Sequence and expression of cytochrome P450 aromatase and FTZ-F1 genes in the protandrous black porgy (Acanthopagrus schlegeli)

Molecular identification of genes involved in testicular steroid synthesis and characterization of the responses to hormones stimulation in testis of Japanese sea bass (Lateolabrax japonicas)

Testicular steroids are critical hormones for the regulation of spermatogenesis in male teleosts and their productions have been reported to be regulated by gonadotropins and gonadotropin-releasing hormone. In the Japanese sea bass (Lateolabrax japonicas), the reproductive endocrine, particularly regarding the production and regulation of testicular steroids, are not well understood. For this reason, we first cloned and characterized the response of several key genes regulating the production of testicular steroids and, second, we analyzed the changes of mRNA profiles of these genes during testicular development cycle and in the administration of hCG and GnRHa with corresponding testosterone level in serum, GSI and histological analyses. We succeeded in cloning the full-length cDNAs for the fushi tarazu factor-1 (FTZ-F1) homologues (FTZ-F1a and FTZ-F1b), steroidogenic acute regulatory protein (StAR) and anti-Müllerian hormone (AMH) in Japanese sea bass. Multiple sequence alignment and phylogenetic analysis of these proteins clearly showed that these genes in Japanese sea bass were homologous to those of other piscine species. During the testicular development cycle and hCG/GnRHa administration, quantification of jsbStAR transcripts revealed a trend similar to their serum testosterone levels, while a reciprocal relationship was founded between the serum concentrations of testosterone and jsbAMH and the links between gonadal expression of jsbStAR, jsbAMH and jsbFTZ-F1 were also observed. Our results have identified for the first time several key genes involved in the regulation of steroid production and spermatogenesis in the Japanese sea bass testis and these genes are all detected under gonadotropic hormone and gonadotropin-releasing hormone control.

Epigenetic modifications during sex change repress gonadotropin stimulation of cyp19a1a in a teleost ricefield eel (Monopterus albus)

In vertebrates, cytochrome P450 aromatase, encoded by cyp19a1, converts androgens to estrogens and plays important roles in gonadal differentiation and development. The present study examines whether epigenetic mechanisms are involved in cyp19a1a expression and subsequent gonadal development in the hermaphroditic ricefield eel. The expression of the ricefield eel cyp19a1a was stimulated by gonadotropin via the cAMP pathway in the ovary but not the ovotestis or testis. The CpG within the cAMP response element (CRE) of the cyp19a1a promoter was hypermethylated in the ovotestis and testis compared with the ovary. The methylation levels of CpG sites around CRE in the distal region (region II) and around steroidogenic factor 1/adrenal 4 binding protein sites and TATA box in the proximal region (region I) were inversely correlated with cyp19a1a expression during the natural sex change from female to male. In vitro DNA methylation decreased the basal and forskolin-induced activities of cyp19a1a promoter. Chromatin immunoprecipitation assays indicated that histone 3 (Lys9) in both regions I and II of the cyp19a1a promoter were deacetylated and trimethylated in the testis, and in contrast to the ovary, phosphorylated CRE-binding protein failed to bind to these regions. Lastly, the DNA methylation inhibitor 5-aza-2'-deoxycytidine reversed the natural sex change of ricefield eels. These results suggested that epigenetic mechanisms involving DNA methylation and histone deacetylation and methylation may abrogate the stimulation of cyp19a1a by gonadotropins in a male-specific fashion. This may be a mechanism widely used to drive natural sex change in teleosts as well as gonadal differentiation in other vertebrates.

Molecular cloning and expression analysis of fushi tarazu factor 1 in the brain of air-breathing catfish, Clarias gariepinus

Background

Fushi tarazu factor 1 (FTZ-F1) encodes an orphan nuclear receptor belonging to the nuclear receptor family 5A (NR5A) which includes adrenal 4-binding protein or steroidogenic factor-1 (Ad4BP/SF-1) and liver receptor homologue 1 (LRH-1) and plays a pivotal role in the regulation of aromatases.

Methodology/Principal Findings

Present study was aimed to understand the importance of FTZ-F1 in relation to brain aromatase (cyp19a1b) during development, recrudescence and after human chorionic gonadotropin (hCG) induction. Initially, we cloned FTZ-F1 from the brain of air-breathing catfish, Clarias gariepinus through degenerate primer RT-PCR and RACE. Its sequence analysis revealed high homology with other NR5A1 group members Ad4BP/SF-1 and LRH-1, and also analogous to the spatial expression pattern of the latter. In order to draw functional correlation of cyp19a1b and FTZ-F1, we analyzed the expression pattern of the latter in brain during gonadal ontogeny, which revealed early expression during gonadal differentiation. The tissue distribution both at transcript and protein levels revealed its prominent expression in brain along with liver, kidney and testis. The expression pattern of brain FTZ-F1 during reproductive cycle and after hCG induction, in vivo was analogous to that of cyp19a1b shown in our earlier study indicating its involvement in recrudescence.

