Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, Michigan, USA.
Curr Top Dev Biol. 2013;103:195-227. doi: 10.1016/B978-0-12-385979-2.00007-1.
The timing of metamorphosis is a central amphibian life history trait and is controlled by the interplay of developmental progression, body size and condition, and environmental signals. These different processes and signals are integrated by the neuroendocrine system to regulate production of hormones by the thyroid gland. Thyroid hormone (TH) is the primary morphogen controlling metamorphosis, while corticosteroids (CSs) produced by the interrenal glands synergize with TH to promote metamorphic changes. The actions of TH are modulated by monodeiodinase enzymes expressed in TH target tissues. CSs act by sensitizing tissues to the actions of TH via the upregulation of TH receptors and monodeiodinases. The increase in thyroid gland activity during metamorphosis is controlled by the hypothalamus and pituitary gland. The hypothalamo-pituitary-thyroid and hypothalamo-pituitary-interrenal axes are regulated at multiple levels. Hypothalamic corticotropin-releasing factor (CRF) functions as a common, central regulator of pituitary thyroid-stimulating hormone (TSH) and adrenocorticotropic hormone (ACTH) secretion in tadpoles. CRF neurons transduce the signals of environmental change (e.g., pond drying, resource availability, etc.) on metamorphic timing by regulating TSH and ACTH secretion, and consequently the production of TH and CS.
变态的时间是一个中央两栖动物生活史的特征，是由发育进展、身体大小和条件以及环境信号的相互作用控制的。这些不同的过程和信号被神经内分泌系统整合，以调节甲状腺产生激素。甲状腺激素（TH）是控制变态的主要形态发生素，而由肾上腺分泌的皮质类固醇（CSs）与 TH 协同作用，促进变态变化。TH 的作用通过在 TH 靶组织中表达的单脱碘酶酶来调节。CSs 通过上调 TH 受体和单脱碘酶使组织对 TH 的作用敏感来发挥作用。变态过程中甲状腺活动的增加受下丘脑和垂体的控制。下丘脑-垂体-甲状腺和下丘脑-垂体-肾上腺轴在多个水平上受到调节。促肾上腺皮质激素释放因子（CRF）作为一种常见的中央调节剂，在蝌蚪中调节垂体促甲状腺激素（TSH）和促肾上腺皮质激素（ACTH）的分泌。CRF 神经元通过调节 TSH 和 ACTH 的分泌，以及 TH 和 CS 的产生，将环境变化（如池塘干涸、资源可用性等）的信号转化为变态时间的信号。
