Effects of estrogens on sex differentiation in Japanese quail and chicken

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.

In ovo o,p'-DDT exposure induces malformation of reproductive organs and alters the expression of genes controlling sexual differentiation in Japanese quail embryo

In ovo exposure to o,p'-dichloro-diphenyl-trichloroethane (o,p'-DDT) impairs reproduction by inducing malformation of the reproductive organs in birds, although the mechanism remains unclear. Here, we examined the effects of o,p'-DDT on the development of the reproductive organs, the expression of genes controlling sexual differentiation, and the plasma concentrations of testosterone and estradiol in Japanese quail embryos. o,p'-DDT-containing sesame oil was injected into the yolk sac on Embryonic Day (E) 3 at a dose of 500, 2,000, or 8,000 μg per egg. On E15, the reproductive organs were observed; the gonads and Müllerian ducts (MDs) were sampled to measure the mRNA of steroidogenic enzymes, sex steroid receptors, anti-Müllerian hormone (AMH), and AMH receptor 2 (AMHR2); blood samples were collected to assay plasma testosterone and estradiol levels; and the gonads were used for histological analysis. o,p'-DDT dose-dependently increased the prevalence of hypertrophic MDs in females and residual MDs in males. In female MDs, o,p'-DDT dose-dependently decreased estrogen receptor (ER) α, ERβ, and AMHR2 mRNA expression. o,p'-DDT dose-dependently induced left-biased asymmetry of testis size, and ovary-like tissue was found in the left testis after exposure to 8,000 μg per egg o,p'-DDT, although asymmetric gene expression did not occur. o,p'-DDT did not affect ovarian tissue but did decrease 17α-hydroxylase/C17-20 lyase mRNA expression and dose-dependently increased ERβ mRNA expression. o,p'-DDT decreased plasma testosterone concentrations in females. These findings suggest that o,p'-DDT induces hypertrophy of the MDs and ovarian tissue formation in the left testis. Abnormal MD development may be linked to altered gene expression for sensing estrogens and AMH signals.

No effects of the antiandrogens cyproterone acetate (CPA), flutamide and p,p'-DDE on early sexual differentiation but CPA-induced retardation of embryonic development in the domestic fowl (Gallus gallus domesticus)

Because a wide range of environmental contaminants are known to cause endocrine disorders in humans and animals, in vivo tests are needed to identify such endocrine disrupting chemicals (EDCs) and to assess their biological effects. Despite the lack of a standardized guideline, the avian embryo has been shown to be a promising model system which responds sensitively to EDCs. After previous studies on the effects of estrogenic, antiestrogenic and androgenic substances, the present work focuses on the effects of in ovo exposure to p,p'-DDE, flutamide and cyproterone acetate (CPA) as antiandrogenic model compounds regarding gonadal sex differentiation and embryonic development of the domestic fowl (Gallus gallus domesticus). The substances were injected into the yolk of fertilized eggs on embryonic day one. On embryonic day 19 sex genotype and phenotype were determined, followed by gross morphological and histological examination of the gonads. Treatment with flutamide (0.5, 5, 50 µg/g egg), p,p'-DDE (0.5, 5, 50 µg/g egg) or CPA (0.2, 2, 20 µg/g egg) did not affect male or female gonad development, assessed by gonad surface area and cortex thickness in both sexes and by the percentage of seminiferous tubules in males as endpoints. This leads to the conclusion that antiandrogens do not affect sexual differentiation during embryonic development of G. gallus domesticus, reflecting that gonads are not target organs for androgens in birds. In ovo exposure to 2 and 20 µg CPA/g egg, however, resulted in significantly smaller embryos as displayed by shortened lengths of skull, ulna and tarsometatarsus. Although gonadal endpoints were not affected by antiandrogens, the embryo of G. gallus domesticus is shown to be a suitable test system for the identification of substance-related mortality and developmental delays.

Overview of Avian Sex Reversal

Sex determination and differentiation are processes by which a bipotential gonad adopts either a testicular or ovarian cell fate, and secondary sexual characteristics adopt either male or female developmental patterns. In birds, although genetic factors control the sex determination program, sex differentiation is sensitive to hormones, which can induce sex reversal when disturbed. Although these sex-reversed birds can form phenotypes opposite to their genotypes, none can experience complete sex reversal or produce offspring under natural conditions. Promising evidence indicates that the incomplete sex reversal is associated with cell autonomous sex identity (CASI) of avian cells, which is controlled by genetic factors. However, studies cannot clearly describe the regulatory mechanism of avian CASI and sex development at present, and these factors require further exploration. In spite of this, the abundant findings of avian sex research have provided theoretical bases for the progress of gender control technologies, which are being improved through interdisciplinary co-operation and will ultimately be employed in poultry production. In this review, we provide an overview of avian sex determination and differentiation and comprehensively summarize the research progress on sex reversal in birds, especially chickens. Importantly, we describe key issues faced by applying gender control systems in poultry production and chronologically summarize the development of avian sex control methods. In conclusion, this review provides unique perspectives for avian sex studies and helps scientists develop more advanced systems for sex regulation in birds.

