Update: brain and pituitary hormones of lampreys

Strong genome-wide divergence between sympatric European river and brook lampreys

Lampreys, together with hagfishes, are the only extant representatives of jawless vertebrates and thus of prime interest for the study of vertebrate evolution [1]. Most lamprey genera occur in two forms with divergent life histories: a parasitic, anadromous and a non-parasitic, freshwater resident form [2-8]. The taxonomic status of such 'paired species' is disputed, however. While indistinguishable at larval stages, but clearly distinct as adults, they cannot be differentiated with available genetic data [6,7], which has fuelled speculations that the two forms may in fact represent products of phenotypic plasticity within a single species. Here, we use restriction site-associated DNA sequencing (RADseq) to examine the genetic population structure of sympatric European river (Lampetra fluviatilis L., 1758) and brook (Lampetra planeri Bloch, 1784) lampreys. We find strong genetic differentiation and identify numerous fixed and diagnostic single nucleotide polymorphisms (SNPs) between the two species, 12 of which can be unequivocally assigned to specific genes.

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.

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.

Evolution of vertebrate GnRH receptors from the perspective of a Basal vertebrate

This minireview provides the current status on gonadotropin-releasing hormone receptors (GnRH-R) in vertebrates, from the perspective of a basal vertebrate, the sea lamprey, and provides an evolutionary scheme based on the recent advance of whole genome sequencing. In addition, we provide a perspective on the functional divergence and evolution of the receptors. In this review we use the phylogenetic classification of vertebrate GnRH receptors that groups them into three clusters: type I (mammalian and non-mammalian), type II, and type III GnRH receptors. New findings show that the sea lamprey has two type III-like GnRH receptors and an ancestral type GnRH receptor that is more closely related to the type II-like receptors. These two novel GnRH receptors along with lGnRH-R-1 share similar structural features and amino acid motifs common to other known gnathostome type II/III receptors. Recent data analyses of the lamprey genome provide strong evidence that two whole rounds of genome duplication (2R) occurred prior to the gnathostome-agnathan split. Based on our current knowledge, it is proposed that lGnRH-R-1 evolved from an ancestor of the type II receptor following a vertebrate-shared genome duplication and that the two type III receptors resulted from a duplication within lamprey of a gene derived from a lineage shared by many vertebrates.

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

Sea lampreys are anadromous and semelparous, i.e., they spawn only once in their lifetime, after which they die. Sexual maturation is thus a synchronized process coordinated with the life stages of the lamprey. Recently, a novel gonadotropin-releasing hormone, lamprey GnRH-II (lGnRH-II), was identified in lampreys and suggested to have a hypothalamic role in reproduction (Kavanaugh et al., 2008). To further understand the role of lGnRH-II, changes in ovarian morphology, brain gonadotropin-releasing hormone (lGnRH-I, -II, and -III), and plasma estradiol were examined during the final two months of the reproductive season of adult male and female sea lamprey. The results showed significant correlations between water temperature, fluctuation of brain GnRHs, plasma estradiol and reproductive stages during this time. In males, lGnRH-I concentration increased early in the season, peaked, then declined with a subsequent increase with the final maturational stages. In comparison, lGnRH-II and -III concentrations were also elevated early in the season in males, dropped and then peaked in mid-season with a subsequent decline of lGnRH-II or increase of lGnRH-III at spermiation. In females, lGnRH-III concentration peaked in mid-season with a drop at ovulation while lGnRH-I remained unchanged during the season. In contrast, lGnRH-II concentrations in females were elevated at the beginning of the season and then dropped and remained low during the rest of the season. In summary, these data provide evidence that there are seasonal and differential changes of the three GnRHs during this final reproductive period suggesting specific roles for each of the GnRHs in male and female reproduction.

