activate the mdLhr, suggesting cross-species reactivity for mdLhr. Cross-species reactivity was also detected for mdFshr due to activation by tiFshβα, tiLhβα, and TPE, as well as for tiFshr and tiLhr due to stimulation by mdFshβα, mdLhβα, and MPE. Tissue distribution analysis of gene expression revealed that medaka receptors, fshr and lhr, are highly expressed in both ovary and testis. High expression levels were found for lhr also in brain, while fshr was expressed at low levels. Both fshr and lhr mRNA levels increased significantly during testis development. Amino acid sequence alignment and three-dimensional modelling of ligands and receptors highlighted conserved beta sheet domains of both Fsh and Lh between Japanese medaka and Nile tilapia. It also showed a higher structural homology and similarity of transmembrane regions of Lhr between both species, in contrast to Fshr, possibly related to the substitution of the conserved cysteine residue in the transmembrane domain 6 in medaka Fshr with glycine. Taken together, this is the first characterization of medaka Fshr and Lhr using homologous ligands, enabling to better understand teleost hormone-receptor interactions and specificities. The data suggest partial ligand promiscuity and cross-species reactivity between gonadotropins and their receptors in medaka and tilapia. © 2019 The Authors
2019
Mizrahi, N. ; Gilon, C. ; Atre, I. ; Ogawa, S. ; Parhar, I. S. ; Levavi-Sivan, B. Deciphering direct and indirect effects of neurokinin B and GnRH in the brain-pituitary axis of tilapia. Frontiers in Endocrinology 2019, 10. Publisher's VersionAbstract
Neurokinin B (NKB) and its cognate receptor (NK3R) are emerging as important components of the neuroendocrine regulation of reproduction. Unlike mammalian tac3, which encodes only one mature peptide (namely NKB), two mature peptides are predicted for each tac3 gene in fish and frogs. Therefore, it was designated as Neurokinin F (NKF). Hormone analogs with high and long-lasting biological activity are important tools for physiological and biological research; however, the availability of piscine-specific analogs is very limited. Therefore, we have developed specific NKB and NKF analogs based on the structure of the mammalian NKB analog–senktide. These analogs, specifically designed for longer half-lives by methylation of proteolysis sites, exhibited activity equal to those of the native NKB and NKF in short-term signal-transduction assays of tilapia NKB receptors. However, the analogs were found to be able to significantly increase the release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and growth hormone (GH) in tilapia, as fast as 1 h after intraperitoneal (IP) injection. The impact of the analogs on LH and FSH secretion lasted longer compared to the effect of native peptides and salmon GnRH analog (sGnRHa). In addition, we harvested pituitaries 24 h post injection and measured LH, FSH and GH mRNA synthesis. Both analogs elevated mRNA levels of LH and GH, but only NKB analog increased FSH mRNA levels in the pituitary and all GnRH forms in the brain. NKB receptors were co-localized with all three types the GnRH neurons in tilapia brain in situ. We previously showed a direct effect of NKB at the pituitary level, and these new results suggest that the stronger impact of the NKB analog on GTH release is also due to an indirect effect through the activation of GnRH neurons. These results suggest that novel synthetic NKB analogs may serve as a tool for both research and agricultural purposes. Finally, the biological activity and regulatory role of NKB in tilapia brain and pituitary suggest that the NKB/NKBR system in fish is an important reproductive regulator in a similar way to the kisspeptin system in mammals. Copyright © 2019 Mizrahi, Gilon, Atre, Ogawa, Parhar and Levavi-Sivan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Hollander-Cohen, L. ; Böhm, B. ; Hausken, K. ; Levavi-Sivan, B. Ontogeny of the specificity of gonadotropin receptors and gene expression in carp. Endocrine Connections 2019, 8 1433-1446. Publisher's VersionAbstract
The pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are the principle endocrine drivers of reproductive processes in the gonads of jawed vertebrates. Canonically, FSH recruits and maintains selected ovarian follicles for maturation and LH induces the stages of germinal vesicle breakdown and ovulation. In mammals, LH and FSH specifically activate cognate G-protein-coupled receptors that affect the proteins involved in steroidogenesis, protein hormone synthesis, and gametogenesis. This dual-gonadotropin model also exists in some fish species, but not in all. In fact, due to their diverse number of species, extended number of ecological niches, and remarkably flexible reproductive strategies, fish are appropriate as models to understand the co-evolution of gonadotropins and their receptors. In this study, we cloned and characterized the expression profile over the final stages of ovarian maturation of carp (Cyprinus carpio) LHCGR and FSHR. Expression of both gonadotropin receptors increased in the later stage of early vitellogenesis, suggesting that both LH and FSH play a role in the development of mature follicles. We additionally tested the activation of cLHCGR and cFSHR using homologous and heterologous recombinant gonadotropins in order to gain insight into an evolutionary model of permissive gonadotropin receptor function. These data suggest that carp (Cyprinus carpio) gonad development and maturation depends on a specific gonadotropin profile that does not reflect the temporally distinct dual-gonadotropin model observed in salmonids or mammals, and that permissive gonadotropin receptor activation is a specific feature of Ostariophysi, not all teleosts. © 2019 The authors.