Conclusions/Significance

Based on our previous results on cyp19a1b and the present data, it is plausible to implicate potential roles for brain FTZ-F1 in ovarian differentiation and recrudescence process probably through regulation of cyp19a1b in teleosts. Nevertheless, these interactions would require primary coordinated response from ovarian aromatase and its related transcription factors.

Aromatase (P450arom) and 11beta-hydroxylase (P45011beta) genes are differentially expressed during the sex change process of the protogynous rice field eel, Monopterus albus

Steroids are known to play a crucial role in gonadal sex differentiation in many non-mammalian vertebrates, but also in the gonadal sex change of hermaphroditic teleosts. We investigated the expression of two genes encoding key steroidogenic enzymes, i.e., cytochrome P450 aromatase (P450arom) and cytochrome P45011beta-hydroxylase (P45011beta), during the sex change of the protogynous rice field eel, Monopterus albus. Using RT-PCR with degenerate primers, we cloned rice field eel homologous fragments for both genes (rcP450arom and rcP45011beta) as indicated by the high level of homology with P450arom and P45011beta sequences from various vertebrates. Gonadal expression of rcP450arom and rcP45011beta mRNA levels were then assessed during the sex change by semi-quantitative RT-PCR and a real-time RT-PCR. rcP450arom was predominantly expressed in ovary, much less in ovotestis, and barely in testis. Conversely, P45011beta was markedly up-regulated at the onset of testicular development. These findings underline that regulation of steroidogenesis is an important process in the sex change of protogynous rice field eel, and they clearly indicate that the concomitant down-regulation of P450arom and up-regulation of P45011beta are of pivotal importance to the sex change of this species.

Interference of endocrine disrupting chemicals with aromatase CYP19 expression or activity, and consequences for reproduction of teleost fish

Many natural and synthetic compounds present in the environment exert a number of adverse effects on the exposed organisms, leading to endocrine disruption, for which they were termed endocrine disrupting chemicals (EDCs). A decrease in reproduction success is one of the most well-documented signs of endocrine disruption in fish. Estrogens are steroid hormones involved in the control of important reproduction-related processes, including sexual differentiation, maturation and a variety of others. Careful spatial and temporal balance of estrogens in the body is crucial for proper functioning. At the final step of estrogen biosynthesis, cytochrome P450 aromatase, encoded by the cyp19 gene, converts androgens into estrogens. Modulation of aromatase CYP19 expression and function can dramatically alter the rate of estrogen production, disturbing the local and systemic levels of estrogens. In the present review, the current progress in CYP19 characterization in teleost fish is summarized and the potential of several classes of EDCs to interfere with CYP19 expression and activity is discussed. Two cyp19 genes are present in most teleosts, cyp19a and cyp19b, primarily expressed in the ovary and brain, respectively. Both aromatase CYP19 isoforms are involved in the sexual differentiation and regulation of the reproductive cycle and male reproductive behavior in diverse teleost species. Alteration of aromatase CYP19 expression and/or activity, be it upregulation or downregulation, may lead to diverse disturbances of the above mentioned processes. Prediction of multiple transcriptional regulatory elements in the promoters of teleost cyp19 genes suggests the possibility for several EDC classes to affect cyp19 expression on the transcriptional level. These sites include cAMP responsive elements, a steroidogenic factor 1/adrenal 4 binding protein site, an estrogen-responsive element (ERE), half-EREs, dioxin-responsive elements, and elements related to diverse other nuclear receptors (peroxisome proliferator activated receptor, retinoid X receptor, retinoic acid receptor). Certain compounds including phytoestrogens, xenoestrogens, fungicides and organotins may modulate aromatase CYP19 activity on the post-transcriptional level. As is shown in this review, diverse EDCs may affect the expression and/or activity of aromatase cyp19 genes through a variety of mechanisms, many of which need further characterization in order to improve the prediction of risks posed by a contaminated environment to teleost fish population.

Characterization and expression profile of the ovarian cytochrome P-450 aromatase (cyp19A1) gene during thermolabile sex determination in pejerrey,Odontesthes bonariensis

Cytochrome P450 aromatase (cyp19) is an enzyme that catalyzes the conversion of androgens to estrogens and may play a role in temperature-dependent sex determination (TSD) of reptiles, amphibians, and fishes. In this study, the ovarian P450 aromatase form (cyp19A1) of pejerrey Odontesthes bonariensis, a teleost with marked TSD, was cloned and its expression profile evaluated during gonadal differentiation at feminizing (17 degrees C, 100% females), mixed-sex producing (24 and 25 degrees C, 73.3 and 26.7% females, respectively), and masculinizing (29 degrees C, 0% females) temperatures. The deduced cyp19A1 amino acid sequence shared high identity (>77.8%) with that from other teleosts but had low identity (<61.8%) with brain forms (cyp19A2), including that of pejerrey itself. The tissue distribution analysis of cyp19A1 mRNA in adult fish revealed high expression in the ovary. Semi-quantitative reverse transcription polymerase chain reaction analysis of the bodies of larvae revealed that cyp19A1 expression increased before the appearance of the first histological signs of ovarian differentiation at the feminizing temperature but remained low at the masculinizing temperature. The expression levels at mixed-sex producing temperatures were bimodal rather than intermediate, showing low and high modal values similar to those at the feminizing and masculinizing temperatures, respectively. The population percentages of high and low expression levels at intermediate temperatures were proportional to the percentage of females and males, respectively, and high levels were first observed at about the time of sex differentiation of females. These results suggest that cyp19A1 is involved in the process of ovarian formation and possibly also in the TSD of pejerrey.

