Epigenetic regulation of gonadal and brain aromatase expression in a cichlid fish with environmental sex determination.

A fit animal must develop testes or ovaries, with brain and physiology to match. In species with alternative male morphs this coordination of development across tissues operates within sexes as well as between. For Pelvicachromis pulcher, an African cichlid in which early pH exposure influences both sex and alternative male morph, we sequence both copies of aromatase (cyp19a1), a key gene for sex determination. We analyze gene expression and epigenetic state, comparing gonad and brain tissue from females, alternative male morphs, and fry. Relative to brain, we find elevated expression of the A-copy in the ovaries but not testes. Methylation analysis suggests strong epigenetic regulation, with one region specifying sex and another specifying tissue. We find elevated brain expression of the B-copy with no sex or male morph differences. B-copy methylation follows that of the A-copy rather than corresponding to B-copy expression. In 30-day old fry, we see elevated B-copy expression in the head, but we do not see the expected elevated A-copy expression in the trunk that would reflect ovarian development. Interestingly, the A-copy epialleles that distinguish ovaries from testes are among the most explanatory patterns for variation among fry, suggesting epigenetic marking of sex prior to differentiation and thus laying the groundwork for mechanistic studies of epigenetic regulation of sex and morph differentiation.

Fullerene C60 nanomaterial induced oxidative imbalance in gonads of the freshwater fish, Anabas testudineus (Bloch, 1792).

The engineered carbon nanomaterial, fullerene C60, with unique physicochemical properties, released into the aquatic environment is known to formulate high risk factor for the aquatic life. The present study was aimed to investigate fullerene C60 induced oxidative imbalance in ovary and testis of the freshwater fish, Anabas testudineus. The median lethal concentration (96 h-LC50) of fullerene C60 in Anabas testudineus was 50 mg/ L, and fish exposed to two sublethal concentrations i.e., 5 mg/ L and 10 mg/ L (one-tenth and one-fifth of LC50) for short-term (24, 48, 72 and 96 h) and long-term (7, 15, 30 and 60 d) durations. The antioxidant parameters such as the activities of superoxide dismutase (SOD), catalase, glutathione reductase, glutathione peroxidase, the levels of hydrogen peroxide generation and lipid peroxidation were analyzed along with histopathological alterations in gonadal tissues. Both sublethal concentrations of fullerene C60 caused significant (P < 0.05) decrease in the activities of antioxidant enzymes, whereas the levels of hydrogen peroxide generation and lipid peroxidation increased significantly (P < 0.05) in gonads. Fullerene exposure significantly (P < 0.05) increased the mucous deposition with significant (P < 0.05) reduction in the weights of gonads and gonado-somatic index. The histopathological analysis showed prominent alterations in testis and ovary of treated fishes when compared to the control groups. After 60 d of sublethal exposure of fullerene C60, fish were left in the toxicant-free water for another 60 d, in which the changes in the activities of the gonadal antioxidant enzymes and histological alterations were not completely recovered. Hence, from the present study, it was illustrated that fullerene C60 caused oxidative imbalance in the gonads, which may possibly affect the reproductive potential of the fish, Anabas testudineus.

Effect of perfluorooctanesulfonate exposure on steroid hormone levels and steroidogenic enzyme activities in juvenile Silurana tropicalis.

The impact of the perfluoro-chemical, perfluorooctanesulfonate (PFOS), on gonadal steroidogenesis during sexual differentiation in Silurana tropicalis was examined because of its ubiquity in the environment, bioaccumulative nature and potential to disturb endocrine activity. A partial life cycle study exposing S. tropicalis to varying concentrations of PFOS 0.06, 0.13, 0.25, 0.50 and 1.0 mg PFOS/L [nominal]) was conducted. Gonad and plasma samples were collected from juvenile control specimens and organisms exposed to PFOS from early embryo through 150 days post-metamorphosis. Gonad CYP17, aromatase and 5α-reductase activities were measured. Plasma estradiol, testosterone, dihydrotestosterone (DHT) and gonadal testosterone were measured in both males and females. Increased plasma DHT and gonadal testosterone were found in PFOS-treated juvenile male S. tropicalis compared to controls. Decreased plasma estradiol, but not testosterone, was detected in PFOS-treated female S. tropicalis compared to controls. Plasma DHT was not detected and an increase in gonadal testosterone was detected in PFOS-treated female frogs. Female S. tropicalis exposed to PFOS exhibited a concentration-related decrease in the mean aromatase activity, but not 5α-reductase. PFOS exposure in male frogs induced a concentration-related increase in 5α-reductase activity, but did not alter aromatase activity compared to control frogs. A concentration-related increase in CYP 17,20-lyase activity, but not 17-hydroxylase activity, was found in both female and male S. tropicalis exposed to PFOS.