Hausken, K. ; Levavi-Sivan, B. Synteny and phylogenetic analysis of paralogous thyrostimulin beta subunits (GpB5) in vertebrates. PLoS ONE 2019, 14. Publisher's VersionAbstract
At some point early in the vertebrate lineage, two whole genome duplication events (1R, 2R) took place that allowed for the diversification and sub-/neo-functionalization of the glycoprotein hormones (GpHs). All jawed vertebrates possess the GpHs luteinizing hormone (LH), follicle stimulating hormone (FSH), and thyroid stimulating hormone (TSH), each of which are heterodimers with a common alpha subunit and unique beta subunits. In 2002, a novel glycoprotein hormone named thyrostimulin was described to have unique GpA2 and GpB5 subunits that were homologous to the vertebrate alpha and beta subunits. The presence of GpA2 and GpB5 in representative protostomes and deuterostomes indicates their ancestry in the GpH family. There are several reports of GpH subunit evolution, but none have included GpA2 and GpB5 for species in each major vertebrate class. Thus, we addressed the ancestry of two paralogous GpB5 subunits (GpB5a and GpB5b) that were previously only recognized in two teleost species. Our search for orthologous GpB5a and GpB5b sequences in representative vertebrates and phylogenetic analysis, in addition to the currently published evolutionary scenarios of the GpH family, supports that GpB5a and GpB5b are paralogs that arose from the first vertebrate whole genome duplication event (1R). Syntenic analysis supports lineage specific losses of GpB5a in chondrichthyes, basal actinopterygians, and tetrapods, and retention in coelacanth and teleosts. Additionally, we were unable to identify GpA2 transcripts from tilapia mRNA, suggesting that this species does not produce heterodimeric thyrostimulin. While the conserved or even species-specific functional role of thyrostimulin or its individual subunits are still unknown in vertebrates, the analyses presented here provide context for future studies on the functional divergence of the GpH family. © 2019 Hausken, Levavi-Sivan. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Burow, S. ; Fontaine, R. ; von Krogh, K. ; Mayer, I. ; Nourizadeh-Lillabadi, R. ; Hollander-Cohen, L. ; Cohen, Y. ; Shpilman, M. ; Levavi-Sivan, B. ; Weltzien, F. - A. Establishment of specific enzyme-linked immunosorbent assay (ELISA) for measuring Fsh and Lh levels in medaka (Oryzias latipes), using recombinant gonadotropins. MethodsX 2019, 6 1473 - 1479. Publisher's VersionAbstract
The paucity of information on understanding the regulatory mechanisms that are involved in the control of piscine Fsh and Lh synthesis, secretion, and function, prompted the present work. Part of the problem is related to the molecular heterogeneity and the unavailability of Fsh and Lh assays for quantifying gonadotropins, in particular assays regarding the measurement of Fsh, and such assays are available today for only a few teleost species. The present study reports the development and validation of competitive ELISAs for quantitative determination of medaka Fsh and Lh by first producing medaka recombinant (md) gonadotropins mdFshβ, mdLhβ, mdFshβα, and mdLhβα by Pichia pastoris, generating specific antibodies against their respective β subunits, and their use within the development of ELISAs. The advantages of this protocol include: •The reproducibility of the ELISA demonstrated was relatively high, as shown by reasonably low intra- (Fsh 2.7%, Lh 3%) and interassay CVs (Fsh 5.3%, Lh 5.7%).•The high degree of parallelism between serial dilutions of the recombinant and native pituitary-derived Fsh and Lh, may be a sign of similar structures and immunologically similarity.•Two new competitive ELISAs for the quantification of medaka Fsh and Lh were established for the first time.
