"Brain sex differentiation" in teleosts: Emerging concepts with potential biomarkers

The expression profiles of cyp19a1, sf-1, esrs and gths in the brain-pituitary during gonadal sex differentiation in juvenile Japanese eels

Eels are gonochoristic species whose gonadal differentiation initiates at the yellow eel stage and is influenced by environmental factors. We revealed some sex-related genes were sex dimorphically expressed in gonads during gonadal sex differentiation of Japanese eel (Anguilla japonica); however, the expression of sex-related genes in the brain-pituitary during gonadal sex differentiation in eels is still unclear. This study aimed to investigate the sex-related gene expressions in the brain-pituitary and tried to clarify their roles in the brain and gonads during gonadal sex differentiation. Based on our previous histological study, the control eels developed as males, and estradiol-17β (E2) was used for feminization. Our results showed that during testicular differentiation, the brain cyp19a1 transcripts and aromatase proteins were increased significantly; moreover, the cyp19a1, sf-1, foxl2s, and esrs (except gperb) transcripts in the midbrain/pituitary also were increased significantly. Forebrain gnrh1 transcripts increased slightly during gonadal differentiation of both sexes, but the gnrhr1b and gnrhr2 transcripts in the midbrain/pituitary were stable during gonadal differentiation. The expression levels of gths and gh in the midbrain/pituitary were significantly increased during testicular differentiation and were much higher in males than in E2-feminized females. These results implied that endogenous estrogens might play essential roles in the brain/pituitary during testicular differentiation, sf-1, foxl2s, and esrs may have roles in cyp19a1 regulation in the midbrain/pituitary of Japanese eels. For the GnRH-GTH axis, gths, especially fshb, may be regulated by esrs and involved in regulating testicular differentiation and development in Japanese eels.

Triclosan, an antimicrobial drug, induced reproductive impairment in the freshwater fish, Anabas testudineus (Bloch, 1792)

Triclosan (TCS), an antimicrobial drug, is known to occupy different compartments in aquatic ecosystems. The present study focused to evaluate the reproductive toxicity of triclosan, at environmentally relevant (0.009 and 9 μg L-1) and sublethal (176.7 μg L-1) concentrations for 90 days in the pre-spawning phase of the fish, Anabas testudineus. The reproductive biomarkers, namely, gonadal steroidogenic enzymes, expression of aromatic genes, levels of serum gonadotropins, sex hormones, and histology of gonads were analyzed. The weight of the animal, brain weights along with gonadosomatic index decreased while mucus deposition increased significantly at all concentrations of triclosan as the primary defensive mechanism to prevent the entry of toxicants. Triclosan disrupted gonadal steroidogenesis as evidenced by a reduction in the activities of gonadal steroidogenic enzymes. The expressions of cyp19a1a and cyp19a1b genes were up-regulated in the brain of both sexes and testis, while down-regulated in the ovary indicating estrogenic effects of the compound. The endocrine-disrupting effects of triclosan were confirmed. The current results suggest that chronic exposure to triclosan altered reproductive endpoints thereby impairing normal reproductive functions in fish.

Integrative analysis of miRNA-mRNA expression in the brain during high temperature-induced masculinization of female Nile tilapia (Oreochromis niloticus)

Temperature is one of the most important non-genetic sex differentiation factors for fish. The technique of high temperature-induced sex reversal is commonly used in Nile tilapia (Oreochromis niloticus) culture, although the molecular regulatory mechanisms involved in this process remain unclear. The brain is an essential organ for the regulation of neural signals involved in germ cell differentiation and gonad development. To investigate the regulatory roles of miRNAs-mRNAs in the conversion of female to male Nile tilapia gender under high-temperature stress, we compared RNA-Seq data from brain tissues between a control group (28 °C) and a high temperature-treated group (36 °C). The result showed that a total of 123,432,984 miRNA valid reads, 288,202,524 mRNA clean reads, 1128 miRNAs, and 32,918 mRNAs were obtained. Among them, there were 222 significant differentially expressed miRNAs (DE miRNAs) and 810 differentially expressed mRNAs (DE mRNAs) between the two groups. Eight DE miRNAs and eight DE mRNAs were randomly selected, and their expression patterns were validated by qRT-PCR. The miRNA-mRNA co-expression network demonstrated that 40 DE miRNAs targeted 136 protein-coding genes. Functional enrichment analysis demonstrated that these genes were involved in several gonadal differentiation pathways, including the oocyte meiosis signaling pathway, progesterone-mediated oocyte maturation signaling pathway, cell cycle signaling pathway and GnRH signaling pathway. Then, an interaction network was constructed for 8 miRNAs (mir-137-5p, let-7d, mir-1388-5p, mir-124-4-5p, mir-1306, mir-99, mir-130b and mir-21) and 10 mRNAs (smc1al, itpr2, mapk1, ints8, cpeb1b, bub1, fbxo5, mmp14b, cdk1 and hrasb) involved in the oocyte meiosis signaling pathway. These findings provide novel information about the mechanisms underlying miRNA-mediated sex reversal in female Nile tilapia.

