Dissertation Research: Evaluating the role of thyroid hormone in embryonic limb development in direct-developing frogs

这项研究将阐明甲状腺激素在两栖动物肢体发育中的作用。荷尔蒙是体内产生的物质，会影响身体的生长发育方式。甲状腺激素在蝌蚪向青蛙的转变过程中起着重要作用，特别是在肢体发育过程中。近三分之一的青蛙物种绕过蝌蚪阶段，直接发育成青蛙，甲状腺激素在这些物种发育过程中的作用尚不清楚。这个项目将测试两种关于甲状腺激素在这一过程中的作用的替代假设。该项目还将与哈佛自然历史博物馆合作，为K-12年级的学生、教师和家长开展几项关于两栖动物生物多样性的教育活动。其中一些活动可以以很低的成本提供，这将让许多学生体验野生动物，并亲眼目睹自己变态的戏剧性变化。比较直接发育和变态青蛙肢体发育过程中甲状腺激素对基因活动的调节，可以告诉我们基本的内分泌网络是如何进化和产生不同的生命周期的。双相青蛙(经历变态)需要甲状腺激素(TH)来进行变态和肢体发育。本研究评估了TH在直接发育蛙类Eleutherodactylus coqui的肢体发育中的作用，以比较其在三个双相蛙类(非洲爪蛙、Bombina orientalis和Dendrobates tinctorius)中的作用。下一代测序将用于表征和比较TH诱导的所有四个物种发育肢体的分子表型。这项研究将为进一步研究两栖动物的生活史进化提供基础，并识别变态过程中高度保守的分子机制的种间变异。刻画一个种群如何实现直接发展，将为研究其他两栖动物生命历史的重复起源提供比较，并解决内分泌学、进化和发育的交叉点问题。

This study will clarify the role of thyroid hormone in the development of amphibian limbs. Hormones are substances produced in the body that influences the way the body grows or develops. Thyroid hormone plays an important role in the transition of tadpoles into frogs, especially in limb development. Nearly a third of frog species bypass the tadpole stage and develop directly into frogs and the role of thyroid hormone in the development of these species is not known. This project will test two alternative hypotheses about the role of thyroid hormone in this process. In association with the Harvard Museum of Natural History, this project will also develop several educational activities on amphibian biodiversity for K-12 students, teachers, and parents. Some of these activities can be offered at little cost, which will allow many students to experience wildlife and witness the dramatic transformation of metamorphosis for themselves.Comparing how thyroid hormone regulates gene activity during limb development between direct-developing and metamorphosing frogs can tell us how fundamental endocrine networks evolve and generate different life cycles. Biphasic frogs (which undergo metamorphosis) require thyroid hormone (TH) for metamorphosis and limb development. This study evaluates the role of TH in limb development in the direct-developing frog Eleutherodactylus coqui for comparison to its role in three biphasic frog taxa (Xenopus laevis, Bombina orientalis, and Dendrobates tinctorius). Next-generation sequencing will be used to characterize and compare the TH-induced molecular phenotype in the developing limb of all four species. This study will provide a basis for further studies of amphibian life history evolution and identify interspecific variation in an otherwise highly conserved molecular mechanism of metamorphosis. Characterizing how one group achieves direct development will provide a comparison for investigating the repeated origins of this life history in other amphibians, and address questions at the intersection of endocrinology, evolution, and development.