Ciani, E. ; Fontaine, R. ; Maugars, G. ; Mizrahi, N. ; Mayer, I. ; Levavi-Sivan, B. ; Weltzien, F. - A. Melatonin receptors in Atlantic salmon stimulate cAMP levels in heterologous cell lines and show season-dependent daily variations in pituitary expression levels. Journal of Pineal Research 2019, e12590. Publisher's VersionAbstract
Abstract The hormone melatonin connects environmental cues, such as photoperiod and temperature, with a number of physiological and behavioural processes, including seasonal reproduction, through binding to their cognate receptors. This study reports the structural, functional and physiological characterization of five high-affinity melatonin receptors (Mtnr1aaα, Mtnr1aa?, Mtnr1ab, Mtnr1al, Mtnr1b) in Atlantic salmon. Phylogenetic analysis clustered salmon melatonin receptors into three monophyletic groups, Mtnr1A, Mtnr1Al and Mtnr1B, but no functional representative of the Mtnr1C group. Contrary to previous studies in vertebrates, pharmacological characterization of four receptors in COS-7, CHO and SH-SY5Y cell lines (Mtnr1Aaα, Mtnr1Aa?, Mtnr1Ab, Mtnr1B) showed induction of intracellular cAMP levels following 2-iodomelatonin or melatonin exposure. No consistent response was measured after N-acetyl-serotonin or serotonin exposure. Melatonin receptor genes were expressed at all levels of the hypothalamo-pituitary-gonad axis, with three genes (mtnr1aa?, mtnr1ab and mtnr1b) detected in the pituitary. Pituitary receptors displayed daily fluctuations in mRNA levels during spring, prior to the onset of gonadal maturation, but not in autumn, strongly implying a direct involvement of melatonin in seasonal processes regulated by the pituitary. To the best of our knowledge, this is the first report of cAMP induction mediated via melatonin receptors in a teleost species.
Burow, S. ; Fontaine, R. ; von Krogh, K. ; Mayer, I. ; Nourizadeh-Lillabadi, R. ; Hollander-Cohen, L. ; Cohen, Y. ; Shpilman, M. ; Levavi-Sivan, B. ; Weltzien, F. - A. Data on Western blot and ELISA analysis of medaka (Oryzias latipes) follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) using recombinant proteins expressed with Pichia pastoris. Data in Brief 2019, 22, 1057 - 1063. Publisher's VersionAbstract
The gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) play essential roles in vertebrate reproduction. This article presents data on molecular weight validation of recombinant medaka (Oryzias latipes) (md) gonadotropins Fshβ (mdFshβ), Lhβ (mdLhβ), Fshβα (mdFshβα), and Lhβα (mdLhβα) generated by Pichia pastoris, as well as data on a validation of produced antibodies against Fshβ and Lhβ by Western blot analysis. Furthermore, the article includes data on Fsh and Lh protein levels in male medaka pituitaries using recombinant mdFshβα and mdLhβα within enzyme-linked immunosorbent assays (ELISAs), in which protein amounts were analyzed related to body weight and age of the fish. This dataset is associated with the research article entitled “Medaka Follicle-stimulating hormone (Fsh) and Luteinizing hormone (Lh): Developmental profiles of pituitary protein and gene expression” (Burow et al., in press).