Evaluating the alterations of the estrogen-responsive genes in Cyprinodon variegatus larvae for biomonitoring the impacts of estrogenic endocrine disruptors (EEDs)

Currently, endocrine disruptors (EDs) can be found in all the environmental compartments. To understand the effects of estrogenic EDs (EEDs), adults of Cyprinodon variegatus have been classically used as a marine model. However, it is during development that exposure to contaminants may generate permanent consequences. Thus, the aim of this study was to verify the effects produced by acute exposure to 17α-ethinylestradiol (EE2) in C. variegatus larvae. Quantitative PCR (qPCR) results revealed the induction of vtg and zp gene expression on exposure to 1000 ng/L EE2 and the induction of vtgc, zp2, zp3 and cyp19a2, and inhibition of vtgab, wap and cyp1a1 on exposure to 100 ng/L EE2. Lower concentrations inhibited the gene expression of vtgab and wap (50 ng/L), cyp1a1 (25 ng/L) and zp2 (12.5 ng/L). These alterations in gene expression allow us to affirm that larvae of C. variegatus are an efficient and sensitive model for biomonitoring EEDs.

MPTP induces neurodegeneration by modulating dopaminergic activity in catfish brain

Tyrosine hydroxylase (Th) is an allosteric rate-limiting enzyme in catecholamine (CA) biosynthesis. The CAs, dopamine (DA), norepinephrine (NE), and epinephrine are important neurotransmitters wherein DA contributes a key role in the central nervous system of vertebrates. The present study evaluated DA and Th's significance in DA-ergic activity and neurodegeneration upon 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure in catfish. Further, the expression of certain brain-and ovary-related genes measured through qPCR were downregulated upon MPTP treatment which is in accordance with the decreased levels of L-Dopa, DA, and NE levels estimated through HPLC-ECD. Additionally, TEM analysis depicted structural disarray of brain upon MPTP exposure and also decreased serum levels of testosterone, 11-ketotestosterone, and estradiol-17β. MPTP treatment, in vitro, using primary brain cell culture resulted in diminished cell viability and increased ROS levels leading to elevated apoptotic cells significantly. Consequently, the study highlights the MPTP-induced neurodegeneration of the Th and DA-ergic activity in corroboration with female brain-related genes downregulation, also gonadal function as evidenced by depleted sex steroids level and low expression of ovary-related genes.

Molecular Cloning and Expression Responses of Jarid2b to High-Temperature Treatment in Nile Tilapia (Oreochromis niloticus)

Nile tilapia is a GSD + TE (Genetic Sex Determination + Temperature Effect) fish, and high-temperature treatment during critical thermosensitive periods (TSP) can induce the sex reversal of Nile tilapia genetic females, and brain transcriptomes have revealed the upregulation of Jarid2 (Jumonji and AT-rich domain containing 2) expression after 36 °C high-temperature treatment for 12 days during TSP. It was shown that JARID2 forms a complex with polycomb repressive complex 2 (PRC2) that catalyzed H3K27me3, which was strongly associated with transcriptional repression. In this study, Jarid2b was cloned and characterized in Nile tilapia, which was highly conserved among the analyzed fish species. The expression of Jarid2b was upregulated in the gonad of 21 dpf XX genetic females after 12-day high-temperature treatment and reached a similar level to that of males. Similar responses to high-temperature treatment also appeared in the brain, heart, liver, muscle, eye, and skin tissues. Interestingly, Jarid2b expression was only in response to high-temperature treatment, and not to 17α-methyltestosterone (MT) or letrozole treatments; although, these treatments can also induce the sex reversal of genetic Nile tilapia females. Further studies revealed that Jarid2b responded rapidly at the 8th hour after high-temperature treatment. Considering that JARID2 can recruit PRC2 and establish H3K27me3, we speculated that it might be an upstream gene participating in the regulation of Nile tilapia GSD + TE through regulating the H3K27 methylation level at the locus of many sex differentiation-related genes.