Fadrozole-mediated sex reversal in the embryonic chicken gonad involves a PAX2 positive undifferentiated supporting cell state

Gonadal sex differentiation among vertebrates involves divergent fates of a common group of progenitor cells present in both presumptive ovaries and testes. The first cell type to differentiate gives rise to pre-Sertoli cells in the testis, and pre-follicular cells in the ovary. These cells derive from a common lineage of so-called “supporting cells”. In birds and other egg-laying vertebrates, locally synthesised estrogen has a central role in ovarian development and influences the fate of these supporting cells. Manipulation of estrogen levels during embryonic development induces gonadal sex reversal, providing an experimental setting to evaluate the process of gonadal sex differentiation. Recently, we identified PAX2 as a novel marker of the undifferentiated supporting cell lineage in the chicken embryo, expressed in both sexes prior to overt gonadal sex differentiation. PAX2 expression is downregulated at the onset of gonadal sex differentiation in both males and females. The analysis of this undifferentiated supporting cell marker, together with Sertoli (male) and pre-granulosa (female) will enhance our understanding of supporting cell differentiation. Here we characterized the supporting cells differentiation process and identified undifferentiated supporting cells in estrogen-mediated sex reversal experiments. Female embryos treated with the aromatase inhibitor fadrozole developed into ovotestis, containing pre-granulosa cells, Sertoli cells and PAX2 positive undifferentiated supporting cells. In contrast, male embryos treated with 17β-estradiol showed no PAX2+ undifferentiated gonadal supporting cells. Fadrozole time-course as well as multiple dose analysis suggests that supporting cell transdifferentiation involves a dedifferentiation event into a PAX2+ undifferentiated supporting cell state, followed by a redifferentiation towards the opposite sex lineage.

Becoming female: Ovarian differentiation from an evolutionary perspective

Differentiation of the bipotential gonadal primordium into ovaries and testes is a common process among vertebrate species. While vertebrate ovaries eventually share the same functions of producing oocytes and estrogens, ovarian differentiation relies on different morphogenetic, cellular, and molecular cues depending on species. The aim of this review is to highlight the conserved and divergent features of ovarian differentiation through an evolutionary perspective. From teleosts to mammals, each clade or species has a different story to tell. For this purpose, this review focuses on three specific aspects of ovarian differentiation: ovarian morphogenesis, the evolution of the role of estrogens on ovarian differentiation and the molecular pathways involved in granulosa cell determination and maintenance.

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

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.

Stress and steroid interaction modulates expression of estrogen receptor alpha in the brain, pituitary, and testes of immature Gallus gallus domesticus

In nature, food availability stimulates hypothalamo-pituitary-gonadal (HPG) axis while its scarcity induces stress, which further stimulates hypothalamo-pituitary-adrenal (HPA) axis producing a detrimental effect on the avian reproductive physiology. The present experiment was designed to examine the interaction of stress like food restriction and estradiol on male reproductive physiology with special emphasis on estrogen receptor alpha (ERα) as these play crucial role in reproduction. To achieve this, 60 day old White Leghorn immature cockrels were taken and divided into four groups (n  =  8 per group). One group was provided with food and water ad libitum. Second group was food restricted (FR) for 9 h/day after 5 days, third and fourth were administered with estradiol benzoate (EB 0.5 mg/100g/day) for 12 days. Fourth group was FR for 9 h/day after 5 days of EB treatment till last day of experiment (EB + FR). Immunofluorescent localization of ERα was principally in the pre-optic area and paraventricular nuclei of hypothalamus and in anterior pituitary gland. ERα expression was highly reduced (from 40 AU to 20 AU) after FR in testis but it increased (50 AU) after EB administration, EB + FR reflects a diminishing pattern in the increment after EB. FR decreased plasma estradiol while EB increased it. Increased plasma corticosterone, hydrogen peroxide, malondialdehyde, and decreased anti-oxidant enzymes in brain and testis of all groups indicate oxidative stress in the HPG axis. The increased ERα after EB and a decrease with FR and EB + FR support their reproductive function. Estrogen and its receptor alpha are responsible for maintaining epithelial morphology but FR along with EB administration modulates the testicular development by significantly decreasing its size (p<.0001) and seminiferous tubules (p<.0001) and no sperm formation via highly reduced expression of ir-ERα in HPG axis. Our findings led us to conclude that stress like FR and estradiol induces testicular regression immature male chickens by modulating ir-ERα expression in the HPG axis thereby resulting in reduction in reproductive physiology.