Burow, S. ; Fontaine, R. ; von Krogh, K. ; Mayer, I. ; Nourizadeh-Lillabadi, R. ; Hollander-Cohen, L. ; Cohen, Y. ; Shpilman, M. ; Levavi-Sivan, B. ; Weltzien, F. - A. Medaka follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh): Developmental profiles of pituitary protein and gene expression levels. General and Comparative Endocrinology 2019, 272, 93 - 108. Publisher's VersionAbstract
The two gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) are of particular importance within the hypothalamic-pituitary-gonadal (HPG) axis of vertebrates. In the current study, we demonstrate the production and validation of Japanese medaka (Oryzias latipes) recombinant (md) gonadotropins Fshβ (mdFshβ), Lhβ (mdLhβ), Fshβα (mdFshβα), and Lhβα (mdLhβα) by Pichia pastoris, the generation of specific rabbit antibodies against their respective β subunits, and their use within the development and validation of competitive enzyme-linked immunosorbent assays (ELISAs) for quantification of medaka Fsh and Lh. mdFsh and mdLh were produced as single-chain polypeptides by linking the α subunit with mdFshβ or mdLhβ mature protein coding sequences to produce a “tethered” polypeptide with the β-chain at the N-terminal and the α-chain at the C-terminal. The specificity of the antibodies raised against mdFshβ and mdLhβ was determined by immunofluorescence (IF) for Fshβ and Lhβ on medaka pituitary tissue, while comparison with fluorescence in situ hybridization (FISH) for fshb and lhb mRNA was used for validation. Competitive ELISAs were developed using antibodies against mdFshβ or mdLhβ, and the tethered proteins mdFshβα or mdLhβα for standard curves. The standard curve for the Fsh ELISA ranged from 97.6 pg/ml to 50 ng/ml, and for the Lh ELISA from 12.21 pg/ml to 6.25 ng/ml. The sensitivity of the assays for Fsh and Lh was 44.7 and 70.8 pg/ml, respectively. A profile of pituitary protein levels of medaka Fsh and Lh comparing juveniles with adults showed significant increase of protein amount from juvenile group (body length from 12 mm to 16.5 mm) to adult group (body length from 21 mm to 26.5 mm) for both hormones in male medaka. Comparing these data to a developmental profile of pituitary mRNA expression of medaka fshb and lhb, the mRNA expression of lhb also increased during male maturation and a linear regression analysis revealed a significant increase of lhb expression with increased body length that proposes a linear model. However, fshb mRNA expression did not change significantly during male development and therefore was not correlated with body length. In summary, we have developed and validated homologous ELISA assays for medaka Fsh and Lh based on proteins produced in P. pastoris, assays that will be used to study the functions and regulations of Fsh and Lh in more detail.
2018
Biran, J. ; Levavi-Sivan, B. Endocrine Control of Reproduction, Fish. In; 2018.
Hausken, K. N. ; Tizon, B. ; Shpilman, M. ; Barton, S. ; Decatur, W. ; Plachetzki, D. ; Kavanaugh, S. ; Ul-Hasan, S. ; Levavi-Sivan, B. ; Sower, S. A. Cloning and characterization of a second lamprey pituitary glycoprotein hormone, thyrostimulin (GpA2/GpB5). General and Comparative Endocrinology 2018, 264, 16 - 27. Publisher's VersionAbstract
A novel heterodimeric glycoprotein hormone (GpH) comprised of alpha (GpA2) and beta (GpB5) subunits was discovered in 2002 and called thyrostimulin for its ability to activate the TSH receptor in mammals, but its central function in vertebrates has not been firmly established. We report here the cloning and expression of lamprey (l)GpB5, and its ability to heterodimerize with lGpA2 to form a functional l-thyrostimulin. The full-length cDNA of lGpB5 encodes 174 amino acids with ten conserved cysteine residues and one glycosylation site that is conserved with other vertebrate GpB5 sequences. Phylogenetic and synteny analyses support that lGpB5 belongs to the vertebrate GpB5 clade. Heterodimerization of lGpB5 and lGpA2 was shown by nickel pull-down of histidine-tagged recombinant subunits. RNA transcripts of lGpB5 were detected in the pituitary of lampreys during both parasitic and adult life stages. Intraperitoneal injection with lGnRH-III (100 μg/kg) increased pituitary lGpA2, lGpB5, and lGpHβ mRNA expression in sexually mature, adult female lampreys. A recombinant l-thyrostimulin produced by expression of a fusion gene in Pichia pastoris activated lamprey GpH receptors I and II as measured by cAMP enzymeimmunoassay. In contrast to jawed vertebrates that have pituitary LH, FSH, and TSH, our data support that lampreys only have two functional pituitary GpHs, lGpH and l-thyrostimulin, which consist of lGpA2 and unique beta subunits. It is hypothesized that lGpH and l-thyrostimulin differentially regulate reproductive and thyroid activities in some unknown way(s) in lampreys.
