Regulation and Function of Drosophila Nuclear Receptors

描述（由申请人提供）：果蝇（Drosophila melanogaster）有18个核受体（NR）基因，明显少于人类中发现的48个基因，涵盖所有脊椎动物NR亚类，并编码关键人类受体的直系同源物，包括RXR（果蝇中的USP）、NGFI-B/NXR（DHR 38）、ERR（dERR）、SXR（DHR 96）和HNF 4（dHNF 4）。果蝇NR的这些特征，结合广泛收集的遗传和基因组工具，建立了果蝇作为研究NR调控和功能的分子机制的理想模型系统。在这个建议中，我们专注于2个主要的NR调节的生物学途径：类固醇触发的成熟和脂质代谢。像脊椎动物一样，果蝇的成熟是由类固醇激素及其受体通过在果蝇中鉴定和表征的复杂转录级联触发的。相比之下，迄今为止还没有研究涉及果蝇核受体在脂质代谢中的作用。我们将研究类固醇调节的一个知之甚少的过渡，发生在最后的幼虫阶段，当动物致力于终止其少年生长阶段，并通过变态开始成熟。我们将确定由α-蜕皮激素（E，果蝇中主要分泌的类固醇和活性激素20-羟基蜕皮激素或20 E的前体）调节的基因，并询问这些作用是否通过DHR 38 E受体及其RXR伴侣USP。我们将确定DHR 38和EcR是否作为部分冗余类固醇受体启动成熟。我们将确定是否dERR是转录控制的20 E，研究其可能的作用，在启动变态，并确定它是否控制脂质或固醇代谢。我们将跟踪观察到DHR 96与胆固醇共纯化，并且DHR 96无效突变体需要胆固醇才能在基本培养基上存活。最后，我们将描述dHNF 4的表达和功能，以确定其在脂质代谢和发育中的作用。代谢分析和微阵列将用于获得更完整的了解dERR，DHR 96和dHNF 4功能的分子机制。选定的基因将被定义为直接的调控目标。这些研究将扩大我们对NR信号通路的理解，直接影响到人类中的orthogonal NR功能，以及它们对与NR功能障碍相关的关键人类疾病的贡献，包括心血管疾病，糖尿病和肥胖症。

DESCRIPTION (provided by applicant): The fruit fly Drosophila melanogaster has 18 nuclear receptor (NR) genes, significantly fewer than the 48 genes found in humans, spanning all vertebrate NR subclasses and encoding orthologs of key human receptors, including RXR (USP in flies), NGFI-B/NURR (DHR38), ERR (dERR), SXR (DHR96), and HNF4 (dHNF4). These characteristics of Drosophila NRs, combined with an extensive collection of genetic and genomic tools, establish the fly as an ideal model system for studying the molecular mechanisms of NR regulation and function. In this proposal, we focus on 2 major NR-regulated biological pathways: steroid-triggered maturation and lipid metabolism. Like vertebrates, Drosophila maturation is triggered by steroid hormones and their receptors, via complex transcriptional cascades that were identified and characterized in the fly. In contrast, no studies to date have addressed roles for Drosophila NRs in lipid metabolism. We will study the steroid regulation of a poorly understood transition that occurs during the last larval stage, when the animal commits to terminating its juvenile growth phase and initiating maturation via metamorphosis. We will identify genes regulated by alpha-ecdysone (E, the primary secreted steroid in Drosophila and the precursor to the active hormone 20-hydroxyecdysone, or 20E) and ask if these effects go through the DHR38 E receptor and its RXR partner, USP. We will determine if DHR38 and EcR function as partially redundant steroid receptors to initiate maturation. We will determine if dERR is transcriptionally controlled by 20E, examine its possible roles in initiating metamorphosis, and determine whether it controls lipid or sterol metabolism. We will follow up on the observation that DHR96 co-purifies with cholesterol and that DHR96 null mutants require cholesterol for their survival on minimal medium. Finally, we will characterize the expression and function of dHNF4 to define its roles in lipid metabolism and development. Metabolic profiling and microarrays will be used to gain a more complete understanding of the molecular mechanisms of dERR, DHR96, and dHNF4 function. Selected genes will be defined as direct regulatory targets. These studies will expand our understanding of NR signaling pathways with direct implications for how the orthologous NRs function in humans, as well as their contributions to critical human diseases associated with NR dysfunction, including cardiovascular disease, diabetes, and obesity.