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

大多数生物体对环境温度做出反应，通常通过比较处于同一温度下的个体和处于不同温度下的个体来研究这些反应。这种方法忽略了两个要点：1)自然界的温度通常是可变的，暴露在给定温度下可能是瞬时的；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。这个项目的重点是了解为什么一些人会对短时间暴露在给定温度下做出反应，而另一些人则不会。研究将使用红耳滑龟(Trachemys Scripta)进行，孵化温度会影响性别决定，这为个体对温度的反应提供了明确的信号(即睾丸或卵巢的形成)。具体地说，冷孵化温度诱导睾丸发育，温孵化温度诱导卵巢发育。研究还证实，卵子中雌激素水平较高会增加胚胎发育卵巢的可能性。在自然条件下，胚胎通常会同时经历睾丸和卵巢的诱导温度，因此研究的目的是破译在更温暖的温度下暴露多长时间才能诱导卵巢发育，以及提高雌激素水平是否会降低暴露要求。提高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温度敏感物种的影响。该项目将培养一名博士后研究员、研究生和本科生，并将吸引大学预科学生参加与STEM相关的活动。最近的研究表明，温度相关的性别决定涉及决定性别的关键转录因子的表观遗传调节。在红耳滑龟(Trachemys Scripta)中，组蛋白去甲基酶KDM6B去除了DMRT1启动子上的抑制性组蛋白标记，DMRT1是一种保守的睾丸发育调节因子。对于该物种，睾丸发育是在较冷的孵化温度(低于29˚C)下诱导的。这项建议研究了性别决定是如何在生态相关的条件下发生的，在这些条件下，孵化温度在诱导睾丸产生或卵巢产生的温度之间波动。项目将侧重于对温度的反应的时间方面，因为已经确定，暴露在特定孵化温度下本质上是瞬时的，每个胚胎的性腺命运是否受到短暂暴露(例如热浪)的影响而有所不同。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。通过表征参与性腺分化的基因的表达如何对短暂的孵化温度做出反应，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寒冷温度的反应可能是如何独立变化的。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。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.