15Alpha-hydroxyprogesterone in male sea lampreys, Petromyzon marinus L

Sex-dependent pheromonal effects on steroid hormone levels in sea lampreys (Petromyzon marinus)

Sea lampreys (Petromyzon marinus) are basal vertebrates that exhibit reproductive control via a hypothalamic-pituitary-gonadal axis. The function and evolution of the hypothalamic and pituitary peptide hormones are well studied in this species, whereas the functions of classical sex steroid hormones have not been well established due to their low or non-detectable plasma levels. Sea lamprey pheromone 3-keto petromyzonol sulfate (3kPZS) has been shown to increase while 3-keto allocholic acid (3kACA) decreases plasma 15α-hydroxyprogesterone (15αP) levels in prespermiating males (PSM) but not in preovulatory females (POF). However, spermiating male washings that contain both 3kPZS and 3kACA facilitate spawning in both sexes. Therefore, we wondered if the effects of pheromones on POF were elicited by classical steroid hormones such as progesterone, androstenedione, testosterone and estradiol. We hypothesized that waterborne 3kACA and 3kPZS differentially alter steroid hormone levels in prespawning sea lampreys. We determined the sex differences and pheromonal effects on steroid hormone levels in prespawning sea lampreys using sensitive ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) methods. Some PSM became spermiating (SM) at the time of sample collection, and those data were treated as a separate group. We found that males contained more androstenedione and progesterone in the gonad and more estradiol and testosterone in the plasma than POF, whereas POF contained more gonadal testosterone than males (no detectable gonadal testosterone). In POF, 3kPZS decreased gonadal androstenedione but increased gonadal progesterone and plasma estradiol, whereas 3kACA only increased gonadal progesterone levels. Exposure to 3kPZS for 4 h increased plasma 15αP in POF and SM, and gonadal 15αP in POF. Interestingly, 3kACA or 3kPZS depleted gonadal or plasma 15αP in PSM at various time points. On the other hand, both pheromones had no significant effect on androstenedione, progesterone or estradiol levels in males. Plasma testosterone levels did not change after pheromone exposure in both sexes. We conclude that sea lamprey pheromones 3kACA and 3kPZS induced differential steroidal responses in POF, PSM and SM.

Evidence that progestins play an important role in spermiation and pheromone production in male sea lamprey (Petromyzon marinus)

Progestins (progestogens, C21 steroids) have been shown to regulate key physiological activities for reproduction in both sexes in all classes of vertebrates except for Agnathans. Progesterone (P) and 15α-hydroxyprogesterone (15α-P) have been detected in sea lamprey (Petromyzon marinus) plasma, but the expression patterns and functions of putative progestin receptor genes have not yet been investigated. The first objective of this study was to determine the differences in mRNA expression levels of nuclear progestin receptor (nPR) and the membrane receptor adaptor protein 'progesterone receptor membrane component 1' (pgrmc1) in putative target tissues in males at different life stages, with and without lamprey GnRH-I and -III treatment. The second objective was to demonstrate the function of progestins by implanting prespermiating males (PSM) with time-release pellets of P and measuring the latency to the onset of spermiation and plasma concentrations of sex pheromones and steroids. The third objective was to measure the binding affinity of P in the nuclear and membrane fractions of the target tissues. Expression levels of nPR and pgrmc1 differed between life stages and tissues, and in some cases were differentially responsive to lamprey GnRH-I and -III. Increases in nPR and pgrmc1 gene expressions were correlated to the late stages of sexual maturation in males. The highest expression levels of these genes were found in the liver and gill of spermiating males. These organs are, respectively, the site of production and release of the sex pheromone 3 keto-petromyzonol sulfate (3kPZS). The hypothesis that pheromone production may be under hormonal control was tested in vivo by implanting PSM with time-release pellets of P. Concentrations of 3kPZS in plasma after 1week were 50-fold higher than in controls or in males that had been implanted with androstenedione, supporting the hypothesis that P is responsible for regulating the production of the sex pheromone. P treatment also accelerated the onset of spermiation. Saturation and Scatchard analyses of the target tissues showed that both nuclear and membrane fractions bound P with high affinity and low capacity (KD 0.53pmol/g testis and 0.22 pmol/g testis, and Bmax 1.8 and 5.7 nM, respectively), similar to the characteristics of nPR and mPR in other fish. The fact that a high proportion of P was also converted in vivo to 15α-P means that it is not yet possible to determine which of these two steroids is the natural ligand in the sea lamprey.

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.