Molecular Cloning and Expression Analysis of Thyrotropin-Releasing Hormone, and Its Possible Role in Gonadal Differentiation in Rice Field eel Monopterus albus

Simple Summary

Thyrotropin-releasing hormone (TRH) is an important upstream regulator in the hypothalamus-pituitary-thyroid (HPT) axis in mammals. In this study, we isolated and characterized trh gene from a protogynous hermaphrodite fish rice field eel Monopterus albus. TRH had no significant effect on serum thyroid hormone levels in rice field eel. However, we found that TRH was involved in the regulation gonadal differentiation-related gene expression and serum sex steroid hormone secretion. Our results indicated that TRH may play a novel role in gonadal differentiation in rice field eel.

Abstract

Rice field eel (Monopterus albus), a protogynous hermaphrodite fish, is a good model for the research of sex determination and gonadal differentiation in teleosts. In this study, we cloned the full-length cDNA sequence of trh, which encoded a predicted protein with 270 amino acids. Trh mainly expressed in the brain, followed by the ovary, testis, muscle and pituitary, and had low levels in other peripheral tissues. During natural sex reversal, trh mRNA expression levels exhibited a significant increase at the late intersexual stage in the hypothalamus. In the gonad, trh mRNA expression levels showed a trend of increase followed by decrease, and only increased significantly at the middle intersexual stage. No matter static incubation or intraperitoneal (IP) injection, TRH had no significant effect on trh and thyroid-stimulating hormone βsubunit (tshβ) mRNA expression levels, and serum T3, T4 and TRH release. After static incubation of ovarian fragments by TRH, the expression of gonadal soma derived factor (gsdf) was up-regulated significantly at both the doses of 10 and 100 nM. IP injection of TRH stimulated the expression of gsdf, and inhibited the expression of ovarian aromatase gene (cyp19a1a), accompanied by the increase of serum 11-KT levels. The results indicated that TRH may play a novel role in gonadal differentiation by the regulation of gonadal differentiation-related gene expression and sex steroid hormone secretion in rice field eel.

Is serotonin uptake by peripheral tissues sensitive to hypoxia exposure?

In the Gulf toadfish (Opsanus beta), the serotonin (5-HT) transporter (SERT) is highly expressed in the heart, and the heart and gill both demonstrate the capacity for SERT-mediated uptake of 5-HT from the circulation. Because 5-HT is a potent vasoconstrictor in fish, we hypothesized that hypoxia exposure may increase 5-HT uptake by these tissues-and increase excretion of 5-HT-to prevent branchial vasoconstriction that would hamper gas exchange. Spot sampling of blood, bile, and urine revealed that fish exposed to chronic hypoxia (1.83 ± 0.12 mg·L^-1 O₂ for 24-26 h) had 41% lower plasma 5-HT in the ventral aorta (immediately following the heart) than in the hepatic vein (immediately before the heart), suggesting enhanced cardiac 5-HT uptake during hypoxia. 5-HT concentrations in the bile were greater than those in the urine, but there were no effects of acute (1.31 ± 0.06 mg·L^-1 O₂ for 25 min) or chronic hypoxia on 5-HT levels in these fluids. In 5-HT radiotracer experiments, the presence of tracer in the bile decreased upon hypoxia exposure, but, surprisingly, neither acute nor chronic hypoxia-induced changes in [³H]5-HT uptake in the heart, gill, or other tissues. Given the likely impact of the hypoxia exposure on metabolic rate, future studies should examine the effects of a milder hypoxia exposure on 5-HT uptake into these tissues and the role of 5-HT degradation.