Effect of estrogen and stress on estrogen receptor 1 in the HPG axis of immature male Gallus gallus domesticus: Involvement of anti-oxidant system

Estrogen plays a key role in the regulation of reproductive behavior and control of the neuroendocrine system in both males and females. However, excessive quantity of exogenous estrogen produces a deleterious effect on the male reproductive system. To elucidate the mechanism by which estrogen modulates its receptor alpha (ESR1) in immature chicken during stress the study has been undertaken. The experiment investigated the physiological changes in the abundance of ESR1 in brain, pituitary and testes of immature male chickens after stress like water restriction. Twenty four immature male chickens were randomly assigned into four groups. The control group was provided with food and water ad libitum, second was water restricted 9 h each day for seven days (WR), third was treated with estradiol benzoate (EB) and fourth group was treated with EB followed by water restriction during last seven days of treatment (EB + WR). EB was administered at a dose of 0.5 mg/100 g/day for 12 days. EB administration as well as WR increases both the H₂O₂ and Malondialdehyde levels indicating oxidative stress in brain as well as in testis. Plasma corticosterone significantly increased in all groups while estradiol significantly decreased after water restriction. ESR1 protein was detected by immuno-fluorescence predominantly in the pre-optic area of the hypothalamus, pituitary and testes after EB administration. EB administration increases ESR1 proteins abundantly in the Sertoli cells, Leydig cells, spermatogonia and spermatids while WR decreases it. The decline in ESR1 proteins after EB administration during stress appears to be mediated by interaction of estrogen with hypothalamo-pituitary-adrenal (HPA) axis. Therefore, the findings substantiate the fact that WR and EB treatment increase the stress and alter the anti-oxidant enzymes via its receptor ESR1 in the brain, pituitary and testis of immature chicks. Moreover, these findings highlight the effect of estradiol in male chicks causing stress which is disrupting the normal physiological feedback mechanism in hormone release and the expression of receptor ESR1 along the hypothalamo-pituitary-gonadal (HPG) axis.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While these compounds have been reported as reproductive toxicants, their effects may partially be attributed to metabolites. The aim of this study was to examine reproductive organ development in chicken embryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP; 100 µg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 µg/g egg). The mixture was designed within the EU project EDC-MixRisk based upon a negative association with anogenital distance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryos were exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) and dissected two days prior to anticipated hatching (embryonic day 19). No discernible effects were noted on reproductive organs in embryos exposed to the mixture. MBP-treated males exhibited retention of Müllerian ducts and feminization of the left testicle, while MBP-administered females displayed a diminished the left ovary. In the left testicle of MBP-treated males, mRNA expression of female-associated genes was upregulated while the testicular marker gene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstrate that MBP, but not the phthalate monoester mixture, disrupts both male and female reproductive organ development in an avian embryo model.

Gonadal and Endocrine Analysis of a Gynandromorphic Chicken

Birds have a ZZ male and ZW female sex chromosome system. The relative roles of genetics and hormones in regulating avian sexual development have been revealed by studies on gynandromorphs. Gynandromorphs are rare bilateral sex chimeras, male on one side of the body and female on the other. We examined a naturally occurring gynandromorphic chicken that was externally male on the right side of the body and female on the left. The bird was diploid but with a mix of ZZ and ZW cells that correlated with the asymmetric sexual phenotype. The male side was 96% ZZ, and the female side was 77% ZZ and 23% ZW. The gonads of this bird at sexual maturity were largely testicular. The right gonad was a testis, with SOX9+ Sertoli cells, DMRT1+ germ cells, and active spermatogenesis. The left gonad was primarily testicular, but with some peripheral aromatase-expressing follicles. The bird had low levels of serum estradiol and high levels of testosterone, as expected for a male. Despite the low percentage of ZW cells on that side, the left side had female sex-linked feathering, smaller muscle mass, smaller leg and spur, and smaller wattle than the male side. This indicates that these sexually dimorphic structures must be at least partly independent of sex steroid effects. Even a small percentage of ZW cells appears sufficient to support female sexual differentiation. Given the lack of chromosome-wide dosage compensation in birds, various sexually dimorphic features may arise due to Z-gene dosage differences between the sexes.

