Seasonal changes of brain GnRH-I, -II, and -III during the final reproductive period in adult male and female sea lamprey

Waterborne pheromones modulate gonadotropin-inhibitory hormone levels in sea lamprey (Petromyzon marinus)

The relationships between pheromone stimuli and neuropeptides are not well established in vertebrates due to the limited number of unequivocally identified pheromone molecules. The sea lamprey (Petromyzon marinus) is an advantageous vertebrate model to study the effects of pheromone exposure on neuropeptides since many pheromone molecules and neuropeptides have been identified in this species. Sexually mature male sea lamprey release pheromones 7α, 12α, 24-trihydroxy-5α-cholan-3-one 24-sulfate (3 keto-petromyzonol sulfate, 3kPZS) and 7α, 12α-dihydroxy-5α-cholan-3-one-24-oic acid (3-keto allocholic acid, 3kACA) that differentially regulate gonadotropin-releasing hormone (lGnRH) and steroid levels in sexually immature sea lamprey. However, the effects of these pheromones on gonadotropin-inhibitory hormones (GnIHs), hypothalamic neuropeptides that regulate lGnRH release, are still elusive. In this report, we sought to examine the effects of waterborne pheromones on lamprey GnIH-related neuropeptide levels in sexually immature sea lamprey. Ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) analyses revealed sex differences in GnIH-related neuropeptide levels in the brain and plasma of immature sea lamprey. Exposure to 3kPZS and 3kACA exerted differential effects on GnIH-related neuropeptide levels in both sexes, but the effects were more prominent in female brains. We conclude that sea lamprey pheromones regulate GnIH-related neuropeptide levels in a sexually dimorphic manner.

Co-localization of three gonadotropin-releasing hormone transcripts in larval, parasitic, and adult sea lamprey brains

RNA expression of lamprey gonadotropin-releasing hormone (lGnRH)-I, -II, and -III was demonstrated in the brains of larval, parasitic phase and adult sea lampreys, Petromyzon marinus, using a highly sensitive triple-label in situ hybridization technique. In female larval lampreys, lGnRH-I and-II were co-expressed in the same neurons throughout the olfactory bulbs, preoptic area (POA), and rhombencephalon (hindbrain); lGnRH-I, -II and -III were triple co-expressed in the hypothalamus and in the paranuclear region of neuronal somas in the rhombencephalon. In female parasitic phase lampreys, lGnRH-I and -II were co-expressed in the POA, thalamus, and preoptico-neurohypophyseal tract (PNT); lGnRH-III was minimally triple co-expressed with lGnRH-I and -II in the hypothalamus. In adult female lampreys, lGnRH-I and -III were co-expressed in the hypothalamus; lGnRH-I was also expressed in the neurohypophysis (NH). In adult male lampreys, lGnRH-I and-III were co-expressed in the primordial hippocampus, POA, thalamus, hypothalamus, NH, and PNT; lGnRH-I was also expressed in the epithalamus. In summary, we provide the first study using in situ hybridization of all three lGnRHs (lGnRH-I, -II, and -III) at three major life stages (larval, parasitic, and adult) of lampreys, which strongly supports previous immunohistological studies and suggests that lGnRH-I and -II are the predominant lGnRHs in larval and parasitic phase lampreys, and that lGnRH-I and -III are the predominant lGnRHs in adult female and male lampreys. Therefore, our results show that lGnRH-I, -II, and -III have different localization and co-expression in the development and sexual maturation of lampreys, which may suggest unique physiological roles at each life stage and sex in the developing and mature lamprey brain.

Expression of two glycoprotein hormone receptors in larval, parasitic phase, and adult sea lampreys