Profile of gene expression changes during estrodiol-17β-induced feminization in the Takifugu rubripes brain

Background

As the critical tissue of the central nervous system, the brain has been found to be involved in gonad development. Previous studies have suggested that gonadal fate may be affected by the brain. Identifying brain-specific molecular changes that occur during estrodiol-17β (E₂) -induced feminization is crucial to our understanding of the molecular control of sex differentiation by the brains of fish.

Results

In this study, the differential transcriptomic responses of the Takifugu rubripes larvae brain were compared after E₂ treatment for 55 days. Our results showed that 514 genes were differentially expressed between E₂-treated-XX (E-XX) and Control-XX (C-XX) T. rubripes, while 362 genes were differentially expressed between E₂-treated-XY (E-XY) and Control-XY (C-XY). For example, the expression of cyp19a1b, gnrh1 and pgr was significantly up-regulated, while st, sl, tshβ, prl and pit-1, which belong to the growth hormone/prolactin family, were significantly down-regulated after E₂ treatment, in both sexes. The arntl1, bhlbe, nr1d2, per1b, per3, cry1, cipc and ciart genes, which are involved in the circadian rhythm, were also found to be altered. Differentially expressed genes (DEGs), which were identified between E-XX and C-XX, were significantly enriched in neuroactive ligand-receptor interaction, arachidonic acid metabolism, cytokine-cytokine receptor interaction and the calcium signaling pathway. The DEGs that were identified between E-XY and C-XY were significantly enriched in tyrosine metabolism, phenylalanine metabolism, arachidonic acid metabolism and linoleic acid metabolism.

Conclusion

A number of genes and pathways were identified in the brain of E₂-treated T. rubripes larvae by RNA-seq. It provided the opportunity for further study on the possible involvement of networks in the brain-pituitary-gonadal axis in sex differentiation in T. rubripes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08158-0.

Advances in Reproductive Endocrinology and Neuroendocrine Research Using Catfish Models

Catfishes, belonging to the order siluriformes, represent one of the largest groups of freshwater fishes with more than 4000 species and almost 12% of teleostean population. Due to their worldwide distribution and diversity, catfishes are interesting models for ecologists and evolutionary biologists. Incidentally, catfish emerged as an excellent animal model for aquaculture research because of economic importance, availability, disease resistance, adaptability to artificial spawning, handling, culture, high fecundity, hatchability, hypoxia tolerance and their ability to acclimate to laboratory conditions. Reproductive system in catfish is orchestrated by complex network of nervous, endocrine system and environmental factors during gonadal growth as well as recrudescence. Lot of new information on the molecular mechanism of gonadal development have been obtained over several decades which are evident from significant number of scientific publications pertaining to reproductive biology and neuroendocrine research in catfish. This review aims to synthesize key findings and compile highly relevant aspects on how catfish can offer insight into fundamental mechanisms of all the areas of reproduction and its neuroendocrine regulation, from gametogenesis to spawning including seasonal reproductive cycle. In addition, the state-of-knowledge surrounding gonadal development and neuroendocrine control of gonadal sex differentiation in catfish are comprehensively summarized in comparison with other fish models.

Epigenetic Regulation and Environmental Sex Determination in Cichlid Fishes

Studying environmental sex determination (ESD) in cichlids provides a phylogenetic and comparative approach to understand the evolution of the underlying mechanisms, their impact on the evolution of the overlying systems, and the neuroethology of life history strategies. Natural selection normally favors parents who invest equally in the development of male and female offspring, but evolution may favor deviations from this 50:50 ratio when environmental conditions produce an advantage for doing so. Many species of cichlids demonstrate ESD in response to water chemistry (temperature, pH, and oxygen concentration). The relative strengths of and the exact interactions between these factors vary between congeners, demonstrating genetic variation in sensitivity. The presence of sizable proportions of the less common sex towards the environmental extremes in most species strongly suggests the presence of some genetic sex-determining loci acting in parallel with the ESD factors. Sex determination and differentiation in these species does not seem to result in the organization of a final and irreversible sexual fate, so much as a life-long ongoing battle between competing male- and female-determining genetic and hormonal networks governed by epigenetic factors. We discuss what is and is not known about the epigenetic mechanism behind the differentiation of both gonads and sex differences in the brain. Beyond the well-studied tilapia species, the 2 best-studied dwarf cichlid systems showing ESD are the South American genus Apistogramma and the West African genus Pelvicachromis. Both species demonstrate male morphs with alternative reproductive tactics. We discuss the further neuroethology opportunities such systems provide to the study of epigenetics of alternative life history strategies and other behavioral variation.