Neuroendocrine and behavioral responses to weak electric fields in adult sea lampreys (Petromyzon marinus)

We characterized the behavioral and neuroendocrine responses of adult sea lampreys (Petromyzon marinus) to weak electric fields. Adult sea lampreys, captured during upstream spawning migration, exhibited limited active behaviors during exposure to weak electric fields and spent the most time attached to the wall of the testing arena near the cathode (-). For adult male sea lampreys, exposure to weak electric fields resulted in increased lamprey (l) GnRH-I mRNA expression but decreased lGnRH-I immunoreactivities in the forebrain, and decreased Jun (a neuronal activation marker) mRNA levels in the brain stem. Similar effects were not observed in the brains of female sea lampreys after weak electric field stimulation. The influence of electroreception on forebrain lGnRH suggests that electroreception may modulate the reproductive systems in adult male sea lampreys. The changes in Jun expression may be associated with swimming inhibition during weak electric field stimulation. The results for adult sea lampreys are the opposite of those obtained using parasitic-stage sea lampreys, which displayed increased activity during and after cathodal stimulation. Our results demonstrate that adult sea lampreys are sensitive to weak electric fields, which may play a role in reproduction. They also suggest that electrical stimuli mediate different behaviors in feeding-stage and spawning-stage sea lampreys.

Sex steroids and their receptors in lampreys

The use of steroids and their receptors as ligand-gated transcription factors is thought to be an important step in vertebrate evolution. The lamprey is the earliest-evolving vertebrate to date in which sex steroids and their receptors have been demonstrated to have hormonal roles similar to those found in jawed vertebrates. Sex steroids and their receptors have been examined in several lamprey species, and the majority of studies have focused on the sea lamprey, Petromyzon marinus. While classical steroids appear to be present in lampreys, their function, concentrations, and synthesis have not been determined conclusively. The only classical steroid that is thought to act as a hormone in both males and females is estradiol. Recent research has established that lampreys produce and circulate 15alpha-hydroxylated steroids, and that these steroids respond to upstream stimulation within the hypothalamic-pituitary-gonadal axis. In particular, 15alpha-hydroxyprogesterone is highly sensitive and responds in great magnitude to stimulation, and is likely a hormone. Lampreys also appear to use androstenedione, a precursor to vertebrate androgens, as their main androgen, and a receptor for androstenedione has recently been described. Non-classical steroids are prevalent in many aquatic vertebrates, and the non-classical steroids found in the sea lamprey may represent an evolutionary artifact, or alternatively may be a way to avoid endocrine disruption when ingesting the body fluids of host fish. The lamprey will continue to be an interesting model for examining the evolution of steroid hormones, steroid receptors, and steroid function.

Dose-response relationship of 15alpha-hydroxylated sex steroids to gonadotropin-releasing hormones and pituitary extract in male sea lampreys (Petromyzon marinus)

The sea lamprey (Petromyzon marinus) is one of the earliest extant vertebrates for which the hypothalamic-pituitary-gonadal (HPG) axis has been shown to control and regulate reproduction in a similar fashion to gnathostome vertebrates. While the two forms of gonadotropin-releasing hormones in the sea lamprey (GnRH I and GnRH III) have been studied extensively, their in vivo effect on synthesis of 15alpha-hydroxytestosterone (15alpha-T) and 15alpha-hydroxyprogesterone (15alpha-P) have only been partially characterized. In the present study, plasma concentrations of 15alpha-T and 15alpha-P were measured in prespermiating sea lampreys that were given a single injection of either GnRH I or GnRH III in doses ranging from 5 to 100 microg/kg, or of pituitary extract (as a source of gonadotropin). Plasma was sampled at 1-6h and 6-48 h post-injection, in separate experiments, in order to characterize the peak and duration of responses. 15alpha-T plasma concentrations increased slightly in response to all three treatments, but not in a dose-dependent manner, and the timing of peak concentrations varied between doses. However, 15alpha-P plasma concentrations showed a greater range of response (between 1 and 100 ng/ml) and were clearly correlated with the injection dose. Plasma concentrations of 15alpha-P also responded to far lower doses of GnRH I and GnRH III than any other steroid previously investigated in lampreys. The plasma concentrations of 15alpha-P peaked at 6h after injection for all three treatments, and levels reached a mean of 53.1 ng/ml. In female lampreys that were injected twice with 50 microg/ml GnRH I or III, 15alpha-T concentrations did not exceed 0.5 ng/ml and 15alpha-P concentrations did not exceed 1 ng/ml. These results lend further support to the hypothesis that 15alpha-P plays an important role in the reproductive endocrinology of male lampreys.

