Abstract：
Bullfrog (Rana catesbeiana) larvae inhabiting the main island of Japan overwinter as preclimax animals, whereas the larvae that reached climax in summer complete metamorphosis. We analyzed the mRNA expression levels of the adenohypophyseal hormones, hypothalamic hormones, and their receptors that are involved in controlling metamorphosis in tadpoles at various developmental stages available in summer and winter in order to understand the hormonal mechanism regulating metamorphosis progression. Corticotropin-releasing factor (CRF) and thyrotropin β-subunit (TSHβ) mRNA expression was enhanced as they reached the climax stage in metamorphosing summer tadpoles, although type 2 CRF receptor (CRFR2) mRNA levels demonstrated a tendency of elevation, indicating the activation of the hypothalamo-hypophyseal axis for stimulating the release of thyroid hormone in summer. Arginine vasotocin (AVT) mRNA levels were elevated as metamorphosis progressed, but mRNA expression levels were not synchronized with those of proopiomelanocortin (POMC) and V1b-type AVT receptor (V1bR). The elevation of mRNA levels of prolactin (PRL) 1A and type 3 thyrotropin-releasing hormone receptor (TRHR3), but not of thyrotropin-releasing hormone (TRH) precursor mRNA levels, was noted in climactic tadpoles, indicating that PRL mRNA levels are not simply dependent on the expression levels of TRH precursor mRNA. In the preclimactic larvae captured in winter, which are in metamorphic stasis, mRNA levels of pituitary hormones, hypothalamic factors, and their receptors remained low or at levels similar to those of the larvae captured in summer. These results indicate the relationship between the mRNA expression of metamorphosis-related factors and the seasonal progression/stasis of metamorphosis.
摘要：
居住在日本主岛的牛蛙（Ranacatesbeiana）幼虫越冬，而在夏季达到高潮的幼虫则完全变态。我们分析了腺垂体激素的mRNA表达水平，下丘脑激素,以及它们的受体，这些受体在夏季和冬季可用的各个发育阶段都参与控制t的变态，以了解调节变态进程的激素机制。促肾上腺皮质激素释放因子（CRF）和促甲状腺激素β亚基（TSHβ）mRNA的表达在变态夏季t中达到高潮阶段时得到增强，尽管2型CRF受体（CRFR2）mRNA水平显示出升高的趋势，指示下丘脑-垂体轴的激活，以刺激夏季甲状腺激素的释放。精氨酸血管生成素（AVT）mRNA水平随着变态的发展而升高，但mRNA表达水平与前黑皮质素（POMC）和V1b型AVT受体（V1bR）的表达水平不同步。催乳素（PRL）1A和3型促甲状腺激素释放激素受体（TRHR3）的mRNA水平升高，但不是促甲状腺激素释放激素（TRH）前体mRNA水平，在高潮的t中被注意到，表明PRLmRNA水平并不简单依赖于TRH前体mRNA的表达水平。在冬季捕获的前陆生幼虫中，处于变质停滞状态，垂体激素的mRNA水平，下丘脑因素，它们的受体保持在较低水平或与夏季捕获的幼虫相似的水平。这些结果表明变态相关因子的mRNA表达与变态的季节性进展/停滞之间的关系。