Regulation of a putative corticosteroid, 17,21-dihydroxypregn-4-ene,3,20-one, in sea lamprey, Petromyzon marinus

In higher vertebrates, in response to stress, the hypothalamus produces corticotropin-releasing hormone (CRH), which stimulates cells in the anterior pituitary to produce adrenocorticotropic hormone (ACTH), which in turn stimulates production of either cortisol (F) or corticosterone (B) by the adrenal tissues. In lampreys, however, neither of these steroids is present. Instead, it has been proposed that the stress steroid is actually 17,21-dihydroxypregn-4-ene-3,20-dione (11-deoxycortisol; S). However, there have been no studies yet to determine its mechanism of regulation or site of production. Here we demonstrate that (1) intraperitoneal injections of lamprey-CRH increase plasma S in a dose dependent manner, (2) intraperitoneal injections of four lamprey-specific ACTH peptides at 100μg/kg, did not induce changes in plasma S concentrations in either males or females; (3) two lamprey-specific gonadotropin-releasing hormones (GnRH I and III) and arginine-vasotocin (AVT), all at single doses, stimulated S production as well as, or to an even greater extent than CRH; (4) sea lamprey mesonephric kidneys, in vitro, converted tritiated 17α-hydroxyprogesterone (17α-P) into a steroid that had the same chromatographic properties (on HPLC and TLC) as S; (5) kidney tissues released significantly more immunoassayable S into the incubation medium than gill, liver or gonad tissues. One interpretation of these results is that the corticosteroid production of the sea lamprey, one of the oldest extant vertebrates, is regulated through multiple pathways rather than the classical HPI-axis. However, the responsiveness of this steroid to the GnRH peptides means that a reproductive rather than a stress role for this steroid cannot yet be ruled out.

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.

Do mollusks use vertebrate sex steroids as reproductive hormones? Part I: Critical appraisal of the evidence for the presence, biosynthesis and uptake of steroids

The consensus view is that vertebrate-type steroids are present in mollusks and perform hormonal roles which are similar to those that they play in vertebrates. Although vertebrate steroids can be measured in molluscan tissues, a key question is 'Are they formed endogenously or they are picked up from their environment?'. The present review concludes that there is no convincing evidence for biosynthesis of vertebrate steroids by mollusks. Furthermore, the 'mollusk' genome does not contain the genes for key enzymes that are necessary to transform cholesterol in progressive steps into vertebrate-type steroids; nor does the mollusk genome contain genes for functioning classical nuclear steroid receptors. On the other hand, there is very strong evidence that mollusks are able to absorb vertebrate steroids from the environment; and are able to store some of them (by conjugating them to fatty acids) for weeks to months. It is notable that the three steroids that have been proposed as functional hormones in mollusks (i.e. progesterone, testosterone and 17β-estradiol) are the same as those of humans. Since humans (and indeed all vertebrates) continuously excrete steroids not just via urine and feces, but via their body surface (and, in fish, via the gills), it is impossible to rule out contamination as the sole reason for the presence of vertebrate steroids in mollusks (even in animals kept under supposedly 'clean laboratory conditions'). Essentially, the presence of vertebrate steroids in mollusks cannot be taken as reliable evidence of either endogenous biosynthesis or of an endocrine role.

Isolation and identification of petromyzestrosterol, a polyhydroxysteroid from sexually mature male sea lamprey (Petromyzon marinus L.)

Petromyzestrosterol (1), a novel polyhydroxylated steroid, was identified from water conditioned with sexually mature male sea lamprey (Petromyzon marinus), a jawless vertebrate animal. Along with this novel steroid, two known steroids, 7α,12α,24-trihydroxy-5α-cholan-3-one-24-sulfate (3k PZS) and 7α,12α,24-trihydroxy-5α-cholan-24-sulfate (PZS), were isolated. Structures of these compounds were unequivocally established by spectroscopic analyses and by comparison with spectra of known compounds. Electro-olfactogram recordings (EOG) showed that 1 at nanomolar concentrations was stimulatory for the olfactory epithelium of adult females. 3k PZS, known to function as a male sex pheromone, was more stimulatory than 1 for the female olfactory epithelia. The concentration-response curve of 3k PZS was exponential in shape with steep slopes between 10(-10) and 10(-6) mol L(-1). The concentration-response curve for 1 was shallower than that for 3k PZS.

3D models of lamprey progesterone receptor complexed with progesterone, 7α-hydroxy-progesterone and 15α-hydroxy-progesterone

Sea lamprey, a basal vertebrate, contains a progesterone receptor [PR]. An unusual property of lamprey is that gonadotropin-releasing hormone induces synthesis of 15α-hydroxy-progesterone [15α-OH-P] instead of progesterone. There also is indirect evidence for 7α-OH-P in lamprey serum. To determine if there is a structural basis for the binding of 7α-OH-P and 15α-OH-P to lamprey PR, we constructed 3D models of the lamprey PR complexed with progesterone, 7α-OH-P and 15α-OH-P. These 3D models reveal that Met-277 in lamprey PR has a specific interaction with the 15α-hydroxyl on 15α-OH-P and with Met-192, which also contacts the 15α-hydroxyl group. We also find that 7α-OH-P has favorable contacts with side-chains in lamprey PR. BLAST searches reveal that Met-277 on lamprey PR is unique among vertebrate PRs. This unique site on lamprey PR could be a target for compounds to control reproduction in sea lamprey, an environmental pest in Lake Michigan.