Patterns of proopiomelanotropin and proopiocortin gene expression and of immunohistochemistry for gonadotropin-releasing hormones (lGnRH-I and III) during the life cycle of a nonparasitic lamprey: relationship to this adult life history type

There are two adult life history types among lamprey species, nonparasitic and parasitic, with the former commencing the final interval of sexual maturation immediately after metamorphosis. There are no extensive studies that directly compare hormone profiles during the life cycles of nonparasitic and parasitic lamprey species, yet such data may explain differences in development, reproductive maturation, and feeding status. The present study uses immunohistochemistry to show the life cycle profiles for gonadotropin-releasing hormones (GnRH-I and -III) in the brain of the nonparasitic species, the American brook lamprey, Lampetra appendix, for comparison with the extensive, published, immunohistochemical data on these hormones in the parasitic species, the sea lamprey, Petromyzon marinus. The complete cDNAs for the two lamprey prohormones, proopiocortin (POC), and proopiomelanotropin (POM), were cloned for L. appendix and both nucleotide and deduced amino acid sequences were compared with those previously published for P. marinus. The POC and POM cDNAs for both species were used in expression studies, with Northern blotting, throughout their life cycles. Although GnRH-I and -III immunohistochemistry revealed a similar distribution of immunoreactive cells and fibers in the two species during the life cycles, a qualitative evaluation of staining intensity in L. appendix, implied early activity in the brains of metamorphosis of this species, particularly in GnRH-I. GnRH-III seems to be important in larval life and early metamorphosis in both species. A novel feature of this immunohistochemical study is the monthly observations of the distribution and relative intensity of the two GnRHs during the critical period of final sexual maturation that lead to spawning and then the spent animal. L. appendix POC and POM nucleotide sequences had 92.9 and 94.6% identity, respectively, with P. marinus POC and POM and there was an earlier increase in their expression during metamorphosis and postmetamorphic life. Since there was some correlation between the timing of metamorphic development, gonad maturation, and brain irGnRH intensity with POC and POM expression in L. appendix, it was concluded that these prohormones yield posttranslational products that likely play a substantial role in development and maturation events that lead to the nonparasitic adult life history of this species.

Evolution of GnRH ligands and receptors in gnathostomata

Gonadotropin-releasing hormone (GnRH) is the final common signaling molecule used by the brain to regulate reproduction in all vertebrates. Until now, a total of 24 GnRH structural variants have been characterized from vertebrate, protochordate and invertebrate nervous tissue. Almost all vertebrates already investigated have at least two GnRH forms coexisting in the central nervous system. Furthermore, it is now well accepted that three GnRH forms are present both in early and late evolved teleostean fishes. The number and taxonomic distribution of the different GnRH variants also raise questions about the phylogenetic relationships between them. Most of the GnRH phylogenetic analyses are in agreement with the widely accepted idea that the GnRH family can be divided into three main groups. However, the examination of the gnathostome GnRH phylogenetic relationships clearly shows the existence of two main paralogous GnRH lineages: the ''midbrain GnRH" group and the "forebrain GnRH" group. The first one, represented by chicken GnRH-II forms, and the second one composed of two paralogous lineages, the salmon GnRH cluster (only represented in teleostean fish species) and the hypophysotropic GnRH cluster, also present in tetrapods. This analysis suggests that the two forebrain clades share a common precursor and reinforces the idea that the salmon GnRH branch has originated from a duplication of the hypophysotropic lineage. GnRH ligands exert their activity through G protein-coupled receptors of the rhodopsin-like family. As with the ligands, multiple GnRHRs are expressed in individual vertebrate species and phylogenetic analyses have revealed that all vertebrate GnRHRs cluster into three main receptor types. However, new data and a new phylogenetic analysis propose a two GnRHR type model, in which different rounds of gene duplications may have occurred in different groups within each lineage.

