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

本研究将阐明甲状腺激素在两栖动物肢体发育中的作用。激素是体内产生的影响身体生长或发育方式的物质。甲状腺激素在蝌蚪向青蛙的转变过程中起着重要的作用，尤其是在肢体发育过程中。近三分之一的蛙类绕过蝌蚪阶段直接发育为蛙类，甲状腺激素在这些蛙类发育中的作用尚不清楚。该项目将测试关于甲状腺激素在这一过程中作用的两种假设。该项目还将与哈佛自然历史博物馆合作，为K-12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。其中一些活动可以提供很少的费用，这将使许多学生体验野生动物，亲眼目睹自己的蜕变。比较甲状腺激素如何调节直接发育和变形蛙肢体发育过程中的基因活动，可以告诉我们基本的内分泌网络如何进化并产生不同的生命周期。双相蛙（经历变态）需要甲状腺激素（TH）来变态和肢体发育。本研究评估了TH在直接发育的coqui棘爪蛙（Eleutherodactylus coqui）肢体发育中的作用，并比较了其在三个双相蛙类群（非洲爪蟾、东方bomina orientalis和tinctorius dendroates）中的作用。下一代测序将用于表征和比较所有四个物种发育肢体中th诱导的分子表型。该研究将为进一步研究两栖动物的生活史进化和鉴定高度保守的变态分子机制中的种间变异提供基础。描述一个群体是如何实现直接发育的，将为研究其他两栖动物这一生活史的重复起源提供一个比较，并解决内分泌学、进化和发育交叉的问题。

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.