Transcriptomic Analysis of MAP3K1 and MAP3K4 in the Developing Marsupial Gonad.

MAPKs affect gonadal differentiation in mice and humans, but whether this applies to all mammals is as yet unknown. Thus, we investigated MAPK expression during gonadal differentiation and after treatment with oestrogen in a distantly related mammal, the marsupial tammar wallaby, using our model of oestrogen-induced gonadal sex reversal. High-throughput RNA-sequencing was carried out on gonads collected from developing tammar 2 days before birth to 8 days after birth to characterise MAPK and key sexual differentiation markers. Day 25 foetal testes were cultured for 120 h in control medium or medium supplemented with exogenous oestrogen and processed for RNA-seq to identify changes in gene expression in response to oestrogen. MAPK pathway genes in the tammar were highly conserved at the sequence and amino acid level with those of mice and humans. Marsupial MAP3K1 and MAP3K4 clustered together in a separate branch from eutherian mammals. There was a marked decrease in the expression of male-determining genes SOX9 and AMH and increase in the female marker FOXL2 in oestrogen-treated male gonads. Only MAP3K1 expression increased in male gonads in response to oestrogen while other MAPK genes remained unaffected. This study suggests that MAP3K1 can be influenced by exogenous oestrogens during gonadal differentiation in this marsupial.

Effects of triclosan (TCS) on hormonal balance and genes of hypothalamus-pituitary- gonad axis of juvenile male Yellow River carp (Cyprinus carpio).

Triclosan (TCS) is a broad spectrum antimicrobial agent which has been widely dispersed and determinated in the aquatic environment. However, the effects of TCS on reproductive endocrine in male fish are poorly understood. In this study, male Yellow River carp (Cyprinus carpio) were exposed to 0, 1/5, 1/10 and 1/20 LC50 (96 h LC50 of TCS to carp) TCS under semi-static conditions for 42 d. Vitellogenin (Vtg), 17ß-estradiol (E2), testosterone(T), gonadotropin (GtH), and gonadotropin-releasing hormone (GnRH) levels were measured by enzyme-linked immunosorbent assay (ELISA). Meanwhile, we also examined the mRNA expressions of aromatase, GtHs-ß, GnRH, estrogen receptor (Er), and androgen receptor (Ar) by quantitative Real-time Polymerase Chain Reaction (qRT-PCR). TCS induced Vtg levels of hepatopancreas, E2 levels of serum, and inhibited Ar and Er mRNA levels, suggesting that the induction of Vtg production by TCS was indirectly caused by non-Er pathways. TCS-induced Vtg levels by interfering with the reproductive axis at plenty of latent loci of male carps: (a) TCS exposure increased the aromatase mRNA expression of hypothalamus and gonad aromatase, consequently increasing serum concentrations of E2 to induce Vtg in hepatopancreas; (b) TCS treatment changed GtH-ß and GnRH mRNA expression and secretion, causing the disturbance of reproductive endocrine; (c) TCS exposure decreased Ar mRNA levels, indicating potential Ar-mediated antiandrogen action. These mechanisms showed that TCS may induce Vtg production in male carp by non-Er-mediated pathways.

Estrogen-regulated expression of cyp19a1a and cyp19a1b genes in swim-up fry of Labeo rohita.

P450 aromatase is the terminal enzyme in the steroidogenic pathway and catalyzes the conversion of androgens to estrogens. The expression of cyp19a1 genes in brain and gonad of Indian major carp, Labeo rohita swim-up fry was measured by quantitative real-time polymerase chain-reaction. Results demonstrated that cyp19a1b and cyp19a1a predominate in brain and gonad respectively. Treatment of fry with an aromatase inhibitor fadrozole for 6days attenuated brain cyp19a1b expression, but not cyp19a1a of gonad. Fadrozole also attenuated brain aromatase activity. Treatment with 17ß-estradiol (E2) for 6days resulted in up-regulation of brain cyp19a1b transcripts in a dose- and time-dependent manner, but not cyp19a1a. Whole-body concentration of vitellogenin also increased in response to E2. Altogether, these results indicate L. rohita swim-up fry can be used to detect environmental estrogens either using vitellogenin induction or cyp19a1b gene expression.