Expression of Neuropeptide Y Family Peptides in the Brain and Gut during Stages of the Life Cycle of a Parasitic Lamprey (Petromyzon marinus) and a Nonparasitic Lamprey (Ichthyomyzon gagei)

The long-term objective of our research is to show that internal factors may be key to triggering metamorphosis and directing the life history types in lampreys (parasitism versus nonparasitism). Since neuropeptide Y family peptides are key players in the endocrine-mediated feeding and reproductive events in mammals, a role for these peptides in the control of feeding behavior and development can be predicted for lampreys. We have investigated the expression pattern of these peptides in the brain and in the gut during different stages of the life cycle of the parasitic lamprey, Petromyzon marinus, and the nonparasitic lamprey, Ichthyomyzon gagei. We provide a description of the cloning and sequencing of P. marinus and I. gagei cDNA for neuropeptide Y (NPY), peptide tyrosine-tyrosine (PYY), and peptide methionine-tyrosine (PMY). Using sequence-specific primers, the mRNA expression patterns for these peptides in brain and gut of larval (ammocoete) and adult (juvenile, prespawning) lampreys were examined by semiquantitative RT-PCR. The observations extend a potential role of neuropeptide Y family peptides in the modulation of feeding behavior and reproductive maturity in lampreys.

Distribution of immunoreactive adenohypophysial cell types in the pituitaries of the Atlantic and the Pacific hagfish, Myxine glutinosa and Eptatretus burgeri

The hagfish is considered the most primitive vertebrate known, living or extinct. It remains an enigma whether adenohypophysial hormones similar to those of more advanced vertebrates are present in the hagfish pituitary gland or not. The present study aimed to detect immunoreactive adenohypophysial hormones in the hagfish pituitary gland, using antisera to tetrapod and fish adenohypophysial hormones as immunohistochemical probes. For this purpose, two species of hagfish, the Atlantic hagfish, Myxine glutinosa, and the Pacific hagfish, Eptatretus burgeri, were used. In both species, three different types of immunoreactive cells were detected in the adenohypophysis. (1) The first type of cells was gonadotropin (GTH)-like cells which were stained by antisera to LH-related GTHs, such as ovine LHbeta, human LHbeta, bullfrog LH, salmon LHbeta and sturgeon LHbeta in both species of hagfish. (2) The second type of cells that were detected was growth hormone (GH)/prolactin (PRL)-like cells. In M. glutinosa the cells were stained by antisera to salmon GH, salmon PRL, sturgeon GH, sturgeon PRL, blue shark GH, and lamprey GH. In E. burgeri the cells were only stained by anti-human GH and anti-sturgeon PRL. (3) The last type of cells was adrenocorticotropin (ACTH)-like cells. These cells were stained by antisera to lamprey ACTH and human beta-endorphin. In both species of hagfish, GTH-like cells were relatively abundant, and were distributed throughout the adenohypophysis, whereas GH/PRL-like and ACTH-like cells were few in number in the adenohypophysis. Based on these findings, we suggest that hagfish may have retained ancestral characteristics of key anterior pituitary hormones.

In vitro and in vivo effects of GABA, muscimol, and bicuculline on lamprey GnRH concentration in the brain of the sea lamprey (Petromyzon marinus)

