Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Department of Genetics, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Proc Natl Acad Sci U S A. 2019 May 14;116(20):9893-9902. doi: 10.1073/pnas.1900343116. Epub 2019 Apr 24.
The ecdysone pathway was among the first experimental systems employed to study the impact of steroid hormones on the genome. In and other insects, ecdysone coordinates developmental transitions, including wholesale transformation of the larva into the adult during metamorphosis. Like other hormones, ecdysone controls gene expression through a nuclear receptor, which functions as a ligand-dependent transcription factor. Although it is clear that ecdysone elicits distinct transcriptional responses within its different target tissues, the role of its receptor, EcR, in regulating target gene expression is incompletely understood. In particular, EcR initiates a cascade of transcription factor expression in response to ecdysone, making it unclear which ecdysone-responsive genes are direct EcR targets. Here, we use the larval-to-prepupal transition of developing wings to examine the role of EcR in gene regulation. Genome-wide DNA binding profiles reveal that EcR exhibits widespread binding across the genome, including at many canonical ecdysone response genes. However, the majority of its binding sites reside at genes with wing-specific functions. We also find that EcR binding is temporally dynamic, with thousands of binding sites changing over time. RNA-seq reveals that EcR acts as both a temporal gate to block precocious entry to the next developmental stage as well as a temporal trigger to promote the subsequent program. Finally, transgenic reporter analysis indicates that EcR regulates not only temporal changes in target enhancer activity but also spatial patterns. Together, these studies define EcR as a multipurpose, direct regulator of gene expression, greatly expanding its role in coordinating developmental transitions.
蜕皮激素途径是最早用于研究类固醇激素对基因组影响的实验系统之一。在 和其他昆虫中，蜕皮激素协调发育转变，包括幼虫在变态过程中整体转化为成虫。像其他激素一样，蜕皮激素通过核受体控制基因表达，核受体作为配体依赖性转录因子发挥作用。尽管很明显蜕皮激素在其不同的靶组织中引发了不同的转录反应，但它的受体 EcR 在调节靶基因表达中的作用还不完全清楚。特别是，EcR 响应蜕皮激素启动转录因子表达的级联反应，这使得不清楚哪些蜕皮激素反应基因是直接的 EcR 靶基因。在这里，我们使用发育中的翅膀从幼虫到预蛹的转变来研究 EcR 在基因调控中的作用。全基因组 DNA 结合谱揭示 EcR 在基因组中广泛结合，包括许多典型的蜕皮激素反应基因。然而，它的大多数结合位点位于具有翅膀特异性功能的基因上。我们还发现 EcR 结合具有时间动态性，数千个结合位点随时间变化。RNA-seq 表明 EcR 既作为阻止过早进入下一个发育阶段的时间门控，也作为促进随后程序的时间触发。最后，转基因报告基因分析表明 EcR 不仅调节靶增强子活性的时间变化，还调节空间模式。总之，这些研究将 EcR 定义为基因表达的多用途直接调节因子，极大地扩展了其在协调发育转变中的作用。