Single-Cell RNA-Seq Analysis Maps Development of Human Germline Cells and Gonadal Niche Interactions.

Human fetal germ cells (FGCs) are precursors to sperm and eggs and are crucial for maintenance of the species. However, the developmental trajectories and heterogeneity of human FGCs remain largely unknown. Here we performed single-cell RNA-seq analysis of over 2,000 FGCs and their gonadal niche cells in female and male human embryos spanning several developmental stages. We found that female FGCs undergo four distinct sequential phases characterized by mitosis, retinoic acid signaling, meiotic prophase, and oogenesis. Male FGCs develop through stages of migration, mitosis, and cell-cycle arrest. Individual embryos of both sexes simultaneously contain several subpopulations, highlighting the asynchronous and heterogeneous nature of FGC development. Moreover, we observed reciprocal signaling interactions between FGCs and their gonadal niche cells, including activation of the bone morphogenic protein (BMP) and Notch signaling pathways. Our work provides key insights into the crucial features of human FGCs during their highly ordered mitotic, meiotic, and gametogenetic processes in vivo.

Identification and characterization of a catechol-o-methyltransferase cDNA in the catfish Heteropneustes fossilis: Tissue, sex and seasonal variations, and effects of gonadotropin and 2-hydroxyestradiol-17ß on mRNA expression.

Catechol-O-methyltransferase (COMT) is involved in the methylation and inactivation of endogenous and xenobiotic catechol compounds, and serves as a common biochemical link in the catecholamine and catecholestrogen metabolism. Studies on cloning, sequencing and function characterization comt gene in lower vertebrates like fish are fewer. In the present study, a full-length comt cDNA of 1442bp with an open-reading frame (ORF) of 792bp, and start codon (ATG) at nucleotide 162 and stop codon (TAG) at nucleotide 953 was isolated and characterized in the stinging catfish Heteropneustes fossilis (accession No. KT597925). The ORF codes for a protein of 263 amino acid residues, which is also validated by the catfish transcriptome data analysis. The catfish Comt shared conserved putative structural regions important for S-adenosyl methionine (AdoMet)- and catechol-binding, transmembrane regions, two glycosylation sites (N-65 and N-91) at the N-terminus and two phosphorylation sites (Ser-235 and Thr-240) at the C-terminus. The gene was expressed in all tissues examined and the expression showed significant sex dimorphic distribution with high levels in females. The transcript was abundant in the liver, brain and gonads and low in muscles. The transcripts showed significant seasonal variations in the brain and ovary, increased progressively to the peak levels in spawning phase and then declined. The brain and ovarian comt mRNA levels showed periovulatory changes after in vivo and in vitro human chorionic gonadotropin (hCG) treatments with high fold increases at 16 and 24h in the brain and at 16h in the ovary. The catecholestrogen 2-hydroxyE2 up regulated ovarian comt expression in vitro with the highest fold increase at 16h. The mRNA and protein was localized in the follicular layer of the vitellogenic follicles and in the cytoplasm of primary follicles. The data were discussed in relation to catecholamine and catecholestrogen-mediated functions in the brain and ovary of the stinging catfish.

Effects of Tin on Enzyme Activity in Holothuria grisea (Echinodermata: Holothuroidea).

This study evaluated the effect of tin exposure on enzyme activity in the sea cucumber (Holothuria grisea Selenka, 1867). After exposure to 0 (control), 0.04, 0.08, or 0.12 mg L-1 tin, we tested the activities of total cholinesterase in longitudinal muscles, acid phosphatase in gonads and the respiratory tree, as well as alkaline phosphatase in the intestines during a 96-h bioassay. Regression analyses showed that all enzyme activities declined with increasing tin concentrations, except for acid phosphatase in the respiratory tree, which were similarly, inhibited at all tin concentrations. These results indicate that H. grisea is a potential bioindicator for seascape habitat monitoring programs, as its biochemical markers show sensitivity to trace elements that can indicate a rise in pollution levels.