gamma-Aminobutyric acid (GABA) is a neurotransmitter with a demonstrated neuroregulatory role in reproduction in most representative species of vertebrate classes via the hypothalamus. The role of GABA on the hypothalamus-pituitary axis in lampreys has not been fully elucidated. Recent immunocytochemical and in situ hybridization studies suggest that there may be a neuroregulatory role of GABA on the gonadotropin-releasing hormone (GnRH) system in lampreys. To assess possible GABA-GnRH interactions, the effects of GABA and its analogs on lamprey GnRH in vitro and in vivo were studied in adult female sea lampreys (Petromyzon marinus). In vitro perfusion of GABA and its analogs at increasing concentrations (0.1-100 microM) was performed over a 3-h time course. There was a substantial increase of GnRH-I and GnRH-III following treatment of muscimol at 100 microM. In in vivo studies, GABA or muscimol injected at 200 microg/kg significantly increased lamprey GnRH concentration in the brain 0.5 h after treatment compared to controls in female sea lampreys. No significant change in lamprey GnRH-I or GnRH-III was observed following treatment with bicuculline. These data provide novel physiological data supporting the hypothesis that GABA may influence GnRH in the brain of sea lamprey.

Seasonal changes of gonadotropin-releasing hormone in the Atlantic hagfish Myxine glutinosa

To investigate seasonal reproduction in Myxine glutinosa, we measured total brain gonadotropin-releasing hormone (GnRH) and determined gonadal stages of hagfish collected from the Gulf of Maine once a month for 12 months. Thirty hagfish from each of three different size classes of small (20-35 cm), medium (35-45 cm), and large (50-60+ cm) were sampled for brains and gonads. In the medium and large class hagfish there was an increase in GnRH concentrations during April and May that correlated with male and female gonadal maturity. Also in these size classes of female hagfish, there was a similar rise in GnRH in November and then again in January that preceded the highest incidence of large eggs (stage 7). The elevated GnRH may be influencing the onset of ovarian recrudescence which has been shown in other vertebrates. These data suggest an association of the concentration of brain GnRH with gonadal maturity and provide supportive evidence of a possible seasonal reproductive cycle in M. glutinosa shown in recent studies of [J. Exp. Zool. 301A (2004) 352], correlating steroid production with gonadal maturation.

Role of neuropeptide Y in the regulation of gonadotropin releasing hormone system in the forebrain of Clarias batrachus (Linn.): Immunocytochemistry and high performance liquid chromatography-electrospray ionization-mass spectrometric analysis

Although the importance of neuropeptide Y (NPY) in the regulation of gonadotropin releasing hormone (GnRH) and reproduction has been highlighted in recent years, the neuroanatomical substrate within which these substances might interact has not been fully elucidated. Present work was undertaken with a view to define the anatomical-physiological correlates underlying the role exercised by NPY in the regulation of GnRH in the forebrain of the teleost Clarias batrachus. Application of double immunocytochemistry revealed close associations as well as colocalizations of the two peptides in the olfactory receptor neurons (ORNs), olfactory nerve fibers and their terminals in the glomeruli, ganglion cells of nervus terminalis, medial olfactory tract, fibers in the area ventralis telencephali/pars supracommissuralis and cells as well as fibers in the pituitary. NPY containing axons were found to terminate in the vicinity of GnRH cells in the pituitary with light as well as electron microscopy. Double immunoelectron microscopy demonstrated gold particles for NPY and GnRH colocalized on the membrane and in dense core of the secretory granules in the cells distributed in all components of the pituitary gland. To assess the physiological implication of these observations, NPY was injected via the intracranial route and the response of GnRH immunoreactive system was evaluated by relative quantitative morphometry as well as high performance liquid chromatography (HPLC) analysis. Two hours following NPY (20 ng/g body weight) administration, a dramatic increase was observed in the GnRH immunoreactivity in the ORNs, in the fibers of the olfactory bulb (163%) and medial olfactory tract (351%). High performance liquid chromatography-electrospray ionization-mass spectrometric analysis confirmed the immunocytochemical data. Significant rise in the salmon GnRH (sGnRH)-like peptide content was observed in the olfactory organ (194.23%), olfactory bulb (146.64%), telencephalon+preoptic area (214.10%) and the pituitary (136.72%) of the NPY-treated fish. However, GnRH in the hypothalamus was below detection limit in the control as well as NPY-treated fish. Present results suggest the involvement of NPY in the up-regulation of sGnRH containing system at different level of neuraxis extending from the olfactory epithelium to the pituitary in the forebrain of C. batrachus.