Parental selection for growth and early-life low stocking density increase the female-to-male ratio in European sea bass

In European sea bass (Dicentrarchus labrax), as in many other fish species, temperature is known to influence the sex of individuals, with more males produced at relatively high temperatures. It is however unclear to what extent growth or stress are involved in such a process, since temperature is known to influence both growth rate and cortisol production. Here, we designed an experiment aiming at reducing stress and affecting early growth rate. We exposed larvae and juveniles originating from both captive and wild parents to three different treatments: low stocking density, food supplemented with tryptophan and a control. Low stocking density and tryptophan treatment respectively increased and decreased early growth rate. Each treatment influenced the stress response depending on the developmental stage, although no clear pattern regarding the whole-body cortisol concentration was found. During sex differentiation, fish in the low-density treatment exhibited lower expression of gr1, gr2, mr, and crf in the hypothalamus when compared to the control group. Fish fed tryptophan displayed lower crf in the hypothalamus and higher level of serotonin in the telencephalon compared to controls. Overall, fish kept at low density produced significantly more females than both control and fish fed tryptophan. Parents that have been selected for growth for three generations also produced significantly more females than parents of wild origin. Our findings did not allow to detect a clear effect of stress at the group level and rather point out a key role of early sexually dimorphic growth rate in sex determination.

Role of sox30 in regulating testicular steroidogenesis of common carp

Expression of transcription factors is crucial for the regulation of steroidogenesis and gonadal development in fish. SRY-related box (SOX) proteins regulate gene expression of various events related to vertebrate reproduction. This study reports the role of sox30 and its influence on sox9a/b in regulating testicular steroidogenesis of the common carp, Cyprinus carpio. Tissue distribution showed predominant expression of sox30 in gonads, while gonadal ontogeny indicated significant dimorphic expression of sox30 from 120 days post hatch. Higher sox30 transcripts during the spawning season, an elevation of sox30 after human chorionic gonadotropin induction, and 11-ketotestosterone (11-KT) treatment authenticate gonadotropin dependency. Treatment of 17α-methyl-di-hydroxy-testosterone to juvenile common carp for mono-sex induction, vis-à-vis elevated sox30 expression. Sox30 protein was detected abundantly in spermatocytes and spermatid/sperm of carp testis. Transient silencing of sox30 using small interfering RNAs decreased sox9a/b expression, lead to downregulation of certain molecule/factor, transcription factor, germ/stem cell marker, and steroidogenesis-related enzyme genes. Serum testosterone and 11-KT decreased significantly upon transient silencing of sox30, in vivo. Concomitantly, a reduction in testicular microsomal 11-β hydroxysteroid dehydrogenase activity was observed. These results demonstrate the influence of sox30 as well as sox9a/b in the regulation of testicular steroidogenesis in common carp.

Controlled release of sex steroids through osmotic pump alters brain GnRH1 and catecholaminergic system dimorphically in the catfish, Clarias gariepinus