Histochemical and immunohistochemical studies of the gonads and paramesonephric ducts of male and female hatchlings of loggerhead sea turtles (Caretta caretta).

The sex of neonatal sea turtles is difficult to determine, because neonates lack heteromorphic sex chromosomes and dimorphic external characteristics; internal dimorphic morphology is defined at hatching. We used histochemical staining and made measurements in the gonads and paramesonephric ducts (PD) of both sexes to determine structural differences in female and male loggerhead sea turtle (Caretta caretta) hatchlings. We detected differences in the gonads and PD between the sexes including the amounts of mucopolysaccharides, collagen and elastic fibers. We determined that the thickness of the gonadal cortex and the diameter of the PD lumen are reliable sex-specific characteristics. We also assessed immunolocalization of aromatase, an enzyme complex that converts androgens to estrogens, and found differences in the localization and intensity of aromatase immunostaining in the gonads and PD of female and male hatchlings. Comprehensive studies of the sexual differences of sea turtles are important for conservation programs.

A novel ubiquitin-protein ligase E3 functions as a modulator of immune response against lipopolysaccharide in Pacific oyster, Crassostrea gigas.

Ubiquitination is an important post-translational protein modification and plays a crucial role in various processes such as cell cycle, signal transduction, and transcriptional regulation. In the present study, a novel ubiquitin (Ub)-protein ligase E3 (designed as CgE3Rv1) was identified from Crassostrea gigas, and its ubiquitination regulation in the immune response against lipopolysaccharide (LPS) stimulation was investigated. The open reading frame of CgE3Rv1 gene was of 1455 bp encoding a polypeptide of 484 amino acids with the predicted molecular mass of 54.89 kDa. There were two transmembrane regions and a RING-variant (RINGv) domain identified in CgE3Rv1. CgE3Rv1 shared similar C4HC3 zinc-finger-like motif with those RINGv domain Ub-protein ligases E3s identified from vertebrates and invertebrates, and it was closely clustered with the membrane-associated RING-CH2 (MARCH2) Ub-protein ligases E3s in the phylogenetic tree. The mRNA transcript of CgE3Rv1 was highest expressed in gonads and hemolymph (p < 0.05), and its mRNA expression level in hemocytes was significantly increased at 6 h (p < 0.01) after the stimulation of LPS, while the up-regulated mRNA expression was significantly decreased (p < 0.01) after acetylcholine stimulation. No significant changes of CgE3Rv1 expression were observed after peptidoglycan or mannan stimulation. Immunohistochemistry and in situ hybridization assays revealed that CgE3Rv1 protein and mRNA were dominantly distributed in the gonad. In the hemocytes, CgE3Rv1 was mainly located around the nucleus, and slightly distributed in the cytoplasm and on the cell membrane. Recombinant CgE3Rv1 RINGv domain protein (rCgE3Rv1-RINGv) was confirmed to activate the Ub reaction system in vitro with the aid of Ub-activating enzyme E1 and Ub-conjugating enzyme E2. These results demonstrated that CgE3Rv1 was an Ub-protein ligase E3, which was involved in the immune response against LPS and the interaction with cell surface signal molecules of neuroendocrine-immune system in oysters.

The chronic effects of lignin-derived bisphenol and bisphenol A in Japanese medaka Oryzias latipes.

One of the ultimate goals of green chemistry is to produce greener and more environmentally friendly chemicals to replace the existing toxic chemicals. In this study, Japanese medaka were exposed to 1.5mg/L of bisphenol A or lignin-derived bisphenol for 60 days, and the expressions of various biochemical markers, effects on reproduction, and histopathology were evaluated. The results showed that concentrations of liver vitellogenin of LD-BP exposed males were approximately 125% higher compared to the control males. Total number of eggs from the BPA and LD-BP exposed fish was approximately 47% (p<0.001) and 25% (p<0.05) less than the control fish, respectively. Total number of brood was lower from the BPA (46%, p<0.05) and LD-BP (17%, p<0.05) exposed fish than that of the control fish. Relative to the control fish, catalase and glutathione-S-transferase were significantly affected by the two chemicals in all tested tissues. BPA and LD-BP caused lipid peroxidation in all the tested tissues. Furthermore, acetylcholinesterase and α-glucosidase activity were significantly inhibited. Histopathological analysis showed that both the testis and ovary were mildly damaged by both chemicals. LD-BP affected medaka slightly more severe than BPA except on the reproduction, which was most likely due to different uptake, translocation, binding to targets and metabolism. Our results demonstrated that chronic exposure to both chemicals caused several adverse effects to medaka. Further research on the toxicity of LD-BP to other aquatic organisms is needed before substitution of traditional BPA with LD-BP can be recommended.