Cloning and analysis of the lamprey GnRH-III cDNA from eight species of lamprey representing the three families of Petromyzoniformes

The lamprey, which are divided into three families, including the Petromyzonidae, Geotriidae, and Mordaciidae, have been shown to regulate the reproductive axis through a functional hypothalamic-pituitary-gonadal axis. To date, two forms of gonadotropin-releasing hormone (GnRH) have been identified in the sea lamprey (Petromyzon marinus), lamprey GnRH-I (decapeptide and cDNA) and lamprey GnRH-III (decapeptide), both of which have been shown to be expressed in the preoptic-anterior hypothalamic region and both forms have been demonstrated to regulate reproductive function (i.e. steroidogenesis and gametogenesis). The objective of this study was to isolate the cDNA encoding the prepro-lamprey GnRH-III from eight species of lamprey using a PCR based subcloning procedure. A degenerate primer designed to the lamprey GnRH-III decapeptide was used to amplify the 3' end of each transcript, while gene specific primers were used to amplify the 5' ends. Phylogenetic analysis using the prepro-lamprey GnRH-III amino acid sequences was performed, in which the lamprey GnRH-III sequences divided into three groups, supporting the current view of the lamprey lineage at the family level. Finally, a phylogenetic analysis of these newly identified deduced amino acid sequences together with 64 previously described GnRH sequences suggests that the lamprey GnRHs are unique, as they group together separately from the three previously described paralogous lineages of the GnRH family.

Novel fish-derived adrenomedullin in mammals: structure and possible function

Adrenomedullin (AM) has been recognized as a member of the calcitonin (CT)/CT gene-related peptide (CGRP) family. However, an independent AM family consisting of five paralogous peptides exists in teleost fish. Among them, the peptide named AM1 is an ortholog of mammalian AM as determined by the linkage analysis of orthologous genes and the presence of proAM N-terminal 20 peptide (PAMP)-like sequence in the prosegment. Since the peptides named AM2 and 3 are distinct from other members with respect to the precursor sequence, tissue distribution of the transcripts, and exon-intron organization, we searched for their mammalian orthologs from genome databases, which resulted in an identification of AM2 in human, rat, and mouse. AM2 was expressed abundantly in the submaxillary gland, kidney, and some vascular and digestive tissues of mice. AM2 injected in vivo induced potent cardiovascular and renal effects in mice. In the heart and kidney of mice, AM2 was localized in endothelial cells of the coronary vessels and in glomeruli and vasa recta, respectively. AM2 increased cAMP accumulation in cells expressing human CT receptor-like receptor (CRLR) and one of receptor activity-modifying proteins (RAMPs), but it was no more potent than CGRP and AM. AM2 was also less potent than CT in cells expressing CT receptor and RAMP. There remains a possibility that a new AM2-specific receptor or an additional RAMP that enables CRLR to be an AM2-specific receptor, exists in mammals.

Reelin immunoreactivity in the adult sea lamprey brain

The expression of reelin, a large extracellular matrix glycoprotein, was studied in the brain of pre-spawning adult sea lampreys by immunohistochemistry using two monoclonal antibodies against this protein. Reelin immunoreactive (reln-ir) neurons were observed in the olfactory bulb, and pallial and subpallial regions in the telencephalon. In the diencephalon, reln-ir cells were observed in some hypothalamic nuclei, in the nucleus of Bellonci, and in the habenula. In the mesencephalon, this protein was detected in several nuclei related with the centrifugal visual system, although the optic tectum was devoid of immunoreactivity. The hindbrain showed several nuclei with immunopositive neurons, including the branchiomeric nerve motor nuclei and also some groups of non-giant cells of the reticular formation. The rostral spinal cord showed some immunopositive neurons mainly located in lateral and ventral positions. Overall, the pattern of distribution of reelin in the adult sea lamprey correlates with the previously reported in other adult vertebrates. Furthermore, the wide distribution of reelin in the adult lamprey brain is consistent with a possible existence of different roles for this protein not related with development in the central nervous system (CNS) of vertebrates (i.e. neuronal plasticity and/or maintenance).

