Effects on differentiation of reproductive organs and sexual behaviour in Japanese quail by excessive embryonic ERalpha activation

Ethynylestradiol feminizes gene expression partly in testis developing as ovotestis and disrupts asymmetric Müllerian duct development by eliminating asymmetric gene expression in Japanese quail embryos

In avian embryos, xenoestrogens induce abnormalities in reproductive organs, particularly the testes and Müllerian ducts (MDs). However, the molecular mechanisms remain poorly understood. We investigated the effects of ethynylestradiol (EE2) exposure on gene expression associated with reproductive organ development in Japanese quail embryos. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis revealed that the left testis containing ovary-like tissues following EE2 exposure highly expressed the genes for steroidogenic enzymes (P450scc, P45017α, lyase, and 3β-HSD) and estrogen receptor-β, compared to the right testis. No asymmetry was found in these gene expression without EE2. EE2 induced hypertrophy in female MDs and suppressed atrophy in male MDs on both sides. RNA sequencing analysis of female MDs showed 1,366 differentially expressed genes between developing left MD and atrophied right MD in the absence of EE2, and these genes were enriched in Gene Ontology terms related to organogenesis, including cell proliferation, migration and differentiation, and angiogenesis. However, EE2 reduced asymmetrically expressed genes to 21. RT-qPCR analysis indicated that genes promoting cell cycle progression and oncogenesis were more highly expressed in the left MD than in the right MD, but EE2 eliminated such asymmetric gene expression by increasing levels on the right side. EE2-exposed males showed overexpression of these genes in both MDs. This study reveals part of the molecular basis of xenoestrogen-induced abnormalities in avian reproductive organs, where EE2 may partly feminize gene expression in the left testis, developing as the ovotestis, and induce bilateral MD malformation by canceling asymmetric gene expression underlying MD development.

Sexually dimorphic expression of sexual differentiation genes in the internal genital organs of Japanese quail embryos

Japanese quail (Coturnix japonica) is an avian model used to evaluate the reproductive and developmental toxicity of chemicals. The National Institute for Environmental Studies (NIES) of Japan established a strain of Japanese quail, NIES-L, which may be a better model because of its highly inbred characteristics. To understand sexual differentiation of the reproductive organs and the value of using NIES-L quails for avian toxicity assessment, we profiled estradiol and androgen plasma levels by enzyme-linked immunosorbent assay; the mRNA levels of estrogen receptor-α (ERα), ERβ, and androgen receptor (AR) in the gonads, Müllerian ducts, Wolffian ducts; and the mRNA levels of steroidogenic enzymes, cholesterol side chain cleavage enzyme (P450_scc), 17α-hydroxylase/C_17-20 lyase (P450_{17α, lyase}), 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD), and aromatase (P450_arom), anti-Müllerian hormone (AMH), and AMH receptor type 2 (AMHR2) in the gonads of NIES-L Japanese quails on embryonic days 9, 12, and 15 using a real-time quantitative PCR method. The plasma estradiol concentration was higher in females than males on these embryonic days, but no sex difference was found in the plasma androgens. The mRNA levels of all examined steroidogenic enzymes were significantly higher in female than male embryos. In particular, the P450_arom mRNA levels showed a striking sex difference: P450_arom was expressed in female but not male gonads. In contrast, the AMH and AMHR2 mRNA levels in the gonads were higher in males than females. The ERα, ERβ, and AR mRNA levels increased in the left female gonad and peaked on embryonic day 15, but not in the left and right male gonads; therefore, there was a female-biased sex difference. The ERα, ERβ, and AR mRNA levels in the left Müllerian duct, but not in the right Müllerian duct, of females increased and peaked on embryonic day 15, which resulted in asymmetric mRNA levels. The Wolffian ducts expressed ERα, ERβ, and AR in both sexes, and no sex difference or asymmetry of mRNA levels was found. The information obtained from this study helps elucidate the molecular endocrinological basis of sexual dimorphism formation of reproductive organs and clarify the value of NIES-L quails for toxicity assessment.

Key role of estrogen receptor β in the organization of brain and behavior of the Japanese quail

Estrogens play a key role in the sexual differentiation of the brain and behavior. While early estrogen actions exert masculinizing effects on the brain of male rodents, a diametrically opposite effect is observed in birds where estrogens demasculinize the brain of females. Yet, the two vertebrate classes express similar sex differences in the brain and behavior. Although ERα is thought to play a major role in these processes in rodents, the role of ERβ is still controversial. In birds, the identity of the estrogen receptor(s) underlying the demasculinization of the female brain remains unclear. The aim of the present study was thus to determine in Japanese quail the effects of specific agonists of ERα (propylpyrazole triol, PPT) and ERβ (diarylpropionitrile, DPN) administered at the beginning of the sensitive period (embryonic day 7, E7) on the sexual differentiation of male sexual behavior and on the density of vasotocin-immunoreactive (VT-ir) fibers, a known marker of the organizational action of estrogens on the quail brain. We demonstrate that estradiol benzoate and the ERβ agonist (DPN) demasculinize male sexual behavior and decrease the density of VT-ir fibers in the medial preoptic nucleus and the bed nucleus of the stria terminalis, while PPT has no effect on these measures. These results clearly indicate that ERβ, but not ERα, is involved in the estrogen-induced sexual differentiation of brain and sexual behavior in quail.