The present study aimed to evaluate osmotic pump-mediated controlled release of estrogen in males and androgen in females to analyze the impact on gonadotropin-releasing hormone (GnRH1), catecholamines (CAs) and other associated genes in the catfish, Clarias gariepinus. During pre-spawning phase, catfish were separately implanted osmotic pumps loaded with 17β-estradiol (E₂) in males and 17α-methyltestosterone (MT) in females at a dose of 10 μg/100 μl or saline (100 μl) controls into both sexes to release for 21 days and all fishes were maintained as per the duration. Further, GnRH1 expression levels were analysed in the discrete regions of brain after E₂ and MT treatments in male and female catfish, respectively using qPCR which revealed that GnRH1 expression was significantly higher in E₂ treated male as compared to the control. On the other hand, GnRH1 expression was lower in MT treated female when compared to the control in the discrete regions of brain. In addition, certain brain and monoaminergic system related genes showed a differential response. Catfish GnRH1 could be localized in preoptic area-hypothalamus (POA-HYP) that correlated with the expression profile in the discrete regions of catfish brain. Serum levels of sex steroids in the treated male fish indicated that the treatment of E₂ could maintain and impart feminization effect even in the presence of endogenous androgen during gonadal recrudescence while such an effect was not seen in females with androgen treatment. Measurement of CAs, L-3,4-dihydroxyphenylalanine, dopamine and norepinephrine levels in the male and female brain after the controlled release of E₂ and MT, respectively confirmed the modulation of neurotransmitters in the E₂treated male than MT treated female fish. These results collectively suggest the severity of estrogenic over androgenic compounds to alter reproductive status even at a minimal dose by targeting CAs and GnRH1 at the level of brain of catfish. This study provides insights into the reproductive toxicity of sex steroid analogues at the level of brain GnRH1 and CA-ergic system in addition to serum T, 11-KT and E₂ levels during gonadal recrudescence, which is a crucial period of gametogenesis preceding spawning.

Analyses of mRNA-seq and miRNA-seq of the brain reveal the sex differences of gene expression and regulation before and during gonadal differentiation in 17β-estradiol or 17α-methyltestosterone-induced olive flounder (Paralichthys olivaceus)

Olive flounder (Paralichthys olivaceus) is a commercially important flatfish species cultured in East Asia. Female flounders generally grow more rapidly than males, therefore control of the sex ratio seems to be a proposed way to increase production. However, the sex determination gene and sex determination mechanism have yet been elucidated. The brain is an important organ that is involved in gonadal development. To explore the sex differences of gene expression in the brain before and during the flounder gonadal differentiation, we used messenger RNA (mRNA)-seq technology to investigate transcriptomes of male and female brains. Between female and male brains, 103 genes were differentially expressed before ovarian differentiation, 16 genes were differentially expressed before testicular differentiation, and 64 genes were differentially expressed during gonadal differentiation. According to annotation and Kyoto Encyclopedia of Genes and Genomes information, the differentially expressed genes (DEGs) were involved in circadian rhythm, circadian rhythm-fly, circadian entrainment, dopaminergic synapse, calcium signaling, glutamatergic synapse, taste transduction, herpes simplex infection, long-term depression, retrograde endocannabinoid signaling, and the synaptic vesicle cycle pathways. MicroRNA (miRNA)-seq was performed during the gonadal differentiation and the target genes of miRNAs were predicted. Integrated analysis of mRNA-seq and miRNA-seq showed that 29 of the 64 DEGs were regulated by the differentially expressed miRNAs during the gonadal differentiation. Our study provides a basis for further studies of brain sex differentiation and the molecular mechanism of sex determination in olive flounder.

Activation of the brain-pituitary-gonadotropic axis in the black porgy Acanthopagrus schlegelii during gonadal differentiation and testis development and effect of estradiol treatment

