Evidence that 4-pregnen-17,20beta,21-triol-3-one functions as a maturation-inducing hormone and pheromonal precursor in the percid fish, Gymnocephalus cernuus

Cloning, localization and differential expression of Neuropeptide-Y during early brain development and gonadal recrudescence in the catfish, Clarias gariepinus

Neuropeptide-Y (NPY) has diverse physiological functions which are extensively studied in vertebrates. However, regulatory role of NPY in relation to brain ontogeny and recrudescence with reference to reproduction is less understood in fish. Present report for the first time evaluated the significance of NPY by transient esiRNA silencing and also analyzed its expression during brain development and gonadal recrudescence in the catfish, Clarias gariepinus. As a first step, full-length cDNA of NPY was cloned from adult catfish brain, which shared high homology with its counterparts from other teleosts upon phylogenetic analysis. Tissue distribution revealed dominant expression of NPY in brain and testis. NPY expression increased during brain development wherein the levels were higher in 100 and 150days post hatch females than the respective age-matched males. Seasonal cycle analysis showed high expression of NPY in brain during pre-spawning phase in comparison with other reproductive phases. Localization studies exhibited the presence of NPY, abundantly, in the regions of preoptic area, hypothalamus and pituitary. Transient silencing of NPY-esiRNA directly into the brain significantly decreased NPY expression in both the male and female brain of catfish which further resulted in significant decrease of transcripts of tryptophan hydroxylase 2, catfish gonadotropin-releasing hormone (cfGnRH), tyrosine hydroxylase and 3β-hydroxysteroid dehydrogenase in brain and luteinizing hormone-β/gonadotropin-II (lh-β/GTH-II) in pituitary exhibiting its influence on gonadal axis. In addition, significant decrease of several ovary-related transcripts was observed in NPY-esiRNA silenced female catfish, indicating the plausible role of NPY in ovary through cfGnRH-GTH axis.

Transcriptional signature of progesterone in the fathead minnow ovary (Pimephales promelas)

A growing number of studies have examined transcriptional responses to sex steroids along the hypothalamic-pituitary-gonadal axis in teleost fishes. However, data are lacking on the molecular cascades that underlie progesterone signaling. The objective of this study was to characterize the transcriptional response in the ovary of fathead minnows (Pimephales promelas) in response to progesterone (P4). Fathead minnow ovaries were exposed in vitro to 500 ng P4/L. Germinal vesicle migration and breakdown (GVBD) was observed and microarrays were used to identify gene cascades affected by P4. Microarray analysis identified 1702 differentially expressed transcripts after P4 treatment. Functional enrichment analysis revealed that transcripts involved in the molecular functions of protein serine/threonine kinase activity, ATP binding, and activity of calcium channels were increased after P4 treatment. There was an overwhelming decrease in levels of transcripts of genes that are structural constituents of ribosomes with P4 treatment. There was also evidence for gene expression changes in steroid and maturation-related transcripts. Pathway analyses identified cell cycle regulation, insulin action, hedgehog, and B cell activation as pathways containing an over-representation of highly regulated transcripts. Significant regulatory sub-networks of P4-mediated transcripts included genes regulated by tumor protein p53 and E2F transcription factor 1. These data provide novel insight into the molecular signaling cascades that underlie P4-signaling in the ovary and identify genes and processes that may indicate premature GVBD due to environmental pollutants that mimic progestins.

Chemical analysis of aquatic pheromones in fish

Pheromones are chemicals that pass between members of the same species that have inherent meaning. In the case of fish, pheromones are water-soluble and found in low concentrations. As such, sensitive and selective methods are needed to separate and analyze these pheromones from an environmental matrix that may contain many other chemicals. This chapter describes a generic method used to concentrate and identify these chemicals and two extremely sensitive and selective methods for analysis, namely, mass spectrometry and enzyme-linked immunosorbent assay.

Discovery of a novel enzyme mediating glucocorticoid catabolism in fish: 20beta-hydroxysteroid dehydrogenase type 2

Hydroxysteroid dehydrogenases (HSDs) are involved in metabolism and pre-receptor regulation of steroid hormones. While 17beta-HSDs and 11beta-HSDs are extensively studied in mammals, only few orthologs are characterized in fish. We discovered a novel zebrafish HSD candidate closely related to 17beta-HSD types 3 and 12, which has orthologs in other species. The enzyme catalyzes the conversion of cortisone to 20beta-hydroxycortisone identified by LC-MS/MS. We named the new enzyme 20beta-HSD type 2. All 20beta-HSD type 2 orthologs localize in the endoplasmic reticulum. Zebrafish 20beta-HSD type 2 is expressed during embryonic development showing the same expression pattern as 11beta-HSD type 2 known to oxidize cortisol to cortisone. In adult tissues 20beta-HSD type 2 shows a ubiquitous expression pattern with some minor sex-specific differences. In contrast to other enzymes metabolizing C21-steroids and being mostly involved in reproduction we propose that novel type 2 20beta-HSDs in teleost fish are important enzymes in cortisol catabolism.