Tissue- and sex-specific regulation of CYP19A1 expression in the Atlantic croaker (Micropogonias undulatus)

To better define the tissue- and sex-specific roles of aromatase in fishes, we have isolated a CYP19A1 cDNA sequence from a well-developed model of teleost reproduction, the Atlantic croaker (Micropogonias undulatus). This cDNA encodes a protein which has high identity (57-90%) to known CYP19A1 proteins and segregates with teleost CYP19A1 proteins in molecular phylogenetic analysis. In both sexes, the gene encoding Atlantic croaker CYP19A1 is expressed primarily in gonadal tissue, but also in the brain and other tissues at much lower levels, as determined relative to ribosomal 18S RNA expression by real-time quantitative RT-PCR. In females, the highest levels of CYP19A1 mRNA are found in the developing ovary compared to spawning, regressing and resting ovaries. In contrast, testicular CYP19A1 expression is lowest in developing testes and increases in spawning and regressing testes, although there were no statistically significant differences between stages. Brain CYP19A1 mRNA levels are lower in animals with developing gonads compared to spawning fish. In vitro treatment with human chorionic gonadotropin (10 IU/ml) for 6 or 24h increases CYP19A1 mRNA approximately 16- and 43-fold, respectively, in isolated Atlantic croaker ovarian follicles, but has no effect on CYP19A1 mRNA in testicular or brain minces. Six hour in vitro treatment with sex steroids (estradiol, testosterone or 17,20 beta,21-trihydroxy-4-pregnen-3-one; 290 nM) does not alter CYP19A1 mRNA in ovary, testis or brain. The regulation of CYP19A1 in the Atlantic croaker therefore differs in a tissue- and sex-specific manner.

Development and optimization of a Q-RT PCR method to quantify CYP19 mRNA expression in testis of male adult Xenopus laevis: Comparisons with aromatase enzyme activity

Due to limitations of the currently used enzymatic assays, it is difficult to determine aromatase activity in testicular tissue of amphibians. Quantitative reverse transcription polymerase chain reaction (Q-RT PCR) is a sensitive and reliable technique to detect low amounts of mRNA for specific genes. This study was designed to develop and optimize a SYBR Green I-based Q-RT PCR method to quantify CYP19 mRNA in testicular tissue from male Xenopus laevis. Four quantification methods for measuring CYP19 mRNA expression were compared. The established test system proved to be highly sensitive (detectable mRNA copies < 10), reproducible (interassay CV < 5.4%, intraassay CV < 0.9%), precise and specific for the CYP19 gene. To confirm the validity of the applied test system, an ex vivo testicular and ovarian explant study with a known inducer of aromatase, forskolin, was conducted. Forskolin induced CYP19 gene expression in both ovarian (3.7-fold) and testicular (2.6-fold) explants. Of the four quantification methods, the absolute standard curve and the comparative CT method appear to be optimal as indicated by their highly significant correlation (r2 = 0.998, p < 0.001). In conclusion, we recommend the comparative CT method over the standard curve method because it is more economical in terms of both cost and labor. Although both aromatase activity and CYP19 mRNA were clearly detectable in testes of X. laevis, both aromatase enzyme activity and CYP19 gene expression were very low. Also, no significant relationships were found between aromatase enzyme activity and gene expression. This is likely due the fact that the aromatase enzyme may have been dormant at the developmental stage the frogs were in during the experiment.

Up-regulation of P450arom and down-regulation of Dmrt-1 genes in the temperature-dependent sex reversal from genetic males to phenotypic females in a salamander

When larvae of the salamander Hynobius retardatus were reared at a high temperature (28 degrees C) during their thermosensitive period (TSP=15-30 days after hatching), all larvae developed to phenotypic females irrespective of their genetic sexes. Hynobius P450 aromatase (P450arom) and Dmrt-1 complementary DNAs were isolated and their expression patterns were analyzed by competitive and conventional reverse transcriptase-polymerase chain reaction. While the P450arom gene was expressed predominantly in the ovary, Dmrt-1 was expressed exclusively in the testis. When larvae were reared at the female-producing temperature (28 degrees C) during the TSP, a strong expression of the P450arom gene and a complete suppression of the Dmrt-1 gene were induced in all experimental larvae. Up-regulation of the P450arom gene and down-regulation of the Dmrt-1 gene even in genetic males constitute a part of the molecular biological cascade for the temperature-dependent sex reversal from genetic males to phenotypic females in this salamander.