Hollander-Cohen, L. ; Golan, M. ; Aizen, J. ; Shpilman, M. ; Levavi-Sivan, B. Characterization of carp gonadotropins: Structure, annual profile, and carp and zebrafish pituitary topographic organization. General and Comparative Endocrinology 2018, 264, 28 - 38. Publisher's VersionAbstract
Two gonadotropins, follicle stimulating hormone (FSH) and luteinizing hormone (LH), are important players in the hypothalamic-pituitary-gonadal axis of vertebrates. In the present work, we describe the construction of recombinant (r) common carp (Cyprinus carpio; c) FSH (rcFSH) and LH (rcLH) using the Pichia pastoris system, the generation of specific antibodies against their respective β subunits, and their use in the development and validation of specific ELISAs. We produced carp rLH and rFSH as single-chain polypeptides, wherein the GTH subunit α was joined with either cLHβ or cFSHβ mature protein-coding sequences to form a fusion gene that encodes a yoked polypeptide, in which the GTH β-subunit forms the N-terminal part and the α-subunit forms the C-terminal part. Competitive ELISAs were developed, using primary antibodies against rcLHβ or rcFSHβ, respectively, and rcLHβα or rcFSHβα for the standard curves. The standard curves for cLH paralleled those of pituitary extracts of the homologous fish and also those of other cyprinids species like the black carp (Mylopharyngodon piceus), goldfish (Carassius auratus), silver carp (Hypophthalmichthys molitrix), and grass carp (Ctenopharyngodon idella). We used the specific antibodies raised against cFSH and cLH to study the specific localization of the different GTH cells in the pituitary of carp and its taxonomic relative species – the zebrafish. Both FSH and LH cells are localized in the center of the proximal pars distalis enveloping both sides of the neurohypophysis. LH cells form a continuous population throughout the PPD, while FSH cells are more loosely distributed throughout the same area and form small aggregations. Marked annual changes were encountered in gonadosomatic index (GSI), follicle diameter, mRNA levels and protein levels of FSH and LH. From September to November, all fish had low GSI, and the ovary contained previtellogenic follicles. From December, the GSI level increased and remained high until March, the follicular diameter reached its maximum in January, where the ovary contained large fully grown follicles. Thereafter, spawning occurred through March and April and ended in May, and GSI level and follicle diameter increased again; and the ovary contained mid-vitellogenic follicles. LH pituitary content and mRNA levels were low at pre- and early vitellogenesis, increasing gradually during this process to reach a peak of LH mRNA levels in mid vitellogenic ovary and a peak of LH content in fully grown ovarian follicles. However, no significant change occurred in FSH pituitary content and mRNA levels in vitellogenic fish and in fish during final maturation stages. A dramatic difference was found in the total content of each gonadotropin in the pituitary, with higher LH than FSH. Moreover, follicle diameter was positively and significantly correlated with LH pituitary content and its transcript levels – but not with the pituitary content or mRNA levels of FSH. Taken together, these results indicate that in carp, LH alone is sufficient to regulate both vitellogenesis and final oocyte maturation while FSH may have another, yet undefined role.
2017
Levavi-Sivan, B. ; G, D. ; A, H. Vitellogenin Level in the Plasma of Russian Sturgeon (Acipenser gueldenstaedtii) Northern Israel. Journal of Marine Science: Research & Development 2017, 7 244. Publisher's VersionAbstract

In the present study, we examined the vitellogenin (Vg) level of Russian sturgeon maintained in a relatively constant aquaculture at a water temperature of 18-22°C during growth and maturation.

An increase in Vg in the blood plasma from oocytes was found in the yellow oocytes stage to the gray oocytes stage. However, no Vg was found in the pre-vitellogenic stage. Based on the present study and previous studies on hormone control reproduction and growth, we proposed a quality model that correlated between egg development and the hormones involved in controlling vitelogenesis (VTL).

