Temperature--Not Chromosomes--Determines the Gender of Certain Lower Vertebrates

在许多产卵爬行动物中，卵的孵化温度决定了后代的性别，这一过程被称为温度依赖性性别决定（TSD）。温度如何刺激和抑制基因级联反应，以确定性腺性别和通道性发育是这个应用程序的重点。PI的工作假设是，孵化温度改变了胚胎的内分泌微环境，使得类固醇激素作为性别决定的最接近的触发器。该实验室已经开发了红耳滑龟作为动物模型系统，并证明雄性和雌性性腺发育是受类固醇，类固醇增强分子和类固醇干扰分子影响的独立途径。雌性决定是由雌激素引起的，而雄性决定是由不可芳香化的雄激素引起的。 实验旨在确定温度是否通过作用于编码类固醇激素受体和aromafast（一种关键的类固醇生成酶）的基因来完成性别决定。PI将继续芳香酶的克隆和测序。为了确定在性别决定的关键时期所选特定基因的表达和转录调控模式，PI将在温度敏感期开始、期间和之后的原位杂交和核糖核酸酶保护试验中利用雌激素受体和芳香酶的同源反义探针。 通过孵育温度、外源激素和其他试剂操纵TSD物种性别的能力提供了无与伦比的实验控制，从而能够比其他具有性染色体的脊椎动物物种更详细地分析性别决定期间基因表达的正常模式。除了触发因素，具有基因型性别决定的脊椎动物和具有TSD的脊椎动物之间的性别决定级联似乎是相似的。关于TSD的工作引起了人们的注意，温度和类固醇激素在脊椎动物的性发育中起着关键作用，因此有几个原因很重要。首先，长期以来一直认为母体或胚胎来源的类固醇激素不参与哺乳动物和鸟类性腺的形成。对TSD爬行动物的研究表明，这一结论可能为时过早。第二，由于TSD可能代表性染色体的进化前体，潜在的温度和类固醇的性别决定的影响可能存在，但部分或全部掩盖，在恒温动物。第三，温度还没有得到充分的研究，作为一个因素，类固醇激素的作用，恒温动物，尽管许多研究记录如何激素的反应和激素的作用显着依赖于温度。

In many egg-laying reptiles, the incubation temperature of the egg determines the sex of the offspring, a process known as temperature-dependent sex determination (TSD). How temperature both stimulates and inhibits genetic cascades to determine gonadal sex and channel sexual development is the focus of this application. The PI's working hypothesis is that incubation temperature modifies the endocrine microenvironment of the embryo such that steroid hormones serve as the proximate trigger for sex determination. This laboratory has developed the red-eared slider turtle as an animal model system and demonstrated that male and female gonadal development are separate pathways influenced by steroids, steroid-augmenting molecules, and steroid-interfering molecules. Female determination is caused by estrogens whereas male determination is caused by nonaromatizable androgens. Experiments are designed to determine if temperature accomplishes sex determination by acting on genes coding for steroid hormone receptors and aromafast, a key steroidogenic enzyme. The PI will continue the cloning and sequencing of the aromatase. To identify the patterns of expression and transcriptional regulation of selected specific genes during the critical periods of sex determination, the PI will utilize homologous antisense probes for estrogen receptor and aromatase of mENAs in in situ hybridization and ribonuclease protection assays at the beginning, during, and following the temperature-sensitive period. The ability to manipulate sex in TSD species by incubation temperature, exogenous hormones, and other agents provides unparalleled experimental control, thereby enabling more detailed analysis of the normal pattern of gene expression during sex determination than is possible with other amniote vertebrate species having sex chromosomes. Except for the trigger, the sex determining cascade appears to be similar between vertebrates having genotypic sex determination and those with TSD. The work on TSD draws attention t o the fact that temperature and steroid hormones can play a pivotal role in sexual development in an amniote vertebrate and is thus important for several reasons. First, it has long been assumed that steroid hormones of maternal or embryonic origin are not involved in gonad formation in mammals and birds. The work with TSD reptiles indicates that this conclusion may be premature. Second, since TSD may represent the evolutionary precursor to sex chromosomes, potential temperature and steroid effects in sex determination may be present, but partly or wholly masked, in homeotherms. Third, temperature has not been adequately investigated as a factor in steroid hormone action in homeotherms despite numerous studies documenting how both hormone responsiveness and hormone action are markedly dependent on temperature.