The role of the maturation-inducing steroid, 17,20beta-dihydroxypregn-4-en-3-one, in male fishes: a review

The major progestin in teleosts is not progesterone, as in tetrapods, but 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or, in certain species, 17,20beta,21-trihydroxy-pregn-4-en-3-one (17,20beta,21-P). Several functions for 17,20beta-P and 17,20beta,21-P have been proposed (and in some cases proved). These include induction of oocyte final maturation and spermiation (milt production), enhancement of sperm motility (by alteration of the pH and fluidity of the seminal fluid) and acting as a pheromone in male cyprinids. Another important function, initiation of meiosis (the first step in both spermatogenesis and oogenesis), has only very recently been proposed. This is a process that takes place at puberty in all fishes and once a year in repeat spawners. The present review critically examines the evidence to support the proposed functions of 17,20beta-P in males, including listing of the evidence for the presence of 17,20beta-P in the blood plasma of male fishes and discussion of why, in many species, it appears to be absent (or present at low and, in some cases, unvarying concentrations); consideration of the evidence, obtained mainly from in vitro studies, for this steroid being predominantly produced by the testis, for its production being under the control of luteinizing hormone (gonadotrophin II) and, at least in salmonids, for two cell types (Leydig cells and sperm cells) being involved in its synthesis; discussion of the factors involved in the regulation of the switch from androgen to 17,20beta-P production that seems to occur in many species just at the time of spermiation; discussion of the effects of in vivo injection and application of 17,20beta-P (and closely related compounds) in males; a listing of previously published evidence that supports the proposed new function of 17,20beta-P as an initiator of meiosis; finally, discussion of the evidence for environmental endocrine disruption by progestins in fishes.

Expression and gonadotropin regulation of membrane progestin receptor alpha in Atlantic croaker (Micropogonias undulatus) gonads: role in gamete maturation

Recent results suggest that membrane progestin receptor alpha (mPRalpha) mediates nongenomic actions of progestin hormones to induce oocyte maturation and sperm hypermotility in several teleost species. The role of mPRalpha in gamete and gonadal physiology was further evaluated in the present study by examining gonadal expression of mPRalpha during gamete maturation in Atlantic croaker (Micropogonias undulatus), a well-characterized teleost model of oocyte maturation and sperm motility. Sequencing of the croaker mPRalpha gene isolated from croaker ovaries showed it is 98% homologous at the nucleotide level to spotted seatrout mPRalpha. The mPRalpha mRNA and protein were detected in both somatic and gonadal tissues. In croaker ovaries, the mPRalpha protein was present throughout the gonadal cycle and was upregulated by gonadotropin in vitro, coincident with the acquisition of oocyte maturational competence (i.e., ability to respond to progestin hormones and complete oocyte maturation). Both mPRalpha mRNA and protein were also expressed in croaker testes throughout the gonadal cycle. Expression of mPRalpha protein was weakly upregulated in testes after 18 h of in vitro gonadotropin treatment. Immunocytochemical staining showed mPRalpha was localized to both germ and interstitial cells. Finally, elevated levels of mPRalpha protein in croaker sperm were associated with high sperm motility. Taken together, these data strongly support the hypothesis that mPRalpha mediates progestin induction of oocyte maturation and upregulation of sperm motility in teleosts.

Progestin signaling through an olfactory G protein and membrane progestin receptor-alpha in Atlantic croaker sperm: potential role in induction of sperm hypermotility

Progestin stimulation of sperm hypermotility remains poorly understood despite having been described in numerous vertebrate species. We show here that progestin stimulation of sperm hypermotility in a teleost, the Atlantic croaker (Micropogonias undulatus) is associated with activation of an olfactory G protein (Golf). Furthermore, we provide evidence that this progestin action is mediated by membrane progestin receptor-alpha (mPRalpha). Golf was identified in croaker sperm membranes and was specifically activated after treatment with the progestin 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S). Treatment of sperm membranes with 20beta-S caused an increase in cAMP production, which was blocked by pretreatment with cholera toxin and two membrane adenylyl cyclase inhibitors: 2',5'-dideoxyadenosine and SQ22536. Moreover, preincubation of croaker sperm with 2',5'-dideoxyadenosine and SQ22536 resulted in a significant inhibition of 20beta-S-stimulated hypermotility. Binding of [3H]20beta-S to sperm membranes was decreased after pretreatment with GTPgammaS but not pertussis toxin, suggesting the receptor is coupled to a pertussis toxin-insensitive G protein. Golf and mPRalpha were coexpressed on the sperm midpiece and flagella and were coimmunoprecipitated from sperm membranes. Finally, expression of mPRalpha protein on sperm increased after in vivo treatment with LHRH and was associated with increased induction of sperm motility by 20beta-S. These results suggest that 20beta-S activates mPRalpha in croaker sperm, which in turn activates Golf and membrane adenylyl cyclase to stimulate sperm hypermotility. Taken together these findings provide a plausible mechanism by which progestins stimulate sperm hypermotility in croaker and provide the first evidence of hormonal activation of Golf in any species.

Olfactory sensory input increases gill ventilation in male round gobies (Neogobius melanostomus) during exposure to steroids

In teleostean fish, ventilation increases have been observed in response to low dissolved oxygen levels, visual stimuli, and gustatory cues. However, olfactory sensory input may also stimulate gill ventilation rate. We investigated whether olfactory sensory input mediates gill ventilation responses, as suggested by the observation that steroidal compounds detected by the olfactory system elicited increases in opercular activity in the perciform teleost, the round goby (Neogobius melanostomus). Close parallels between gill ventilation and olfactory responses, led us to conduct an empirical study that used two different olfactory sensory deprivation techniques to seek a causal relationship between olfactory epithelial activity and hyperventilation. Chemical lesion of olfactory sensory neurons or mechanical occlusion of the nasal cavities inhibited gill ventilation responses of reproductive male round gobies to estrone (1,3,5(10)-estratrien-3-ol-17-one) and to ovarian extracts. This direct evidence demonstrates the role of olfactory sensory input for the gill ventilation response to putative reproductive pheromones and may represent an important regulatory mechanism for odorant sampling during pheromone communication.