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.

日本鹌鹑 ( Coturnix japonica ) 是一种鸟类模型，用于评估化学品的生殖和发育毒性。日本国家环境研究所 (NIES) 建立了一个日本鹌鹑品系 NIES-L，由于其高度近交的特性，它可能是一个更好的模型。为了了解生殖器官的性别分化以及使用 NIES-L 鹌鹑进行禽类毒性评估的价值，我们通过酶联免疫吸附测定分析了雌二醇和雄激素血浆水平；性腺、苗勒管、沃尔夫管中雌激素受体-α (ERα)、ERβ 和雄激素受体 (AR) 的 mRNA 水平；和类固醇生成酶、胆固醇侧链裂解酶 (P450 _scc )、17α-羟化酶/C _{17-20的 mRNA 水平}裂解酶 (P450 _{17α, lyase} )、3β-羟基类固醇脱氢酶 (3β-HSD)、17β-羟基类固醇脱氢酶 (17β-HSD) 和芳香酶 (P450 _arom )、抗苗勒管激素 (AMH) 和 2 型 AMH 受体 (AMHR2 ) 在 NIES-L 日本鹌鹑胚胎第 9、12 和 15 天的性腺中，使用实时定量 PCR 方法。在这些胚胎时期，女性血浆雌二醇浓度高于男性，但血浆雄激素中未发现性别差异。所有检查的类固醇生成酶的 mRNA 水平在女性胚胎中显着高于男性胚胎。特别是，P450 _arom mRNA 水平显示出显着的性别差异：P450 _arom在雌性而非雄性性腺中表达。相比之下，男性性腺中的 AMH 和 AMHR2 mRNA 水平高于女性。ERα、ERβ和AR mRNA水平在左侧雌性性腺中升高，并在胚胎第15天达到峰值，但在左右雄性性腺中没有；因此，存在女性偏见的性别差异。雌性左侧苗勒管中的 ERα、ERβ 和 AR mRNA 水平增加，但在右侧苗勒管中不增加，并在胚胎第 15 天达到峰值，导致 mRNA 水平不对称。Wolffian 导管在两性中均表达 ERα、ERβ 和 AR，未发现性别差异或 mRNA 水平不对称。本研究获得的信息有助于阐明生殖器官有性二态性形成的分子内分泌学基础，并阐明 NIES-L 鹌鹑在毒性评估中的价值。