All jawed vertebrates have three canonical glycoprotein hormones (GpHs: luteinizing hormone, LH; follicle stimulating hormone, FSH; and thyroid stimulating hormone, TSH) with three corresponding GpH receptors (GpH-Rs: LH-R, FSH-R, and TSH-R). In contrast, we propose that the jawless vertebrate, the sea lamprey (Petromyzon marinus), only has two pituitary glycoprotein hormones, lamprey (l)GpH and l-thyrostimulin, and two functional glycoprotein receptors, lGpH-R I and II. It is not known at this time whether there is a specific receptor for lGpH and l-thyrostimulin, or if both GpHs can differentially activate the lGpH-Rs. In this report, we determined the RNA expression of lGpH-R I and II in the gonads and thyroids of larval, parasitic phase, and adult lampreys. A highly sensitive dual-label fluorescent in situ hybridization technique (RNAScope™) showed lGpH-R I expression in the ovaries of larval lamprey, and co-localization and co-expression of lGpH-R I and II in the ovaries of parasitic phase and adult lampreys. Both receptors were also highly co-localized and co-expressed in the endostyle of larval lamprey and thyroid follicles of parasitic and adult lampreys. In addition, we performed in vivo studies to determine the actions of lamprey gonadotropin releasing hormones (lGnRHs) on lGpH-R I and II expression by real time PCR, and determined plasma concentrations of estradiol and thyroxine. Administration of lGnRH-III significantly (p ≤ 0.01) increased lGpHR II expression in the thyroid follicles of adult female lampreys but did not cause a significant increase in RNA expression of lGpH-R I and II in ovaries. Concomitantly, there was a significant increase (p ≤ 0.01) of plasma estradiol without any significant changes of plasma thyroxine concentrations in response to treatment to lGnRH-I, -II, or -III. In summary, our results provide supporting evidence that the lamprey pituitary glycoprotein hormones may differentially activate the lamprey GpH-Rs in regulating both thyroid and gonadal activities during each of the three life stages of the sea lamprey.

A second estrogen receptor from Japanese lamprey (Lethenteron japonicum) does not have activities for estrogen binding and transcription

Estrogens regulate many physiological responses in vertebrates by binding to the estrogen receptor (ER), a ligand-activated transcription factor. To understand the evolution of vertebrate ERs and to investigate how estrogen acts in a jawless vertebrate, we used degenerate primer sets and PCR to isolate DNA fragments encoding two distinct ER subtypes, Esr1a and Esr1b from the Japanese lamprey, Lethenteron japonicum. Phylogenetic analysis indicates that these two ERs are the result of lineage-specific gene duplication within the jawless fishes, different from the previous duplication event of Esr1 (ERα) and Esr2 (ERβ) within the jawed vertebrates. Reporter gene assays show that lamprey Esr1a displays both constitutive and estrogen-dependent activation of gene transcription. Domain swapping experiments indicate that constitutive activity resides in the A/B domain of lamprey Esr1a. Unexpectedly, lamprey Esr1b does not bind estradiol and is not stimulated by other estrogens, androgens or corticosteroids. A 3D model of lamprey Esr1b suggests that although estradiol fits into the steroid binding site, some stabilizing contacts between the ligand and side chains that are found in human Esr1 and Esr2 are missing in lamprey Esr1b.

Identification and quantification of sea lamprey gonadotropin-releasing hormones by electrospray ionization tandem mass spectrometry

Gonadotropin-releasing hormones (GnRH) are neuropeptide hormones that regulate reproduction in vertebrates. Twenty-five unique chordate GnRH isoforms have been identified, all with very similar molecular architecture. Identification and quantification of endogenous GnRH in biological samples is extremely challenging due to the high levels of sequence similarity among these GnRH peptides and complexity of the biological matrices laden with large numbers of other peptides and protein degradation fragments, and due to low levels of GnRH abundance. In this study, three lamprey GnRH (lGnRH-I, -II, and -III) were extracted from sea lamprey brain tissue and plasma samples by solid-phase extraction (SPE) and identified by a high resolution Q-TOF mass spectrometry (MS). A rapid quantitation method was developed and validated to determine the concentrations of these three lGnRHs by using a UPLC coupled tandem MS in positive ESI multiple reaction monitoring (MRM) mode. Luteinizing hormone-release hormone (LHRH, one of the mammalian GnRHs) was used as the internal standard. The developed quantitation method was fully validated for its recovery, matrix effect, linearity, repeatability, precision and accuracy, and storage stability. This method exhibited excellent linearity in a broad concentration range for all three lGnRHs (R(2)>0.99) and limits of detection (LOD; as low as 0.007 ng/mL). Brain and plasma samples from a total of 280 sea lampreys were analyzed with the developed method to investigate the biological relevance of the lGnRH levels. The concentrations of these three lGnRHs were detected at levels of pictogram per microgram brain tissue and milliliter of plasma. The obtained analytical performance parameters and collected data from real biological samples have proven that this is a robust, sensitive, and fully validated LC-MS/MS method to simultaneously quantify three neuropeptide hormones in complex biological matrices.