Previous studies revealed an estradiol (E2)-dependent peak in brain activity, including neurosteroidogenesis and neurogenesis in the black porgy during the gonadal differentiation period. The brain-pituitary-gonadotropic axis is a key regulator of reproduction and may also be involved in gonadal differentiation, but its activity and potential role in black porgy during the gonadal differentiation period is still unknown. The present study analyzed the expression of regulatory factors involved in the gonadotropic axis at the time of gonadal differentiation (90, 120, 150 days after hatching [dah]) and subsequent testicular development (180, 210, 300 dah). In agreement with previous studies, expression of brain aromatase cyp19a1b peaked at 120 dah, and this was followed by a gradual increase during testicular development. The expression of gonadotropin subunits increased slightly but not significantly during gonadal differentiation and then increased significantly at 300 dah. In contrast, the expression of brain gnrh1 and pituitary gnrh receptor 1 (gnrhr1) exhibited a pattern with two peaks, the first at 120 dah, during the period of gonadal differentiation, and the second peak during testicular development. Gonad fshr and lhcgr increased during gonadal differentiation period with highest transcript level in prespawning season during testicular development. This suggests that the early activation of brain gnrh1, pituitary gnrhr1 and gths, and gonad gthrs might be involved in the control of gonadal differentiation. E2 treatment increased brain cyp19a1b expression at each sampling time, in agreement with previous studies in black porgy and other teleosts. E2 also significantly stimulated the expression of pituitary gonadotropin subunits at all sampling times, indicating potential E2-mediated steroid feedback. In contrast, no significant effect of E2 was observed on gnrh1. Moreover, treatment of AI or E2 had no statistically significant effect on brain gnrh1 transcription levels during gonadal differentiation. This indicated that the early peak of gnrh1 expression during the gonadal differentiation period is E2-independent and therefore not directly related to the E2-dependent peak in brain neurosteroidogenesis and neurogenesis also occurring during this period in black porgy. Both E2-independent and E2-dependent mechanisms are thus involved in the peak expression of various genes in the brain of black porgy at the time of gonadal differentiation.

Profiling expression changes of genes associated with temperature and sex during high temperature-induced masculinization in the Nile tilapia brain

Fish sex-determining mechanisms can be classified as genotypic (GSD), temperature (TSD), or genotypic plus temperature effects (GSD+TE). Previous studies have shown that culturing water temperature during thermosensitive periods (TSP) could affect the expression of many genes in the gonad in some fish. However, few studies have focused on gene expression changes in the brain after temperature treatment during TSP in fish species. In this study, three families were developed by crossing XX neomales with XX females and one of them was used for transcriptome analysis. The results showed that a total of 105, 3164 and 4666 DEGs were respectively obtained in FC (female control) vs. FT (high temperature-treated females at TSP), FC vs. MC (male control), and MC vs. FT comparison groups. By profiling analysis, we show that the mRNA expression levels of 16 differentially expressed genes (DEGs) exhibited significant downregulation or upregulation after high temperature treatment and reached a similar level as that in MC. Among the 16 DEGs, LOC100699848 (lysine specific demethylase 6A) and Jarid2 contained JmjC domain, showing the possible important role of JmjC domain in response to temperature treatment in Nile tilapia. Kdm6b (lysine demethylase 6B) and Jarid2 have been shown to play important roles in reptile TSD, showing the relative conservation of underlying regulation mechanisms between TSD in reptile and TSD or GSD+TE in fish species. Finally, the transcriptome profiling was validated by quantitative real-time PCR in nine selected genes. These results provide a direction for investigating the GSD+TE molecular mechanism in fish species.

GDNF family receptor α-1 in the catfish: Possible implication to brain dopaminergic activity

Glial cell line-derived neurotrophic factor (GDNF)is a potent trophic factor that preferentially binds to GDNF family receptor α-1 (GFRα-1)by regulating dopaminergic (DA-ergic) neuronsin brain. Present study aimed to evaluate the significance of GFRα-1 expression during early brain development in catfish. Initially, the full-length cDNA of GFRα-1 was cloned from adult brain which showed high homology with other vertebrate counterparts. Quantitative PCR analysis of tissue distribution revealed ubiquitous expression of GFRα-1 in the tissues analyzed with high levels in female brain and ovary. Significant high expression was evident in brain at 75 and 100 days post hatch females than the respective age-match males. Expression of GFRα-1 was high in brain during the spawning phase when compared to other reproductive phases. Localization of GFRα-1 revealed its presence in preoptic area-hypothalamus which correlated well with the expression profile in discrete areas of brain in adult catfish. Transient silencing of GFRα-1through siRNA lowered expression levels of GFRα-1, which further down regulated the expression of certain brain-specific genes. Expression of GFRα-1 in brain declined significantly upon treatment with the 1-methyl-1,2,3,6-tetrahydropyridinecausing neurodegeneration which further correlated with catecholamines (CA), L-3,4-dihydroxyphenylalanine, DA and norepinephrine levels. Taken together, GFRα-1 plausibly entrains gonadotropin-releasing hormone and gonadotropin axiseither directly or indirectly, at least by partially targeting CA-ergic activity.

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.