15alpha-hydroxytestosterone induction by GnRH I and GnRH III in Atlantic and Great Lakes sea lamprey (Petromyzon marinus L.)

The sea lamprey (Petromyzon marinus L.) represents one of the two most ancient classes of vertebrates and possesses a functional hypothalamus-pituitary-gonadal axis. However, the presence and functionality of androgens in the sea lamprey remain elusive. Recently, 15alpha-hydroxytestosterone (15alpha-T) has been found in sea lamprey gonads and blood plasma. In this study we examined changes of circulatory concentrations of 15alpha-T in response to gonadotropin releasing hormone (GnRH) treatments. Plasma concentrations of 15alpha-T in sea lamprey increased 2-5 times for all GnRH-injected sea lamprey compared to controls (P < 0.001). However, there were no differences among responses: (1) to the two forms of GnRH (lamprey GnRH I or lamprey GnRH III), (2) to the doses delivered (50, 100, or 200 microg/kg), or (3) between post-injection sample intervals (8 or 24 h). Between lampreys from the Atlantic Ocean and Great Lakes sites, two of seven GnRH form and dosage comparisons showed between-site differences, but were not believed to represent an overall between-site difference. These are the first data to show a response of a C19 steroid to GnRH stimulation in sea lamprey.

Development of the adenohypophysis in the lamprey: evolution of epigenetic patterning programs in organogenesis

In gnathostomes, the adenohypophysis, a component of the hypothalamo-hypophysial complex, is believed to develop through hierarchically organized epigenetic interactions based primarily on the topographical relationships between tissues. From a comparison of developmental processes and gene expression patterns of pituitary-related genes between the agnathan species, lampreys and gnathostomes, we speculate on the evolutionary pathway of the vertebrate adenohypophysis. In the lamprey, this is derived from the nasohypophysial placode (NHP) that develops anterior to the oral ectoderm. The NHP can be identified by the expression of LjPitxA, before actual histogenesis, but it is initially distant from the future hypothalamic region. Subsequently, the NHP expresses both LjFgf8/17 and LjBmp2/4a gene transcripts, and grows caudally to establish a de novo contact with the hypothalamic region by the mid-pharyngula stage. Later, the NHP gives rise to both the adenohypophysis and an unpaired nasal organ. Thus, the topographical relationship between the NHP and the hypothalamic region is established secondarily in the lamprey, unlike gnathostomes in which the equivalent relationship appears early in development. Comparing the developmental pattern of the amphioxus homologue of the adenohypophysis, we hypothesize that a modification of the regulation of the growth factor encoding gene lies behind the evolutionary changes recognized as heterochrony and heterotopy, which leads to the gnathostome hypophysial developmental pattern.

15 alpha-Hydroxytestosterone produced in vitro and in vivo in the sea lamprey, Petromyzon marinus

Prior research has shown that the testes of lampreys are able to synthesize 15-hydroxylated steroid hormones in vitro. Here we show that testes of the sea lamprey Petromyzon marinus L. are able to convert tritiated testosterone into tritiated 15alpha-hydroxytestosterone (15alpha-T) in high yield. The identity of the tritiated 15alpha-T has been confirmed by: co-elution with standard 15alpha-T on high performance liquid chromatography (HPLC); co-elution on thin layer chromatography (TLC); co-elution of acetylated tritiated and standard 15alpha-T on TLC; and strong binding to an antiserum developed against 15alpha-T. The strong reaction between the tritiated 15alpha-T and the antiserum has been used to develop a radioimmunoassay (RIA). The RIA operates over the range of 500-2pg per tube; and can be applied directly to plasma samples. This assay has been used to demonstrate that 15alpha-T is present in blood plasma of the sea lamprey. The concentrations of 15alpha-T in captive lamprey were found to be as follows (pg/ml; mean+/-SEM, n): parasitic stage (reproductively immature), <20, n=7; pre-ovulatory females, 156+/-30, n=8; ovulated females, 62+/-9, n=5; pre-spermiating males, 275+/-19, n=8; spermiating males, 216+/-48, n=8. When spermiating male plasma was fractionated on HPLC, immunoreactivity was found exclusively in the expected elution position of 15alpha-T. The biological significance of this steroid has yet to be established.