Sex chromosome complement determines sex differences in aromatase expression and regulation in the stria terminalis and anterior amygdala of the developing mouse brain.

Aromatase, which converts testosterone in estradiol, is involved in the generation of brain sex dimorphisms. Here we used the "four core genotypes" mouse model, in which the effect of gonadal sex and sex chromosome complement is dissociated, to determine if sex chromosomes influence the expression of brain aromatase. The brain of 16 days old XY mouse embryos showed higher aromatase expression in the stria terminalis and the anterior amygdaloid area than the brain of XX embryos, independent of gonadal sex. Furthermore, estradiol or dihydrotestosterone increased aromatase expression in cultures of anterior amygdala neurons derived from XX embryos, but not in those derived from XY embryos. This effect was also independent of gonadal sex. The expression of other steroidogenic molecules, estrogen receptor-α and androgen receptor was not influenced by sex chromosomes. In conclusion, sex chromosomes determine sex dimorphisms in aromatase expression and regulation in the developing mouse brain.

Caenorhabditis elegans EXO-3 contributes to longevity and reproduction: differential roles in somatic cells and germ cells.

Apurinic/apyrimidinic (AP) sites are the major DNA damage generated continuously even under normal conditions, and inhibit DNA replication/transcription. AP endonucleases are ubiquitous enzymes required for the repair of AP sites and 3' blocking ends, but their physiological roles in multicellular organisms are not fully understood. In this study, we investigated how an AP endonuclease functions in a multicellular organism (Caenorhabditis elegans (C. elegans)). EXO-3 is one of the AP endonucleases in C. elegans. Using an exo-3 mutant worm, we found that deletion of the exo-3 gene caused shortened lifespan in an ung-1-dependent manner. UNG-1 is a uracil DNA glycosylase in C. elegans, and the present finding suggested that UNG-1 is the major producer of AP sites that affects lifespan, and EXO-3 contributes to longevity by completing the repair of uracil. Next we found that the exo-3 gene was abundantly expressed in the gonads, and AP sites in the gonad were efficiently repaired, suggesting that EXO-3 functioned particularly in the gonad. Deletion of the exo-3 gene resulted in a significant decrease in self-brood size. This was rescued by deficiency of NTH-1, which is a bifunctional DNA glycosylase in C. elegans that recognizes oxidative base damage. This result suggested that the major substrate of EXO-3 in the gonad was 3' blocking end generated by NTH-1, and that EXO-3 played an important role in reproduction. A contribution of EXO-3 to reproduction was also suggested by our finding here that the decrease of self-brood size of the exo-3 mutant became more marked when worms were treated with methyl methanesulfonate (MMS) and sodium bisulfite (NaHSO3). This study demonstrated differential roles of EXO-3 in somatic cells and germ cells.

Development and steroidogenic properties of the Bidder's organ of the tadpole of Rhinella arenarum (Amphibia, Anura).

Several studies suggested that in anuran amphibians steroidogenic enzymes are critical for gonadal differentiation, proposing that the amount of sex steroids would adjust this differentiation. Among anurans, bufonids are important for the study of sex differentiation due to the presence of Bidder's organ (BO) that differentiates as a rudimentary ovary in the cephalic portion of the genital ridge. Considering that in adult males of Rhinella arenarum, the BO synthesizes estradiol, the main purpose of this work is to examine, in this species, the morphogenesis of BO and the steroidogenic capacity of this organ during larval development. BO and the proper gonads are distinguished from Gosner stage 26. During metamorphosis, BO primary oogonia develop in oogonia in nests, early previtellogenic oocytes and late previtellogenic oocytes in follicles while proper gonads remain undifferentiated. Aromatase was detected by immunohistochemistry in almost all the largest follicles of the BOs while the cytochrome P450 side-chain cleavage was observed in only few oocytes. The proper gonad was not immunoreactive in any stage. The determination of aromatase and 5α-reductase activities showed that the population of tadpoles between stages 36-41 is not homogeneous in terms of aromatase activity. In addition, from stage 26 to the end of metamorphosis, all the stages were able to produce estradiol from endogenous substrate but stages 40-41, corresponding to the end of pro-metamorphosis, produced the highest values. In conclusion, BO is able to synthesize estradiol from endogenous precursors and proper gonad remains undifferentiated at least until the end of the metamorphosis.

