Evolution of Endocrine Control in Direct-Developing Amphibians

9321572汉肯这项建议概述了一系列描述性和实验研究，考察了激素对直接发育的无尾两栖动物胚胎发育的调节作用。甲状腺轴的早熟活动经常被认为是直接发育的机制，但这一点从未得到充分的检验。为了验证这一假设，直接发育的青蛙的甲状腺轴的初始外观和随后的发育将与在变态青蛙中观察到的模式进行比较。甲状腺激素(TH)在调节直接发育中的作用也将通过控制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的形成)，放射免疫分析(通过胚胎发育来确定TH水平)，免疫细胞化学(检查促甲状腺细胞的个体发育和TH受体的表达)，以及激素操作(实验研究TH在直接发育中的作用)。分析将集中在直接发育的青蛙Eleutherodactylus coqui(Leptodactylidae)的胚胎上，这些青蛙来自一个已建立的繁殖群体。为便于比较，分析还将包括几个变态物种，包括白色细爪虾(细趾)、东方文昌鱼(盘舌科)和非洲爪蛙(非洲爪哇科)。这些结果将有助于我们理解内分泌调节两栖动物直接发育的机制。它们还将提供有关生命史进化的机制基础的新信息。此外，这项研究将研究早期胚胎发生和发育中母体激素的供应，这一过程与了解所有种类脊椎动物的早期发育有关。***

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. ***