Blood steroid profile and in vitro steroidogenesis by ovarian follicles and testis fragments of adult sea lamprey, Petromyzon marinus

The main purpose of the study was to identify the principal gonadal steroids synthesized by male and female sea lampreys, Petromyzon marinus. To achieve this, we used high performance liquid chromatography to separate the steroids in the serum of sexually mature animals, and to separate the steroids produced by gonadal tissue incubated in the presence of radiolabelled precursor steroids, as a means of identifying the major steroidogenic pathways. We were unable to detect evidence of the 'classical' steroids, such as 17beta-estradiol (E(2)) or testosterone (T) in the serum of either male or female lampreys. Instead, the principal chromatographic peaks contained very polar compounds that had elution times consistent with 15alpha-hydroxylated estrogens and androgens, and there were sex-specific differences in the chemical nature and the quantity of these compounds. Testis fragments or ovarian follicles co-incubated with tritium-labelled pregnenolone ([3H]P(5)), 17-hydroxyprogesterone ([3H]17OHP(4)), or androstenedione ([3H]A(4)), provided additional confirmation that the gonads synthesize a range of very polar steroids, and the metabolites found were consistent with the presence of a 15alpha-hydroxylated (15alphaOH) metabolic pathway common to testis and ovary. For ovarian tissue, the major 'end product' metabolites from all three precursors were 15alphaOH-estrogens, and for testis tissue 15alpha-hydroxyprogesterone (15alphaOHP(4)) and 15alpha-hydroxytestosterone (15alphaOHT) and small amounts of 15alphaOH estrogen. Small amounts of E(2) were also produced by both ovarian (all substrates) and testicular tissue (some substrates). Although it was assumed that the E(2) was synthesized via the aromatization of T, [3H]T was not found as an intermediate metabolite. The study suggests that the principal gonadal steroids in sea lamprey are 15alpha-OH compounds, and that only small amounts of E(2) or T are synthesized by the gonads at this stage of reproductive development. There was no direct evidence of progesterone (P(4)) synthesis from [3H]P(5), although the metabolites synthesized by both testis and ovary were indicative of a metabolic pathway that involved P(4) as an intermediate.

Gonadotropin-releasing hormone (GnRH): from fish to mammalian brains

This work deals with a family of neuropeptides, gonadotropin-releasing hormone (GnRH), that play a key role in the development and maintenance of reproductive function in vertebrates. 2. Until now, a total of 16 GnRH structural variants have been isolated and characterized from vertebrate and protochordate nervous tissue. All vertebrate species already investigated have at least two GnRH forms coexisting in the central nervous system. However, it is now well accepted that three forms of GnRH in early and late evolved bony fishes are present. 3. In these cases, cGnRH-II is expressed by midbrain neurons, a species-specific GnRH is present mainly in the preoptic area and the hypothalamus, and sGnRH is localized in the terminal nerve ganglion (TNG). In this context it is possible to think that three GnRH forms and three GnRH receptor (GnRH-R) subtypes are expressed in the central nervous system of a given species. 4. Then it is possible to propose three different GnRH lineages expressed by distinct brain areas in vertebrates: (1) the conserved cGnRH-II or mesencephalic lineage; or (2) the hypothalamic or "releasing" lineage whose primary structure has diverged by point mutations (mGnRH and its orthologous forms: hrGnRH, wfGnRH, cfGnRH, sbGnRH, and pjGnRH); and (3) the telencephalic sGnRH form. Also different GnRH nomenclatures are discussed.