Aizen, J. ; Hollander-Cohen, L. ; Shpilman, M. ; Levavi-Sivan, B. Biologically active recombinant carp LH as a spawning-inducing agent for carp. Journal of Endocrinology 2017, 232. Publisher's Version
Sanchís-Benlloch, P. J. ; Nocillado, J. ; Ladisa, C. ; Aizen, J. ; Miller, A. ; Shpilman, M. ; Levavi-Sivan, B. ; Ventura, T. ; Elizur, A. In-vitro and in-vivo biological activity of recombinant yellowtail kingfish (Seriola lalandi) follicle stimulating hormone. General and Comparative Endocrinology 2017, 241, 41 - 49. Publisher's VersionAbstract
Biologically active recombinant yellowtail kingfish follicle stimulating hormone (rytkFsh) was produced in yeast Pichia pastoris and its biological activity was demonstrated by both in-vitro and in-vivo bioassays. Incubation of ovarian and testicular fragments with the recombinant hormone stimulated E2 and 11-KT secretion, respectively. In-vivo trial in immature female YTK resulted in a significant increase of plasma E2 levels and development of oocytes. In males at the early stages of puberty, advancement of spermatogenesis was observed, however plasma 11-KT levels were reduced when administered with rytkFsh.
Spicer, O. S. ; Zmora, N. ; Wong, T. - T. ; Golan, M. ; Levavi-Sivan, B. ; Gothilf, Y. ; Zohar, Y. The gonadotropin-inhibitory hormone (Lpxrfa) system's regulation of reproduction in the brain–pituitary axis of the zebrafish (Danio rerio)†. Biology of Reproduction 2017, 96, 1031-1042. Publisher's VersionAbstract
Gonadotropin-inhibitory hormone (GNIH) was discovered in quail with the ability to reduce gonadotropin expression/secretion in the pituitary. There have been few studies on GNIH orthologs in teleosts (LPXRFamide (Lpxrfa) peptides), which have provided inconsistent results. Therefore, the goal of this study was to determine the roles and modes of action by which Lpxrfa exerts its functions in the brain–pituitary axis of zebrafish (Danio rerio). We localized Lpxrfa soma to the ventral hypothalamus, with fibers extending throughout the brain and to the pituitary. In the preoptic area, Lpxrfa fibers interact with gonadotropin-releasing hormone 3 (Gnrh3) soma. In pituitary explants, zebrafish peptide Lpxrfa-3 downregulated luteinizing hormone beta subunit and common alpha subunit expression. In addition, Lpxrfa-3 reduced gnrh3 expression in brain slices, offering another pathway for Lpxrfa to exert its effects on reproduction. Receptor activation studies, in a heterologous cell-based system, revealed that all three zebrafish Lpxrfa peptides activate Lpxrf-R2 and Lpxrf-R3 via the PKA/cAMP pathway. Receptor activation studies demonstrated that, in addition to activating Lpxrf receptors, zebrafish Lpxrfa-2 and Lpxrfa-3 antagonize Kisspeptin-2 (Kiss2) activation of Kisspeptin receptor-1a (Kiss1ra). The fact that kiss1ra-expressing neurons in the preoptic area are innervated by Lpxrfa-ir fibers suggests an additional pathway for Lpxrfa action. Therefore, our results suggest that Lpxrfa may act as a reproductive inhibitory neuropeptide in the zebrafish that interacts with Gnrh3 neurons in the brain and with gonadotropes in the pituitary, while also potentially utilizing the Kiss2/Kiss1ra pathway.
