Responsiveness of sex determination to thermal cues and maternal estrogens as potential modifiers

大多数生物对环境温度有反应，这些反应通常是通过比较处于一个温度下的个体和处于不同温度下的个体来研究的。这种方法忽略了两个重要的点：1)自然界的温度通常是可变的，暴露在给定的温度下可能是短暂的；2)它在量化个体对温度做出反应所需时间的变化方面做得很差。这个项目的重点是理解为什么有些人对短时间暴露在给定温度下有反应，而另一些人则没有。研究将使用红耳滑龟（Trachemys scripta）进行，其中孵化温度影响性别决定，这提供了个体如何对温度做出反应的明确信号（即睾丸或卵巢的形成）。具体来说，较低的孵育温度可诱导睾丸发育，较暖的孵育温度可诱导卵巢发育。研究还证实，卵子中较高水平的雌激素会增加胚胎发育卵巢的可能性。在自然条件下，胚胎通常会经历睾丸和卵巢的诱导温度，因此研究的目的是破译在温暖的温度下暴露多长时间才能诱导卵巢发育，以及雌激素水平升高是否会降低暴露需求。加深我们对温度如何影响性别决定的理解将有助于减轻气候变化对热敏物种的影响。该项目将培养一名博士后研究员、研究生和本科生，并将让大学预科学生参与stem相关活动。最近的研究表明，温度依赖性的性别决定涉及决定性别的关键转录因子的表观遗传调控。在红耳滑龟（Trachemys scripta）中，组蛋白去甲基化酶Kdm6b去除Dmrt1启动子上的抑制性组蛋白标记，Dmrt1是睾丸发育的保守调节因子。对于这个物种，睾丸发育在较低的孵育温度（低于29˚C）下诱导。本提案探讨了在孵化温度在诱导睾丸生产或卵巢生产之间波动的生态相关条件下性别决定是如何发生的。项目将侧重于对温度反应的时间方面，因为已经确定，特定孵化温度的暴露本质上是短暂的，个别胚胎的性腺命运是否受到短暂暴露（例如热浪）的影响是不同的。此外，项目将调查母体雌激素是否会影响诱导卵巢发育所需的暴露时间。通过描述参与性腺分化的基因表达如何对孵育温度的短暂暴露做出反应，以及雌激素如何影响这种反应，研究将开始解开分子对温暖和凉爽温度的反应如何独立变化。了解生物体对温度变化的反应将加强我们对环境温度如何调节生物过程（如性别决定）的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Most organisms respond to environmental temperatures, and these responses are typically studied by comparing individuals held at one temperature to individuals held at a different temperature. This approach misses two important points: 1) temperatures in nature are often variable and exposure to a given temperature can be transient, and 2) it does a poor job quantifying variation in how long it takes individuals to respond to temperature. This project focuses on understanding why some individuals respond to a short exposure to a given temperature, while others do not. Studies will be conducted using the red-eared slider turtle (Trachemys scripta), where incubation temperatures affect sex determination, which provides a clear signal (i.e., formation of a testis or ovary) of how individuals responded to temperature. Specifically, cool incubation temperatures induce testis development and warm incubation temperatures induce ovary development. It is also established that higher levels of estrogens in the egg increase the likelihood that the embryos will develop ovaries. Under natural conditions, embryos routinely experience both testis and ovary inducing temperatures, so studies are aimed at deciphering how long of an exposure to warmer temperatures is necessary to induce ovary development and whether elevated estrogen levels reduce the exposure requirement. Advancing our understanding of how temperature affects sex determination will assist efforts to mitigate the effect of climate change on thermally sensitive species. The project will train a postdoctoral researcher, graduate and undergraduate students, and will engage pre-college students in STEM-related activities. Recent studies have demonstrated that temperature-dependent sex determination involves epigenetic regulation of critical transcription factors that determine sex. In the red-eared slider turtle (Trachemys scripta), the histone demethylase Kdm6b removes repressive histones marks from the promoter of Dmrt1, which is a conserved regulator of testis development. For this species, testis development is induced at cool incubation temperatures (below 29˚C). This proposal examines how sex determination occurs under ecologically relevant conditions where incubation temperatures fluctuate between those that induce either testis production or ovary production. Projects will focus on the temporal aspect of the response to temperatures since it is established that exposure to specific incubation temperatures is transient in nature and individual embryos vary in whether their gonadal fate is influenced by brief exposures (e.g., heatwaves). Additionally, projects will investigate whether maternal estrogens affect the duration of exposure necessary to induce ovarian development. By characterizing how the expression of genes involved in gonadal differentiation respond to transient exposure to incubation temperature and how estrogens my influence that response, studies will begin to disentangle how molecular responses to warm and cool temperature may vary independently. Understanding how an organism responds to thermal variation will strengthen our understanding of how environmental temperatures regulate biological processes such as sex determination.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.