Paul Bindu Diana, Fu Liezhen, Buchholz Daniel R, Shi Yun-Bo
Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Mol Cell Biol. 2005 Jul;25(13):5712-24. doi: 10.1128/MCB.25.13.5712-5724.2005.
Thyroid hormone receptors (TRs) can repress or activate target genes depending on the absence or presence of thyroid hormone (T3), respectively. This hormone-dependent gene regulation is mediated by recruitment of co-repressors in the absence of T3 and coactivators in its presence. Many TR-interacting coactivators have been characterized in vitro. In comparison, few studies have addressed the developmental roles of these cofactors in vivo. We have investigated the role of coactivators in transcriptional activation by TR during postembryonic tissue remodeling by using amphibian metamorphosis as a model system. We have previously shown that steroid receptor coactivator 3 (SRC3) is expressed and upregulated during metamorphosis, suggesting a role in gene regulation by liganded TR. Here, we have generated transgenic tadpoles expressing a dominant negative form of SRC3 (F-dnSRC3). The transgenic tadpoles exhibited normal growth and development throughout embryogenesis and premetamorphic stages. However, transgenic expression of F-dnSRC3 inhibits essentially all aspects of T3-induced metamorphosis, as well as natural metamorphosis, leading to delayed or arrested metamorphosis or the formation of tailed frogs. Molecular analysis revealed that F-dnSRC3 functioned by blocking the recruitment of endogenous coactivators to T3 target genes without affecting corepressor release, thereby preventing the T3-dependent gene regulation program responsible for tissue transformations during metamorphosis. Our studies thus demonstrate that coactivator recruitment, aside from corepressor release, is required for T3 function in development and further provide the first example where a specific coactivator-dependent gene regulation pathway by a nuclear receptor has been shown to underlie specific developmental events.
甲状腺激素受体（TRs）可分别根据甲状腺激素（T3）的缺失或存在来抑制或激活靶基因。这种激素依赖性基因调控分别由在无T3时募集共抑制因子和在有T3时募集共激活因子介导。许多与TR相互作用的共激活因子已在体外得到表征。相比之下，很少有研究探讨这些辅因子在体内的发育作用。我们以两栖类变态为模型系统，研究了共激活因子在胚胎后组织重塑过程中TR介导的转录激活中的作用。我们之前已表明，类固醇受体共激活因子3（SRC3）在变态过程中表达并上调，提示其在配体结合的TR介导的基因调控中发挥作用。在此，我们构建了表达显性负性形式SRC3（F-dnSRC3）的转基因蝌蚪。这些转基因蝌蚪在整个胚胎发育和变态前阶段表现出正常的生长和发育。然而，F-dnSRC3的转基因表达基本上抑制了T3诱导的变态以及自然变态的所有方面，导致变态延迟或停滞，或形成有尾蛙。分子分析表明，F-dnSRC3通过阻断内源性共激活因子向T3靶基因的募集发挥作用，而不影响共抑制因子的释放，从而阻止了负责变态过程中组织转化的T3依赖性基因调控程序。因此，我们的研究表明，除了共抑制因子的释放外，共激活因子的募集对于T3在发育中的功能也是必需的，并且进一步提供了第一个实例，证明核受体的特定共激活因子依赖性基因调控途径是特定发育事件的基础。
