Villalpando I, Sánchez-Bringas G, Sánchez-Vargas I, Pedernera E, Villafán-Monroy H
Departamento de Biología Celular, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónma de Méxica, México.
Gen Comp Endocrinol. 2000 Mar;117(3):325-34. doi: 10.1006/gcen.2000.7425.
Steroid hormones appear to play an important role in gonadal sex differentiation of birds. Here we studied the steady-state level of the P450 arom mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) in the left and the right presumptive ovary and testis of developing chicken embryos. The gonads were evaluated every hour during the undifferentiated period, at 144-156 h of incubation (h/i), and every 24 h after sexual differentiation at 168 and 192 h/i. Activity of P450 arom was determined by estrone production from [3H]androstenedione at 144-192 h/i. Moreover, morphological development of the gonad was also examined by light microscopy. Results show that onset of P450 arom mRNA and its protein activity were simultaneously detected in the left and the right ovaries at 147 h/i. Asymmetric function of P450 arom gene expression was observed at 156 h/i when morphological gonadal differentiation is first recognized. Biotransformation of [3H]androstenedione to estrone was also asymmetrically detected between the left and right gonad at 156 h/i and asymmetry was maintained throughout the analyzed stages. It is proposed that there is a gene in birds that is asymmetrically expressed in the undifferentiated stage of the female and the male gonad. In the female this gene could promote P450 arom gene expression, increasing estrogen production, which in turn could induce ovarian cortex proliferation and expression of other structural estrogen-regulated genes involved in ovarian sexual determination.
类固醇激素似乎在鸟类性腺性别分化中发挥重要作用。在此，我们通过逆转录聚合酶链反应（RT-PCR）研究了发育中的鸡胚左右假定卵巢和睾丸中P450芳香化酶mRNA的稳态水平。在未分化期，即孵化144 - 156小时（h/i）期间，每小时对性腺进行评估，在168和192 h/i性分化后每24小时评估一次。通过在144 - 192 h/i时由[3H]雄烯二酮生成雌酮来测定P450芳香化酶的活性。此外，还通过光学显微镜检查了性腺的形态发育。结果表明，在147 h/i时，在左右卵巢中同时检测到P450芳香化酶mRNA及其蛋白活性。在156 h/i首次识别出性腺形态分化时，观察到P450芳香化酶基因表达的不对称功能。在156 h/i时，左右性腺之间[3H]雄烯二酮向雌酮的生物转化也检测到不对称，并且在整个分析阶段都保持不对称。有人提出，鸟类中存在一种基因，在雌性和雄性性腺的未分化阶段不对称表达。在雌性中，该基因可促进P450芳香化酶基因表达，增加雌激素生成，进而可诱导卵巢皮质增殖以及参与卵巢性别决定的其他受雌激素调节的结构基因的表达。