Cloning, phylogeny, and regional expression of a Y5 receptor mRNA in the brain of the sea lamprey (Petromyzon marinus)

The NPY receptors known as Y receptors are classified into three subfamilies, Y1, Y2, and Y5, and are involved in different physiological functions. The Y5 receptor is the only member of the Y5 subfamily, and it is present in all vertebrate groups, except for teleosts. Both molecular and pharmacological studies show that Y5 receptor is highly conserved during vertebrate evolution. Furthermore, this receptor is widely expressed in the mammalian brain, including the hypothalamus, where it is thought to take part in feeding and homeostasis regulation. Lampreys belong to the agnathan lineage, and they are thought to have branched out between the two whole-genome duplications that occurred in vertebrates. Therefore, they are in a key position for studies on the evolution of gene families in vertebrates. Here we report the cloning, phylogeny, and brain expression pattern of the sea lamprey Y5 receptor. In phylogenetic studies, the lamprey Y5 receptor clusters in a basal position, together with Y5 receptors of other vertebrates. The mRNA of this receptor is broadly expressed in the lamprey brain, being especially abundant in hypothalamic areas. Its expression pattern is roughly similar to that reported for other vertebrates and parallels the expression pattern of the Y1 receptor subtype previously described by our group, as it occurs in mammals. Altogether, these results confirm that a Y5 receptor is present in lampreys, thus being highly conserved during the evolution of vertebrates, and suggest that it is involved in many brain functions, the only known exception being teleosts.

Integrative neuro-endocrine pathways in the control of reproduction in lamprey: a brief review

The gonadotropin-releasing hormone (GnRH) system is well known as the main regulator of reproductive physiology in vertebrates. It is also part of a network of brain structures and pathways that integrate information from the internal and external milieu and coordinate the adaptive behavioral and physiological responses to social and reproductive survival needs. In this paper we review the state of knowledge of the GnRH system in relation to the behavior, external, and internal factors that control reproduction in one of the oldest lineage of vertebrates, the lampreys.

An anti-steroidogenic inhibitory primer pheromone in male sea lamprey (Petromyzon marinus)

Reproductive functions can be modulated by both stimulatory and inhibitory primer pheromones released by conspecifics. Many stimulatory primer pheromones have been documented, but relatively few inhibitory primer pheromones have been reported in vertebrates. The sea lamprey male sex pheromone system presents an advantageous model to explore the stimulatory and inhibitory primer pheromone functions in vertebrates since several pheromone components have been identified. We hypothesized that a candidate sex pheromone component, 7α, 12α-dihydroxy-5α-cholan-3-one-24-oic acid (3 keto-allocholic acid or 3kACA), exerts priming effects through the hypothalamic-pituitary-gonadal (HPG) axis. To test this hypothesis, we measured the peptide concentrations and gene expressions of lamprey gonadotropin releasing hormones (lGnRH) and the HPG output in immature male sea lamprey exposed to waterborne 3kACA. Exposure to waterborne 3kACA altered neuronal activation markers such as jun and jun N-terminal kinase (JNK), and lGnRH mRNA levels in the brain. Waterborne 3kACA also increased lGnRH-III, but not lGnRH-I or -II, in the forebrain. In the plasma, 3kACA exposure decreased all three lGnRH peptide concentrations after 1h exposure. After 2h exposure, 3kACA increased lGnRH-I and -III, but decreased lGnRH-II peptide concentrations in the plasma. Plasma lGnRH peptide concentrations showed differential phasic patterns. Group housing condition appeared to increase the averaged plasma lGnRH levels in male sea lamprey compared to isolated males. Interestingly, 15α-hydroxyprogesterone (15α-P) concentrations decreased after prolonged 3kACA exposure (at least 24h). To our knowledge, this is the only known synthetic vertebrate pheromone component that inhibits steroidogenesis in males.

Expression of three GnRH receptors in specific tissues in male and female sea lampreys Petromyzon marinus at three distinct life stages

Two recently cloned gonadotropin-releasing hormone (GnRH) receptors (lamprey GnRH-R-2 and lamprey GnRH-R-3) along with lamprey (l) GnRH-R-1 were shown to share similar structural features and amino acid motifs common to other vertebrate receptors. Here we report on our findings of RNA expression of these three GnRH receptors in the three major life stages (larval, parasitic, and adult phases) of the sea lamprey, Petromyzon marinus, a basal vertebrate. For each stage, we examined the expression of messenger RNA encoding the receptors in the brain, pituitary, gonad, heart, muscle, liver, eye, intestine, kidney, skin, thyroid, gill, and endostyle by RT-PCR. In adult lampreys, the spatial expression of the three receptors in the brain and pituitary was investigated by in situ hybridization. In general, the receptors were more widely expressed in adult tissues as compared to parasitic-phase tissues and least widely expressed in the larval tissues. There were noted differences in male and female lampreys in the adult and parasitic phases for all three receptors. The data showed the presence of all three receptor transcripts in brain tissues for adult and parasitic phases and all three receptor transcripts were expressed in the adult pituitaries, but not in the parasitic pituitaries. However, in the larval phase, only lGnRH-R-1 was expressed in the larval brain and pituitary. In situ hybridization revealed that lGnRH-R-2 and -3 were expressed in the pineal tissue of adult female lampreys while lGnRH-R-1 was expressed in the pineal in adult male lampreys, all restricted to the pineal pellucida. In summary, these data provide an initial comparative analysis of expression of three lamprey GnRH receptors suggesting differential regulation within males and females at three different life/reproductive stages.