Effects of estrogens and antiestrogens on gonadal sex differentiation and embryonic development in the domestic fowl (Gallus gallus domesticus)

Since it is known that environmental contaminants have the potential to cause endocrine disorders in humans and animals, there is an urgent need for in vivo tests to assess possible effects of these endocrine disrupting chemicals (EDCs). Although there is no standardized guideline, the avian embryo has proven to be particularly promising as it responds sensitively to a number of EDCs preferentially impacting the reproductive axis. In the present study we examined the effects of in ovo exposure to fulvestrant and tamoxifen as antiestrogenic model compounds and co-exposure to both substances and the potent estrogen 17α-ethinylestradiol (EE₂) regarding sex differentiation and embryonic development of the domestic fowl (Gallus gallus domesticus). The substances were injected into the yolk of fertilized eggs on embryonic day 1. On embryonic day 19 sex genotype and phenotype were determined, followed by gross morphological and histological examination of the gonads. Sole EE₂-treatment (20 ng/g egg) particularly affected male gonads and resulted in an increased formation of female-like gonadal cortex tissue and a reduction of seminiferous tubules. In ovo exposure to tamoxifen (0.1/1/10 µg/g egg) strongly impaired the differentiation of female gonads, led to a significant size reduction of the left ovary and induced malformations of the ovarian cortex, while fulvestrant (0.1/1/10 µg/g egg) did not affect sexual differentiation. However, both antiestrogens were able to antagonize the feminizing effects of EE₂in genetic males when administered simultaneously. Since both estrogens and antiestrogens induce concentration-dependent morphological alterations of the sex organs, the chick embryo can be regarded as a promising model for the identification of chemicals with estrogenic and antiestrogenic activity.

Biphasic modulation of neuro- and interrenal steroidogenesis in juvenile African sharptooth catfish (Clarias gariepinus) exposed to waterborne di-(2-ethylhexyl) phthalate

Receptor (i.e. genomic) and non-receptor (or non-genomic) effects of endocrine toxicology have received limited or almost non-existent attention for tropical species and regions. In the present study, we have evaluated the effects of di-(2-ethylhexyl) phthalate (DEHP) on neuro- and interrenal steroidogenesis of the African catfish (Clarias gariepinus) using molecular, immunochemical and physiological approaches. Juvenile fish (mean weight and length: 5.6±0.6g and 8.2±1.2cm, respectively), were randomly distributed into ten 120L rectangular glass tanks containing 60L of dechlorinated tap water, at 50 fish per exposure group. The fish were exposed to environmentally relevant concentrations of DEHP, consisting of 0 (ethanol solvent control), 10, 100, 200, and 400μg DEHP/L water and performed in two replicates. Brain, liver and head kidney samples were collected at day 3, 7 and 14 after exposure, and analysed for star, p450scc, cyp19a1, cyp17, cyp11β-, 3β-, 17β- and 20β-hsd, and 17β-ohase mRNA expression using real-time PCR. The StAR, P450scc and CYP19 proteins were measured using immunoblotting method, while estradiol-17β (E2) and testosterone (T) were measured in liver homogenate using enzyme immunoassay (EIA). Our data showed a consistent and unique pattern of biphasic effect on star and steroidogenic enzyme genes with increases at low concentration (10μg/L) and thereafter, a concentration-dependent decrease in both the brain and head kidney, that paralleled the expression of StAR, P450scc and CYP19 proteins. Cellular E2 and T levels showed an apparent DEHP concentration-dependent increase at day 14 of exposure. The observed consistency in the current findings and in view of previous reports on contaminants-induced alterations in neuro- and interrenal steroidogenesis, the broader toxicological and endocrine disruptor implication of our data indicate potentials for overt reproductive, metabolic, physiological and general health consequences for the exposed organisms.

Expression of sex hormone receptors in the brain of male and female newly hatched chicks

Chromosomal sex and steroid hormones play a determining role in brain sexual differentiation during chick embryonic development. Hormone effects on the brain are associated with the expression pattern of their intracellular receptors, which is sexually dimorphic in many species. We determined by Western blot the content of progesterone, estrogen, and androgen receptors (PR-A and PR-B, ERα, and AR, respectively) in the cortex, cerebellum, tectum, and hypothalamus of female and male newly hatched chicks. Males presented a higher content of PR-B in the tectum whereas females exhibited a higher content of PR-A in the hypothalamus. ERα was only detected as a band of 66kDa, and it showed a higher content in the cerebellum and tectum of females as compared to these regions in males. Besides, males exhibited a higher content of AR in the tectum than females. Our study suggests that newly hatched chicks show a sexual dimorphism in the expression of sex hormone receptors in brain regions involved in sexual behavior such as the hypothalamus, and in non-sexual behavior such as the optic tectum and the cerebellum.