The in vitro interference of synthetic progestogens with carp steroidogenic enzymes.

Synthetic progestogens represent a class of pharmaceuticals widely used in oral contraceptives and in hormone replacement therapies. They reach the aquatic environment through wastewater effluents; however, environmental concentrations and effects on non-target organisms are poorly known. Given the important role of progestogens regulating fish spawning processes, this study aimed at assessing the in vitro interference of four currently used progestogens-drospirenone (DRO), levonorgestrel (LNG), norethindrone (NOR) and cyproterone acetate (CPA) - with key enzymatic activities involved in the synthesis of active steroids in carp (Cyprinus carpio). The enzymatic pathways investigated were (a) CYP17 (C17,20-lyase) and CYP11ß involved in the synthesis of androgens, (b) CYP19 that catalyses the aromatization of androgens to estrogens, and (c) 20ß-hydroxysteroid dehydrogenase (20ß-HSD) responsible for the synthesis of maturation-inducing hormones. All tested progestogens significantly inhibited the synthesis of androgens: DRO (IC50: 3.8 µM) was the strongest inhibitor of CYP17 followed by CPA (IC50s: 183 µM). Moreover, NOR (IC50: 0.4 µM), DRO (IC50: 1.8 µM) and CPA (IC50s: 87 µM) inhibited CYP11ß. An inhibition by NOR of ovarian CYP19 activity, and by DRO and CPA of 20ß-HSD was also observed, but at rather high concentrations (500 µM). Overall, this study highlights the potential of synthetic progestogens, and particularly DRO and NOR, to interfere with the biosynthesis of androgens in carp gonads.

Sex-dependent activity of de novo methyltransferase 3 (Tudnmt3) in the two-spotted mite, Tetranychus urticae†Koch.

DNA methylation is an epigenetic mechanism for regulating developmental and other important processes in eukaryotes. Several components of the DNA methylation machinery have been identified, such as DNA methyltransferases. However, little is known about DNA methyltransferases in chelicerates, which is the second largest arthropod group. Epigenetics are expected to have a crucial role in the metabolism and development of this group. Here, we investigated the role of DNA methyltransferase 3 in the development of Tetranychus urticae Koch. In silico analyses clearly showed that this enzyme possesses the necessary conserved motifs for the catalytic activity of de novo methylation of DNA. Real-time PCR revealed that T. urticae de novo methyltransferase 3 (Tudnmt3) is expressed ubiquitously and throughout the life cycle of the two-spotted spider mite. However, the pattern of Tudnmt3 expression was sex-dependent during the adult stage. Whole in situ hybridization provided supportive evidence that Tudnmt3 is linked to the differentiation of the gonads in adult females and males. Methylation-sensitive amplification polymorphism analyses of 119 loci showed that the status of DNA methylation is partially different between adult females and males, raising the possibility that this sex-dependent DNA methylation pattern is mediated by different methylation activity of Tudnmt3.

DNA methylation in the 5' flanking region of cytochrome P450 17 in adult rare minnow Gobiocypris rarus - tissue difference and effects of 17α-ethinylestradiol and 17α-methyltestoterone exposures.

Cytochrome P450 17 (CYP17) plays a vital role in hormone production in the body. In our previous study, mRNA expression of cyp17a1 was regulated by endocrine disrupting chemicals in rare minnow Gobiocypris rarus. However, the mechanism underlying the regulation is unclear. In the present study, we aim to explore whether the differential expression of cyp17a1 in distinct tissues and the modulation of its expression upon 17α-ethinylestradiol (EE2) and 17α-methyltestoterone (MT) are related to the DNA methylation status in G. rarus. The 732-bp fragment of 5' flanking region of cyp17a1 gene was isolated in G. rarus. The bisulfite sequencing PCR result showed that DNA methylation levels in 5' flanking of cyp17a1 in the gonads were significantly lower than those in the brains, which is negatively related to its mRNA expression in the 2 tissues in the previous study. The 7-day EE2 exposure of 25 ng/L caused a significant increase of methylation levels of cyp17a1 gene and a significant decrease of its transcript in testis. While 100 ng/L MT exposure for 7 days caused a significant decrease of methylation levels of cyp17a1 gene and a significant increase of its transcript in the ovary. The present findings indicate that the methylation status of cyp17a1 gene is negatively correlated with its mRNA expression in response to EE2 and MT in G. rarus. We hypothesize that the regulation of cyp17a1 expression by EE2 and MT might attribute to the change of its DNA methylation status in G. rarus.