Simon, Y. ; Levavi-Sivan, B. ; Cahaner, A. ; Hulata, G. ; Antler, A. ; Rozenfeld, L. ; Halachmi, I. A behavioural sensor for fish stress. Aquacultural Engineering 2017, 77, 107 - 111. Publisher's VersionAbstract
Due to water turbidity, fish stress might be difficult to observe. Evaluation of fish stress by blood sampling requires removing a fish from the water, which is in itself a stressful event. Therefore, we designed and built a sensor to detect fish behaviour that reflects stress. The electronic sensor detected early signs of fish stress by scoring the fish's inactivity. LEDs and detectors are embedded on a steel wand that is held underwater by an operator. In this preliminary (feasibility) study, the new sensor was validated for Tilapia (Cichlidae) and Hybrid Striped Bass (Morone). We induced stressful situations in the fish tanks by manipulating oxygen and temperature levels. Results Lowering the temperature and oxygen levels both significantly increased the average number of signals identified by the sensor, which indicate stress. The effect of reducing water temperature from 24°C to 15°C was three times stronger than was the effect of lowering the oxygen saturation level from 85% to 50%. The difference in the number of signals between the good and stressful conditions was statistically significant, amounting to approximately eight sensor signals, 10.57 compared to 2.49 respectively. Lowering the temperature increased the mean number of signals by 5.85 and 6.06 at 85% and 50% oxygen saturation respectively, whereas lowering oxygen levels increased the mean number of signals by 2.02 and 2.23 at 24°C and 15°C, respectively. The results indicate that the stress status of cultured fish can be evaluated using the proposed behavioural sensor. The new sensor may provide an earlier indication of a problem in a fish tank or pond than was heretofore possible. This early warning can enable the fish farmer to take action before many fish are harmed.
Zmora, N. ; Wong, T. - T. ; Stubblefield, J. ; Levavi-Sivan, B. ; Zohar, Y. Neurokinin B regulates reproduction via inhibition of kisspeptin in a teleost, the striped bass. Journal of Endocrinology 2017, 233. Publisher's Version
2016
Yom-Din, S. ; Hollander-Cohen, L. ; Aizen, J. ; Boehm, B. ; Shpilman, M. ; Golan, M. ; Hurvitz, A. ; Degani, G. ; Levavi-Sivan, B. Gonadotropins in the Russian sturgeon: Their role in steroid secretion and the effect of hormonal treatment on their secretion. PLoS ONE 2016, 11. Publisher's Version
Golan, M. ; Martin, A. O. ; Mollard, P. ; Levavi-Sivan, B. Anatomical and functional gonadotrope networks in the teleost pituitary. 2016, 6 23777. Publisher's VersionAbstract
Mammalian pituitaries exhibit a high degree of intercellular coordination; this enables them to mount large-scale coordinated responses to various physiological stimuli. This type of communication has not been adequately demonstrated in teleost pituitaries, which exhibit direct hypothalamic innervation and expression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in distinct cell types. We found that in two fish species, namely tilapia and zebrafish, LH cells exhibit close cell–cell contacts and form a continuous network throughout the gland. FSH cells were more loosely distributed but maintained some degree of cell–cell contact by virtue of cytoplasmic processes. These anatomical differences also manifest themselves at the functional level as evidenced by the effect of gap-junction uncouplers on gonadotropin release. These substances abolished the LH response to gonadotropin-releasing hormone stimulation but did not affect the FSH response to the same stimuli. Dye transfer between neighboring LH cells provides further evidence for functional coupling. The two gonadotropins were also found to be differently packaged within their corresponding cell types. Our findings highlight the evolutionary origin of pituitary cell networks and demonstrate how the different levels of cell–cell coordination within the LH and FSH cell populations are reflected in their distinct secretion patterns.
Golan, M. ; Hollander-Cohen, L. ; Levavi-Sivan, B. Stellate Cell Networks in the Teleost Pituitary. 2016, 6 24426. Publisher's VersionAbstract
The folliculostellate cells of the mammalian pituitary are non-endocrine cells that are implicated in long-distance communication and paracrine signaling, but to date, these cells have yet to be characterized in teleosts. We found that the stellate cells of the teleost pituitary share many common attributes with mammalian folliculostellate cells. By labeling of stellate cells in live preparations of tilapia pituitaries we investigated their distribution, association with other endocrine cells and their anatomical and functional coupling. In the pars intermedia, stellate cells were arranged around neuronal bundles and their processes extended into the pars distalis. Within the pars distalis, stellate cells formed close associations with FSH cells and, to a lesser degree, with GH and LH cells, suggesting differential paracrine regulation of the two gonadotrope populations. The production of follistatin by stellate cells further corroborates the notion of a paracrine role on FSH release. We also found stellate cells to form gap junctions that enabled dye transfer to neighboring stellate cells, implicating that these cells form a large-scale network that connects distant parts of the pituitary. Our findings represent the first wide-scale study of stellate cells in teleosts and provide valuable information regarding their functional roles in pituitary function.