Critical developmental windows for morphology and hematology revealed by intermittent and continuous hypoxic incubation in embryos of quail (Coturnix coturnix)

Hypoxia during embryonic growth in embryos is frequently a powerful determinant of development, but at least in avian embryos the effects appear to show considerable intra- and inter-specific variation. We hypothesized that some of this variation may arise from different protocols that may or may not result in exposure during the embryo’s critical window for hypoxic effects. To test this hypothesis, quail embryos (Coturnix coturnix) in the intact egg were exposed to hypoxia (~15% O₂) during “early” (Day 0 through Day 5, abbreviated as D0-D5), “middle” (D6-D10) or “late” (D11-D15) incubation or for their entire 16–18 day incubation (“continuous hypoxia”) to determine critical windows for viability and growth. Viability, body mass, beak and toe length, heart mass, and hematology (hematocrit and hemoglobin concentration) were measured on D5, D10, D15 and at hatching typically between D16 and D18 Viability rate was ~50–70% immediately following the exposure period in the early, middle and late hypoxic groups, but viability improved in the early and late groups once normoxia was restored. Middle hypoxia groups showed continuing low viability, suggesting a critical period from D6-D10 for embryo viability. The continuous hypoxia group experienced viability reaching <10% after D15. Hypoxia, especially during late and continuous hypoxia, also inhibited growth of body, beak and toe when measured at D15. Full recovery to normal body mass upon hatching occurred in all other groups except for continuous hypoxia. Contrary to previous avian studies, heart mass, hematocrit and hemoglobin concentration were not altered by any hypoxic incubation pattern. Although hypoxia can inhibit embryo viability and organ growth during most incubation periods, the greatest effects result from continuous or middle incubation hypoxic exposure. Hypoxic inhibition of growth can subsequently be “repaired” by catch-up growth if a final period of normoxic development is available. Collectively, these data indicate a critical developmental window for hypoxia susceptibility during the mid-embryonic period of development.

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.

Cloning, Characterization, and Expression Profile of Estrogen Receptor in Common Chinese Cuttlefish, Sepiella japonica

Sex steroid hormones are widely detected in molluscs and play important roles in sex determination, gonadal tissue maturation, and gametogenesis. Nevertheless, the signaling pathways of sex steroids in cephalopod have not yet been clearly elucidated. In the present study, a full-length sequence encoding the estrogen receptor (ER) was isolated from common Chinese cuttlefish, Sepiella japonica. The sjER cDNA clone was found to contain 1,788 nucleotides including a 1,470 bp open reading frame encoding 489 amino acid (aa) residues. The deduced ER protein consisted of six nuclear receptor characteristic domains. Based on a phylogenetic analysis, the ER DNA-binding domain and ligand-binding domain are highly conserved compared to other mollusc ERs. Highest aa identities were found for sjER with common octopus (Octopus vulgaris) ER (89%) and pacific oyster (Crassostrea gigas) ER (61%). Tissue expression analysis confirmed that sjER was widely distributed among tissues and predominantly expressed in the brain, liver, gonad (testis and ovary), and other accessory sexual gland (nidamental gland). The ER expression was temporally upregulated in the brain, liver, and ovary during the early sexual maturation period in S. japonica, which is coincident with the fluctuation of ovary estradiol content. These suggest that sjER may be involved in regulating the reproductive cycle of S. japonica. A fusion protein transient transfections assay showed that sjER was mainly located in the nucleus, suggesting a possible orthodox working mechanism of S. japonica ER in the nucleus through a ligand-dependent activation of specific gene transcription.

Selection of the Inducer for the Differentiation of Chicken Embryonic Stem Cells into Male Germ Cells In Vitro

Several inducers have been used to differentiate embryonic stem cells (ESCs) into male germ cells but the induction process has been inefficient. To solve the problem of low efficiency of inducer for ESCs differentiation into male germ cells, all-trans retinoic acid (ATRA), Am80(the retinoic acid receptor agonist), and estradiol (E2) was used to induce ESCs to differentiate into male germ cells in vitro. ESCs were cultured in media containing ATRA, Am80, or E2 respectively which can differentiate ESCs into a germ cell lineage. In process of ATRA and Am80 induction Group, germ cell-like cells can be observed in 10 days; but have no in E2 induction Group. The marker genes of germ cell: Dazl, Stra8, C-kit, Cvh, integrinα6, and integrinβ1 all showed a significant up-regulation in the expression level. The ATRA-induction group showed high expression of C-kit and Cvh around 4 days, and integrinα6 and integrinβ1 were activated on day 10, respectively, while the E2-,Am80- induction group showed a high expression of C-kit as early as 4 days immunocytochemistry results shown that, integrinα6 and integrinβ1 could be detected in the ATRA-, Am80-, and E2-induction group, Positive clones in the ATRA group were greater in number than those in the other two groups. we conclued that ATRA, Am80, and E2 can promote the expression of the corresponding genes of germ cells, and had different effect on the differentiation of ESCs into male germ cells. ATRA was the most effective inducer of germ cell differentiation.