Glycoprotein hormone in the pituitary of hagfish and its evolutionary implications

The pituitary gland is present in all vertebrates, from agnathans (jawless vertebrates) to mammals, but not in invertebrates. Reproduction in gnathostomes (jawed vertebrates) is controlled by two pituitary gonadotropins (GTHs), luteinizing hormone and follicle-stimulating hormone, which are part of the pituitary glycoprotein hormone (GPH) family. Hagfishes, which lack both jaws and vertebrae, are considered the most primitive vertebrate known, living or extinct. Accordingly, they are of particular importance in understanding the evolution of the pituitary GPHs and their functions related to vertebrate reproduction. Nevertheless, key elements of the reproductive endocrine system in hagfish have yet to be elucidated. Our current report has revealed the first identification of a functional GPH composed of two subunits that possess gonadotropic action at the pituitary of brown hagfish. It seems most likely that an ancestral GPH gave rise to only one GTH in hagfish pituitary and that multiplicity of GPHs arose later during the early evolution of gnathostomes. This paper briefly summarizes the latest findings on the hagfish GPH from an evolutionary point of view.

Pheromonal bile acid 3-ketopetromyzonol sulfate primes the neuroendocrine system in sea lamprey

BACKGROUND

Vertebrate pheromones are known to prime the endocrine system, especially the hypothalamic-pituitary-gonadal (HPG) axis. However, no known pheromone molecule has been shown to modulate directly the synthesis or release of gonadotropin releasing hormone (GnRH), the main regulator of the HPG axis. We selected sea lamprey (Petromyzon marinus) as a model system to determine whether a single pheromone component alters the output of GnRH.Sea lamprey male sex pheromones contain a main component, 7α, 12α, 24-trihydroxy-5α-cholan-3-one 24-sulfate (3 keto-petromyzonol sulfate or 3kPZS), which has been shown to modulate behaviors of mature females. Through a series of experiments, we tested the hypothesis that 3kPZS modulates both synthesis and release of GnRH, and subsequently, HPG output in immature sea lamprey.

RESULTS

The results showed that natural male pheromone mixtures induced differential steroid responses but facilitated sexual maturation in both sexes of immature animals (χ(2) = 5.042, dF = 1, p < 0.05). Exposure to 3kPZS increased plasma 15α-hydroxyprogesterone (15α-P) concentrations (one-way ANOVA, p < 0.05) and brain gene expressions (genes examined: three lamprey (l) GnRH-I transcripts, lGnRH-III, Jun and Jun N-terminal kinase (JNK); one-way ANOVA, p < 0.05), but did not alter the number of GnRH neurons in the hypothalamus in immature animals. In addition, 3kPZS treatments increased lGnRH peptide concentrations in the forebrain and modulated their levels in plasma. Overall, 3kPZS modulation of HPG axis is more pronounced in immature males than in females.

CONCLUSIONS

We conclude that a single male pheromone component primes the HPG axis in immature sea lamprey in a sexually dimorphic manner.

Molecular cloning and pharmacological characterization of two novel GnRH receptors in the lamprey (Petromyzon marinus)

This paper reports the identification, expression, binding kinetics, and functional studies of two novel type III lamprey GnRH receptors (lGnRH-R-2 and lGnRH-R-3) in the sea lamprey, a basal vertebrate. These novel GnRH receptors share the structural features and amino acid motifs common to other known gnathostome GnRH receptors. The ligand specificity and activation of intracellular signaling studies showed ligands lGnRH-II and -III induced an inositol phosphate (IP) response at lGnRH-R-2 and lGnRH-R-3, whereas the ligand lGnRH-I did not stimulate an IP response. lGnRH-II was a more potent activator of lGnRH-R-3 than lGnRH-III. Stimulation of lGnRH-R-2 and lGnRH-R-3 testing all three lGnRH ligands did not elicit a cAMP response. lGnRH-R-2 has a higher binding affinity in response to lGnRH-III than lGnRH-II, whereas lGnRH-R-3 has a higher binding affinity in response to lGnRH-II than IGnRH-III. lGnRH-R-2 precursor transcript was detected in a wide variety of tissues including the pituitary whereas lGnRH-R-3 precursor transcript was not as widely expressed and primarily expressed in the brain and eye of male and female lampreys. From our phylogenetic analysis, we propose that lGnRH-R-1 evolved from a common ancestor of all vertebrate GnRH receptors and lGnRH-R-2 and lGnRH-R-3 likely occurred due to a gene duplication within the lamprey lineage. In summary, we propose from our findings of receptor subtypes in the sea lamprey that the evolutionary recruitment of specific pituitary GnRH receptor subtypes for particular physiological functions seen in later evolved vertebrates was an ancestral character that first arose in a basal vertebrate.

