Evolution of Endocrine Control in Direct-Developing Amphibians

小行星9321572 该提案概述了一系列描述性和实验性研究，检查激素介导的胚胎发育直接发展无尾两栖类。甲状腺轴的早熟活动经常被认为是直接发育的机制，但这从未得到充分的研究。为了验证这一假设，在一个直接发展的青蛙甲状腺轴的最初外观和随后的发展将比较观察到的模式在变态青蛙。甲状腺激素（TH）在介导直接发育中的作用也将通过操纵内源性激素水平进行实验评估。 方法包括组织学（记录甲状腺和正中隆起形成），放射免疫测定（通过胚胎发育确定TH水平），免疫细胞化学（检查促甲状腺细胞的个体发育和TH受体表达），和激素操作（实验检查TH在直接发育中的作用）。分析将集中在胚胎的直接发育青蛙Eleutherodactylus coqui（Leptodactylidae）来自一个既定的繁殖群体。 为了比较的目的，分析还将包括几个变态物种，包括白唇细趾虎（Leptodactylidae），东方铃蟾（Discoglossidae）和非洲爪蟾（Pipidae）。 研究结果将有助于我们了解两栖动物直接发育的内分泌调节。它们还将提供关于生命史进化的机械基础的新信息。此外，这项研究将探讨母体提供的激素在早期胚胎发生和发展，相关的过程，以了解在所有类别的脊椎动物的早期发展。 ***

9321572 Hanken This proposal outlines a series of descriptive and experimental studies that examine the hormonal mediation of embryonic development in direct-developing anurans. Precocious activity of the thyroid axis is frequently cited as the mechanism underlying direct development, but this has never been fully examined. To test this hypothesis, initial appearance and subsequent development of the thyroid axis in a direct-developing frog will be compared to the patterns observed in metamorphosing frogs. The role of thyroid hormones (TH) in mediating direct development will also be evaluated experimentally by manipulating endogenous hormone levels. Methods include histology (to document thyroid gland and median eminence formation), radioimmunoassay (to determine TH levels through embryonic development), immunocytochemistry (to examine the ontogeny of thyrotropic cells and TH receptor expression), and hormone manipulation (to experimentally examine the roles of TH in direct development). Analyses will focus on embryos of the direct developing frog Eleutherodactylus coqui (Leptodactylidae) derived from an established breeding colony. For comparative purposes, analyses will also include several metamorphosing species, including Leptodactylus albilabris (Leptodactylidae), Bombina orientalis (Discoglossidae), and Xenopus laevis (Pipidae). Results will contribute to our understanding of the endocrine mediation of direct development in amphibians. They also will provide new information on the mechanistic basis underlying life-history evolution. In addition, this study will examine maternal provisioning of hormones in early embryogenesis and development, a process relevant to understanding early development in all classes of vertebrates. ***