Novel Polymorphisms of Adrenergic, Alpha-1B-, Receptor and Peroxisome Proliferator-activated Receptor Gamma, Coactivator 1 Beta Genes and Their Association with Egg Production Traits in Local Chinese Dagu Hens

Adrenergic, alpha-1B-, receptor (ADRA1B) and peroxisome proliferator-activated receptor gamma, coactivator 1 beta (PPARGC1B) genes are involved in regulation of hen ovarian development. In this study, these two genes were investigated as possible molecular markers associated with hen-housed egg production, egg weight (EW) and body weight in Chinese Dagu hens. Samples were analyzed using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique, followed by sequencing analysis. Two novel single nucleotide polymorphisms (SNPs) were identified within the candidate genes. Among them, an A/G transition at base position 1915 in exon 2 of ADRA1B gene and a T/C mutation at base position 6146 in the 3′-untranslated region (UTR) of PPARGC1B gene were found to be polymorphic and named SNP A1915G and T6146C, respectively. The SNP A1915G (ADRA1B) leads to a non-synonymous substitution (aspartic acid 489-to-glycine). The 360 birds from the Dagu population were divided into genotypes AA and AG, allele A was found to be present at a higher frequency. Furthermore, the AG genotype correlated with significantly higher hen-housed egg production (HHEP) at 30, 43, 57, and 66 wks of age and with a higher EW at 30 and 43 wks (p<0.05). For the SNP T6146C (PPARGC1B), the hens were typed into TT and TC genotypes, with the T allele shown to be dominant. The TC genotype was also markedly correlated with higher HHEP at 57 and 66 wks of age and EW at 30 and 43 wks (p<0.05). Moreover, four haplotypes were reconstructed based on these two SNPs, with the AGTC haplotype found to be associated with the highest HHEP at 30 to 66 wks of age and with higher EW at 30 and 43 wks (p<0.05). Collectively, the two SNPs identified in this study might be used as potential genetic molecular markers favorable in the improvement of egg productivity in chicken breeding.

Differential expression of estrogen receptor alpha in the embryonic adrenal-kidney-gonadal complex of the oviparous lizard, Calotes versicolor (Daud.)

Estrogen signalling is critical for ovarian differentiation in reptiles with temperature-dependent sex determination (TSD). To elucidate the involvement of estrogen in this process, adrenal-kidney-gonadal (AKG) expression of estrogen receptor (ERα) was studied at female-producing temperature (FPT) in the developing embryos of the lizard, Calotes versicolor which exhibits a distinct pattern of TSD. The eggs of this lizard were incubated at 31.5±0.5°C (100% FPT). The torso of embryos containing adrenal-kidney-gonadal complex (AKG) was collected during different stages of development and subjected to Western blotting and immunohistochemistry analysis. The ERα antibody recognized two protein bands with apparent molecular weight ∼55 and ∼45kDa in the total protein extracts of embryonic AKG complex of C. versicolor. The observed results suggest the occurrence of isoforms of ERα. The differential expression of two different protein isoforms may reveal their distinct role in cell proliferation during gonadal differentiation. This is the first report to reveal two isoforms of the ERα in a reptile during development. Immunohistochemical studies reveal a weak, but specific, cytoplasmic ERα immunostaining exclusively in the AKG during late thermo-sensitive period suggesting the responsiveness of AKG to estrogens before gonadal differentiation at FPT. Further, cytoplasmic as well as nuclear expression of ERα in the medulla and in oogonia of the cortex (faint activity) at gonadal differentiation stage suggests that the onset of gonadal estrogen activity coincides with sexual differentiation of gonad. Intensity and pattern of the immunoreactions of ERα in the medullary region at FPT suggest endogenous production of estrogen which may act in a paracrine fashion to induce neighboring cells into ovarian differentiation pathway.