Annual sex steroid and other physiological profiles of Pacific lampreys (Entosphenus tridentatus)

We documented changes in plasma levels of estradiol 17-beta (E2), progesterone (P), 15alpha-hydroxytestosterone (15alpha-T), thyroxine (T4), triiodothyronine (T3), protein, triglycerides (TGs), and glucose in adult Pacific lampreys (Entosphenus tridentatus) held in the laboratory in two different years. Levels of E2 in both sexes ranged from 0.5 to 2 ng/mL from September to March, peaked in late April (2-4 ng/mL), and decreased in May, with levels higher in males than in females. Levels of P were low from September through April, but then increased substantially during May (2-4 ng/mL), with levels again highest in males. Levels of 15alpha-T in males were around 0.75 ng/mL through the winter before exceeding 1 ng/mL in April and decreasing thereafter, whereas females showed a gradual increase from 0.25 ng/mL in November to 0.5 ng/mL in April before decreasing. Thyroxine concentrations differed between fish in each year, with most having levels ranging from 0.75 to 2.5 ng/mL in the fall and winter, and only fish in 2003 showing distinct peaks (3-4 ng/mL) in early April or May. Plasma T3 was undetectable from November through mid-March before surging dramatically in April (ca. 150 ng/mL) and decreasing thereafter. Levels of protein, TGs, and glucose decreased or were stable during the fall and winter with TGs and glucose surging in late April to early May for some fish. Our study is the first to document long-term physiological changes in Pacific lampreys during overwintering and sexual maturation and increases our understanding of the life history of this unique fish.

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.

Structural analysis of the evolution of steroid specificity in the mineralocorticoid and glucocorticoid receptors

Background

The glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) evolved from a common ancestor. Still not completely understood is how specificity for glucocorticoids (e.g. cortisol) and mineralocorticoids (e.g. aldosterone) evolved in these receptors.

Results

Our analysis of several vertebrate GRs and MRs in the context of 3D structures of human GR and MR indicates that with the exception of skate GR, a cartilaginous fish, there is a deletion in all GRs, at the position corresponding to Ser-949 in human MR. This deletion occurs in a loop before helix 12, which contains the activation function 2 (AF2) domain, which binds coactivator proteins and influences transcriptional activity of steroids. Unexpectedly, we find that His-950 in human MR, which is conserved in the MR in chimpanzee, orangutan and macaque, is glutamine in all teleost and land vertebrate MRs, including New World monkeys and prosimians.

Conclusion

Evolution of differences in the responses of the GR and MR to corticosteroids involved deletion in the GR of a residue corresponding to Ser-949 in human MR. A mutation corresponding to His-950 in human MR may have been important in physiological changes associated with emergence of Old World monkeys from prosimians.

Comparison of synthesis of 15 alpha-hydroxylated steroids in males of four North American lamprey species

Recent studies have provided evidence that 15 alpha-hydroxytestosterone (15 alpha-T) and 15 alpha-hydroxyprogesterone (15 alpha-P) are produced in vitro and in vivo in adult male sea lampreys (Petromyzon marinus), and that circulatory levels increase in response to injections with gonadotropin-releasing hormone (GnRH). We examined four species from the Petromyzontidae family including silver lampreys (Ichthyomyzon unicuspis), chestnut lampreys (I. castaneus), American brook lampreys (Lethenteron appendix), and Pacific lampreys (Entosphenus tridentatus) to determine if these unusual steroids were unique to sea lampreys or a common feature in lamprey species. In vitro production was examined through incubations of testis with tritiated precursors, and 15 alpha-T and 15 alpha-P production was confirmed in all species through co-elution with standards on both high performance liquid chromatography (HPLC) and thin layer chromatography. In vivo production was proven by demonstrating that HPLC-fractionated plasma had peaks of immunoreactive 15 alpha-T and 15 alpha-P that co-eluted with standards through using previously developed radioimmunoassays for 15 alpha-T and 15 alpha-P. The possible functionality of 15 alpha-T and 15 alpha-P was further examined in silver and Pacific lampreys by investigating the effect of injection of either type of lamprey GnRH on plasma concentrations of 15 alpha-T and 15 alpha-P. Injections with exogenous GnRH did not affect circulatory levels of either steroid in silver lampreys, and only GnRH III elicited higher levels of both steroids in Pacific lampreys. The 15 alpha-hydroxylase enzyme(s) for steroids appeared to present in adult males of all species examined, but the question of whether 15 alpha-hydroxylated steroids are functional in these lamprey species, and the significance of the 15-hydroxyl group, requires further research.