Effects of selective and combined activation of estrogen receptor α and β on reproductive organ development and sexual behaviour in Japanese quail (Coturnix japonica)

Excess estrogen exposure of avian embryos perturbs reproductive organ development in both sexes and demasculinizes the reproductive behaviors of adult males. We have previously shown that these characteristic effects on the reproductive organs also can be induced by exposure of Japanese quail (Coturnix japonica) embryos to selective agonists of estrogen receptor alpha (ERα). In contrast, the male copulatory behavior is only weakly affected by developmental exposure to an ERα agonist. To further elucidate the respective roles of ERα and ERβ in estrogen-induced disruption of sexual differentiation, we exposed Japanese quail embryos in ovo to the selective ERα agonist 16α-lactone-estradiol (16αLE₂), the selective ERβ agonist WAY-200070, or both substances in combination. The ERα agonist feminized the testes in male embryos and reduced cloacal gland size in adult males. Furthermore, anomalous retention and malformations of the Müllerian ducts/oviducts were seen in embryos and juveniles of both sexes. The ERβ agonist did not induce any of these effects and did not influence the action of the ERα agonist. Male copulatory behavior was not affected by embryonic exposure to either the ERα- or the ERβ-selective agonist but was slightly suppressed by treatment with the two compounds combined. Our results suggest that the reproductive organs become sexually differentiated consequent to activation of ERα by endogenous estrogens; excessive activation of ERα, but not ERβ, during embryonic development may disrupt this process. Our results also suggest that the demasculinizing effect of estrogens on male copulatory behavior is only partly mediated by ERα and ERβ, and may rather involve other estrogen-responsive pathways.

In ovo exposure to nonylphenol and bisphenol A resulted in dose-independent feminization of male gonads in Japanese quail (Coturnix japonica) embryos

Sex reversal effects of nonylphenol and bisphenol A on the gonads in F(1) (AWE × WE) Japanese quail (Coturnix japonica) embryos were investigated using an in vivo screening model developed previously. The F(1) (AWE × WE) Japanese quail are a useful avian model because sex differentiation is confirmed by the plumage color before hatching, ruled by a criss-cross inheritance. The nonylphenol at 200, 2,000, 20,000, and 200,000 ng/egg and bisphenol A at 20, 200, 2,000, and 20,000 ng/egg were injected into the egg white just before incubation. At 16 d of incubation, embryos were subjected to a complete necropsy, and their gonads were both grossly observed and examined histopathologically and morphometrically. Grossly, genetic sex was confirmed because plumage color coincided completely with the external sex phenotype of the gonads in all embryos. Histopathologically, feminization of the male gonad, called ovotestis, developed in the left testis in all nonylphenol- and bisphenol A-treated groups. The incidence of the lesion in all treated groups was significantly higher than that in the control group, whereas there were no dose-dependent changes in the incidence and area of the ovotestis in both nonylphenol- and bisphenol A-treated groups. The present study revealed that nonylphenol and bisphenol A have a dose-independent potential of ovotestis induction in the Japanese quail embryo.

Activation of estrogen receptor alpha disrupts differentiation of the reproductive organs in chicken embryos

Gonadal estrogen plays an important role in the differentiation of a female phenotype in birds. Exogenous compounds that interfere with estrogen signaling, for instance by binding to the estrogen receptors alpha and beta (ERα and ERβ), are therefore potential disruptors of sexual differentiation in birds. The ERα agonist propyl-pyrazole-triol (PPT), the ERα antagonist methyl piperidino pyrazole (MPP) and the ERβ agonist diarylproprionitrile (DPN) were used in the present study to explore the roles of the ERs in normal and disrupted sex differentiation in the chicken embryo. Activation of ERα by PPT caused disturbed differentiation of the reproductive organs in both sexes. In male embryos, PPT caused left-side ovotestis formation and retention of the Müllerian ducts. In female embryos, PPT caused retention of the right Müllerian duct (which normally regresses) and malformation of both Müllerian ducts. PPT also induced hepatic expression of mRNA for the estrogen-regulated egg yolk protein apoVLDL II. Notably, none of these effects were observed following treatment with DPN. ERα-inactivation by MPP counteracted the action of PPT but had little effect by its own. Our results indicate that ERα plays an important role in sex differentiation of the reproductive tract in female chicken embryos and show that ERα can mediate xenoestrogen-induced disturbances of sex differentiation.