The effects on steroidogenesis and histopathology of adult male Japanese quails (Coturnix coturnix japonica) testis following pre-pubertal exposure to di(n-butyl) phthalate (DBP)

In the present study, we have investigated the effects of 30-day dietary (pre-pubertal) exposure to different doses (0 (control), 1, 10, 50, 200 and 400 mg/kg bodyweight/day) of di(n-butyl) phthalate (DBP) on Leydig cells of adult male Japanese quails by quantifying the transcript levels for P450 side-chain cleavage (p450scc), P450c17 (CYP17), and 3β- and 17β-hydroxysteroid dehydrogenase (hsd) using quantitative (real-time) polymerase chain reaction (qRT-PCR). In addition, the plasma testosterone levels were analysed using radioimmunoassay (RIA) and testis was examined for evidence of gross pathology and histopathology. Our data showed that pre-pubertal exposure to DBP produced alterations in testicular architecture as evident by poorly developed or mis-shaped testis, and altered spermatogenesis due to tubular degeneration and atrophy of seminiferous tubules especially in the high DBP dose (200 and 400 mg/kg) treated groups. In addition, DBP altered several key enzymes involved in testicular steroidogenesis pathways in an apparent dose-dependent manner. For example, biphasic effects of DBP were observed for P450scc and 3β-hsd mRNA, that were generally increasing at low dose 10 mg/kg, and thereafter, an apparent dose-dependent decrease between 50 and 400mg/kg. The steroidogenic acute regulatory (StAR) protein was at the lowest detectable limits and therefore not quantifiable. These effects did not parallel the non-significant changes observed for plasma testosterone levels. The present data is consistent with previous reports showing that DBP modulates Leydig cell steroidogenesis in several species, with a potential negative effect on reproduction in those avian species that are vulnerable to endocrine disrupting chemicals.

Microanatomical Study of Embryonic Gonadal Development in Japanese Quail (Coturnix japonica)

Gonadal development of quail embryos was examined histologically using histological and histochemical methods. In the present study, quail embryos were studied at various stages of incubation period based on phases of gonadogenesis. Germ cell migration was observed on day 3-4 but gonadal differentiation and gonadal function were observed on day 6-8 and day 11-14, respectively. During germ cell migration, quail primordial germ cells (qPGCs) were successfully detected in both left and right genital ridges as well as the dorsal mesentery by lectin histochemistry. Unexpectedly, qPGCs-like cells were found next to the neural tube by Mallory-AZAN stain. During gonadal differentiation, embryonic sex can be distinguished histologically since day 8 of incubation. Embryonic testis exhibited a thin cortex, whereas embryonic ovary exhibited a thick cortex. Testicular cord formation was found in the medulla of embryonic testes while the lacunae and fat-laden cells were found in the medulla of embryonic ovary during gonadal function. This is the first report on a comparison of phases of gonadogenesis and histochemical study of quail embryonic gonads in both sexes.

Environmental concentration of nonylphenol alters the development of urogenital and visceral organs in avian model

Nonylphenol (NP) is an endocrine disruptor with harmful effects including feminization and carcinogenesis on various organisms. This substance is a degradation product of nonylphenol ethoxylates (NPEO) that is used in several industrial and agricultural processes. In this paper, we examined the assessment of NP exposure on chick embryo development, using a concentration consistent with the environmental concentrations of NP. With this aim, NP (between 0.1 and 50 μg/egg) was injected into the yolk of egg through a small needle hole in the shell. We report the effect of NP on chick reproductive system development although the effect we observed is lower than those observed by exposition to other endocrine disruptors. However, histological analysis highlighted a decrease of intraluminal seminiferous surface area in 64.12% of case (P=0.0086) and an heterogeneous organization of the renal tubules when 10 μg/egg were injected. Moreover, an impairment of liver development with an abnormal bile spillage was observed when higher concentration of NP was injected (50 μg/egg).

Effect of estradiol-17β on follicle-stimulating hormone secretion and egg-laying performance of Japanese quail

The aim of this study was to measure the effect of estradiol-17β (E2) injection on follicle-stimulating hormone (FSH) secretion and egg-laying performance of Japanese quail. Female Japanese quail were housed in cages and fed ad libitum. After a 7-day adaptation period, the birds were randomly assigned to three groups, that is, one control group and two test groups. The birds were weighed, before every injection. The control group was subcutaneously injected with 0.2 ml sesame oil-ethanol mixture, whereas test groups were injected, twice in a week, with 0.2 ml sesame oil-ethanol mixture containing 0.1 or 0.2 mg E2 along the study. One day after the first injection, egg number, egg weight, eggshell strength and food conception were daily recorded. On the last day of the experiment, the birds were injected and 3 h later seven birds from each group were randomly selected for bleeding. Blood samples (2 ml/bird) were collected from the jugular vein for the measurements of serum concentrations of E2, FSH, calcium (Ca) and phosphorus (P). E2 injection did not cause any significant changes in serum FSH concentrations, daily egg laid/bird, food conception/bird, serum concentrations of the Ca and the P. Egg weight was significantly increased in the 0.1 mg E2-injected group as compared with the control and 0.2 mg E2-injected groups. Eggshell strength in the 0.2 mg E2-injected group was significantly high as compared with the control, whereas the difference between the 0.1 mg E2- and 0.2 mg E2-injected groups was not statistically important. These results show that serum FSH concentration was not increased even when slightly suppressed by subcutaneous injection of 0.1 or 0.2 mg E2. Different doses of E2 have different functions. The increase in BWs in the 0.1 mg E2-injected group was a result of the dose effect, which probably increased growth hormone secretion from the pituitary or IGF-1 synthesis from the liver or both. The dose, 0.2 mg E2, was ineffective in increasing the BW, but it significantly increased eggshell strength probably via the increase in Ca and P utilizations.