Effects of lamprey PQRFamide peptides on brain gonadotropin-releasing hormone concentrations and pituitary gonadotropin-β mRNA expression

Within the RFamide peptide family, PQRFamide peptides that include neuropeptide FF and AF possess a C-terminal Pro-Gln-Arg-Phe-NH(2) motif. We previously identified PQRFamide peptides, lamprey PQRFa, PQRFa-related peptide (RP)-1 and -RP-2 by immunoaffinity purification in the brain of lamprey, one of the most ancient vertebrate species [13]. Lamprey PQRFamide peptide precursor mRNA was expressed in regions predicted to be involved in neuroendocrine regulation in the hypothalamus. However, the putative function(s) of lamprey PQRFamide peptides (PQRFa, PQRFa-RP-1 and PQRFa-RP-2) were not examined nor was the distribution of PQRFamide peptides examined in other tissues besides the brain. The objective of this study was to determine tissue distribution of lamprey PQRFamide peptide precursor mRNA, and to examine the effects of PQRFamide peptides on brain gonadotropin-releasing hormone (GnRH)-I, -II, and -III protein concentrations, and pituitary gonadotropin (GTH)-β mRNA expression in adult lampreys. Lamprey PQRFamide peptide precursor mRNA was expressed in the eye and the brain. Lamprey PQRFa at 100 μg/kg increased brain concentrations of lamprey GnRH-II compared with controls. PQRFa, PQRFa-RP-1 and PQRFa-RP-2 did not significantly change brain protein concentrations of either lamprey GnRH-I, -III, or lamprey GTH-β mRNA expression in the pituitary. These data suggest that one of the PQRFamide peptides may act as a neuroregulator of at least the lamprey GnRH-II system in adult female lamprey.

Evolutionary origin of the structure and function of gonadotropin-inhibitory hormone: insights from lampreys

Gonadotropin (GTH)-inhibitory hormone (GnIH) is a novel hypothalamic neuropeptide that inhibits GTH secretion in mammals and birds by acting on gonadotropes and GnRH neurons within the hypothalamic-pituitary-gonadal axis. GnIH and its orthologs that have an LPXRFamide (X = L or Q) motif at the C terminus (LPXRFamide peptides) have been identified in representative species of gnathostomes. However, the identity of an LPXRFamide peptide had yet to be identified in agnathans, the most ancient lineage of vertebrates, leaving open the question of the evolutionary origin of GnIH and its ancestral function(s). In this study, we identified an LPXRFamide peptide gene encoding three peptides (LPXRFa-1a, LPXRFa-1b, and LPXRFa-2) from the brain of sea lamprey by synteny analysis and cDNA cloning, and the mature peptides by immunoaffinity purification and mass spectrometry. The expression of lamprey LPXRFamide peptide precursor mRNA was localized in the brain and gonad by RT-PCR and in the hypothalamus by in situ hybridization. Immunohistochemistry showed appositions of lamprey LPXRFamide peptide immunoreactive fibers in close proximity to GnRH-III neurons, suggesting that lamprey LPXRFamide peptides act on GnRH-III neurons. In addition, lamprey LPXRFa-2 stimulated the expression of lamprey GnRH-III protein in the hypothalamus and GTHβ mRNA expression in the pituitary. Synteny and phylogenetic analyses suggest that the LPXRFamide peptide gene diverged from a common ancestral gene likely through gene duplication in the basal vertebrates. These results suggest that one ancestral function of LPXRFamide peptides may be stimulatory compared with the inhibitory function seen in later-evolved vertebrates (birds and mammals).

Social Regulation of Gene Expression in the Hypothalamic-Pituitary-Gonadal Axis

Reproduction is a critically important event in every animals' life and in all vertebrates is controlled by the brain via the hypothalamic-pituitary-gonadal (HPG) axis. In many species, this axis, and hence reproductive fitness, can be profoundly influenced by the social environment. Here, we review how the reception of information in a social context causes genomic changes at each level of the HPG axis.