Shi Y B, Wong J, Puzianowska-Kuznicka M, Stolow M A
Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, National Institute of Health, Bethesda, MD 20892, USA.
Bioessays. 1996 May;18(5):391-9. doi: 10.1002/bies.950180509.
Amphibian metamorphosis is a post-embryonic process that systematically transforms different tissues in a tadpole. Thyroid hormone plays a causative role in this complex process by inducing a cascade of gene regulation. While natural metamorphosis does not occur until endogenous thyroid hormone has been synthesized, tadpoles are competent to respond to exogenous thyroid hormone shortly after hatching. In addition, even though the metamorphic transitions of individual organs are all controlled by thyroid hormone, each occurs at distinct developmental stages. Recent molecular studies suggest that this competence of premetamorphic tadpoles to respond to the hormone and the developmental stage-dependent regulation of tissue-specific transformations are determined in part by the levels of thyroid hormone receptors and the concentrations of cellular free thyroid hormone. In addition, at least two genes, encoding a cytosolic thyroid hormone binding protein and a 5-deiodinase, respectively, are likely to be critical players in regulating cellular free thyroid hormone concentrations. This review discusses how all of these molecular components coordinate to induce amphibian metamorphosis in a correct spatial and temporal manner. These studies provide us with general clues as to how and why tissues become competent to respond to hormonal signals.
两栖动物变态是一个胚胎后过程，它系统性地转变蝌蚪体内的不同组织。甲状腺激素通过诱导一系列基因调控，在这个复杂过程中发挥着因果作用。虽然直到内源性甲状腺激素合成后自然变态才会发生，但蝌蚪在孵化后不久就有能力对外源甲状腺激素作出反应。此外，尽管各个器官的变态转变均由甲状腺激素控制，但每个转变都发生在不同的发育阶段。最近的分子研究表明，变态前蝌蚪对激素作出反应的这种能力以及组织特异性转变的发育阶段依赖性调控，部分是由甲状腺激素受体水平和细胞游离甲状腺激素浓度决定的。此外，至少有两个分别编码一种胞质甲状腺激素结合蛋白和一种5-脱碘酶的基因，可能是调节细胞游离甲状腺激素浓度的关键因素。这篇综述讨论了所有这些分子成分如何以正确的空间和时间方式协同作用以诱导两栖动物变态。这些研究为我们提供了关于组织如何以及为何有能力对激素信号作出反应的一般线索。