The effects of incubation temperature on the sex of Japanese quail chicks

The effects of incubation temperature on the sex of Japanese quail chicks were investigated in this study. The study was conducted on Japanese quail. In all, 4500 eggs obtained from 2 generations were used. At the beginning of the study, a new flock was formed from available hatching eggs. Hatching eggs were gathered at 3 different ages (8 to 10 weeks, 16 to 18 weeks and 22 to 24 weeks of age) from the laying period in this flock. These eggs were exposed to 5 different incubation temperatures (36.7, 37.2, 37.7, 38.2, and 38.7°C). The hatching results were evaluated for each group. Chicks obtained from these temperature groups were reared separately to obtain quail for breeding. Eggs for incubation were gathered from these breeding quail when they were between 15 and 18 weeks of age. These eggs were placed in an incubator at a standard (37.7°C) temperature, separated by F(1)-generation temperature groups. The chicks in all groups were reared separately, and the sex of the chicks was determined at maturity. Statistical differences (P < 0.05) were found for the sex of the chicks in the third group (22 to 24 weeks) of the F(1) generation, compared with other groups. This result confirmed the hypothesis that different incubation temperatures for the first generation (at the embryo stage) might influence the sex of the next generation of chicks. Further studies are needed to investigate the effects of incubation temperature on chicks from different perspectives.

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.

Occurrence and cellular distribution of estrogen receptors ERα and ERβ in the testis and epididymal region of roosters

Estrogen signaling is required for the maintenance of male reproductive function and is mediated by the estrogen receptors ERα and ERβ. These receptors are widely distributed in mammalian reproductive tissues, but information is limited in non-mammalian species including birds. The aim of this study was to investigate the occurrence and cellular distribution of ERα and ERβ in the testis and epididymal region of roosters. The results showed for the first time that ERβ was the predominant receptor detected in the testis, being expressed in the somatic and some germ cells. Within the epididymal region, ERβ was strongly expressed in all segments, whereas the most intense reaction for ERα was found in the distal efferent ductules. The differential expression of ERα and ERβ within the rooster testis and epididymal region suggests that these organs may be a target for different actions of estrogen.

Exposure to diethylstilbestrol during embryonic and larval stages of medaka fish (Oryzias latipes) leads to sex reversal in genetic males and reduced gonad weight in genetic females

Molecular and cellular mechanisms involved in artificially induced ovarian differentiation were analyzed by exposing embryos of medaka (Oryzias latipes) to a potent nonsteroidal estrogen, diethylstilbestrol (DES). Embryos were exposed for short-exposure (SE) [from 0 to 8 d postfertilization (dpf)] and long-exposure (LE) periods (from 0 to 18/28 dpf) to 1 ng/ml of DES, and status of sexual differentiation in somatic and germ cells of these gonads was analyzed at 8, 18, and 28 dpf by histology, cell proliferation assays, TUNEL assay, and in situ hybridization using sex-specific somatic and germ cell markers. Additionally, gonads of exposed fry were examined after withdrawal of DES to see whether effects of DES in exposed fish were reversible or not. DES induced germ cell proliferation and meiosis in XY fry of SE and LE groups. However, SE induced only a partial reduction in expression of gonadal soma-derived factor, the male-dominant somatic cell marker, and was not sufficient to induce ovarian development after withdrawal of DES. On the contrary, LE resulted in complete loss of such male-specific gene expression in somatic cells of XY gonads, and these gonads underwent sustained ovarian development even after withdrawal of DES. Importantly, LE to DES affected germ cell proliferation in XX gonads adversely during early stages of sexual differentiation, leading to reduced gonad weight in adulthood. Interestingly, apoptosis was not the cause for reduction in germ cell number. Taken together, these results indicated that DES exposure has long-lasting effects on the gonadal development in genetic males (sex reversal) and females (reduced gonad weight) of medaka.