Sexually dimorphic expression of vasa isoforms in the tongue sole (Cynoglossus semilaevis).

The vasa gene encodes an ATP-dependent RNA helicase of the DEAD box protein family that functions in a broad range of molecular events involving duplex RNA. In most species, the germline specific expression of vasa becomes a molecular marker widely used in the visualization and labeling of primordial germ cells (PGCs) and a tool in surrogate broodstock production through PGC transplantation. The vasa gene from tongue sole (Cynoglossus semilaevis) was characterized to promote the development of genetic breeding techniques in this species. Three C. semilaevis vasa transcripts were isolated, namely vas-l, vas-m, and vas-s. Quantitative real-time PCR results showed that C. semilaevis vasa transcripts were prevalently expressed in gonads, with very weak expression of vas-s in other tissues. Embryonic development expression profiles revealed the onset of zygotic transcription of vasa mRNAs and the maternal deposit of the three transcripts. The genetic ZW female juvenile fish was discriminated from genetic ZZ males by a pair of female specific primers. Only the expression of vas-s can be observed in both sexes during early gonadal differentiation. Before PGCs started mitosis, there was sexually dimorphic expression of vas-s with the ovary showing higher levels and downward trend. The results demonstrated the benefits of vasa as a germline specific marker for PGCs during embryonic development and gonadal differentiation. This study lays the groundwork for further application of C. semilaevis PGCs in fish breeding.

Localization of apoptotic and proliferating cells and mRNA expression of caspases and Bcl-2 in gonads of chicken embryos.

The aim of the present study was to analyze participation of apoptosis and proliferation in gonadal development in the chicken embryo by: (1) localization of apoptotic (TUNEL) and proliferating (PCNA immunoassay) cells in male and female gonads and (2) examination of mRNA expression (RT-PCR) of caspase-3, caspase-6 and Bcl-2 in the ovary and testis during the second half of embryogenesis and in newly hatched chickens. Apoptotic cells were found in gonads of both sexes. At E18 the percentage of apoptotic cells (the apoptotic index, AI) in the ovarian medulla and the testis was lower (p<0.05) than in the ovarian cortex. In the ovarian medulla, the AI at E18 was lower (p<0.05) than on E12. In the testis, the AI was significantly lower (p<0.05) at E18 than at E15 and 1D. The percentage of proliferating cells (the proliferation index: PI) within the ovary significantly increased from E15 to 1D in the cortex, while proliferating cells in the medulla were detected only at E15. In the testis, the PI gradually increased from E12 to 1D. The mRNA expression of caspase-3 and -6 as well as Bcl-2 was detected in male and female gonads at days 12 (E12), 15 (E15) and 18 (E18) of embryogenesis and the day after hatching (1D). The expression of all analyzed genes on E12 was significantly higher (p<0.05) in female than in male gonads. This difference was also observed at E15 and E18, but only for the caspase-6. The results obtained showed tissue- and sex-dependent differences in the number of apoptotic and proliferating cells as well as mRNA expression of caspase-3, -6 and Bcl-2 genes in the gonads of chicken embryos. Significant increase in the number of proliferating cells in the ovarian cortex and lack of these cells in the ovarian medulla (stages E12, E18, 1D) simultaneous with decrease in the intensity of apoptosis only in the medulla indicates that proliferation is the dominant process involved in the cortical development, which constitutes the majority of the functional structure of the fully developed ovary. No pronounced changes in the expression of apoptosis-related genes found during embryogenesis suggest that they cannot be considered as important indicators of gonad development. The molecular mechanisms of the regulation of balance between apoptosis and proliferation in developing avian gonads need to be further investigated.