Proopiomelanocortin Gene Expression and Obesity

 描述(申请人提供)：肥胖使人类易患糖尿病和心血管疾病，是对健康的普遍威胁。脂肪储存是由大脑和外周之间协调的激素、神经和代谢信号动态控制的。合成黑素皮质素多肽的前阿片黑素皮质素(POMC)神经元是这些与能量平衡相关的不同信号的主要整合部位。在过去的资金周期中，我们在解释POMC转录如何限于下丘脑神经元子集方面取得了重大进展。由两个进化上不同的增强子组成的模块化基因座指导神经元特异性POMC的表达。靶向缺失单个nPE1、nPE2或结合元件表明，它们在下丘脑发育期间协同作用，并在成年生活中额外地保持足够强大的POMC转录，以避免肥胖。对增强子内核心核苷酸序列基序的生物信息学分析，结合对动物模型中候选同源结构域转录因子(TF)的解剖和功能询问，发现Isl1和Nkx2.1在指导弓状核中POMC表达的独特时空模式方面做出了主要贡献。虽然这两个因素是必要的，但仅有这两个因素不足以完全解释神经元POMC调控的复杂性。因此，我们提出了这个项目更新的以下具体目标：1)通过利用互补的小鼠和斑马鱼分子遗传学对控制胚胎发育、识别和维持POMC神经元表型的整套转录因子进行功能鉴定，破译控制下丘脑POMC表达的转录密码；2)鉴定控制下丘脑POMC表达的神经元增强子中的整套顺式作用调控元件，并研究它们之间的相互作用，以组装一个完整功能的转录位点；以及3)剖析nPE1、nPE2及其同源转录因子对POMC表达和代谢调节的生理作用，与瘦素信号和妊娠和哺乳的能量需求相关。这些研究将提供对调节体重至关重要的基因的基础知识，并可能识别可用于治疗目的的新的遗传或信号通路。

 DESCRIPTION (provided by applicant): Obesity predisposes humans to diabetes and cardiovascular disease and is a universal threat to health. Fat storage is dynamically controlled by orchestrated hormonal, neural and metabolic signals between brain and periphery. Proopiomelanocortin (POMC) neurons that synthesize melanocortin peptides are a primary integrative site for these diverse signals related to energy homeostasis. In the past funding cycles, we made significant progress towards explaining how Pomc transcription is restricted to a subset of hypothalamic neurons. A modular locus comprised of two evolutionarily distinct enhancers directs neuron-specific Pomc expression. Targeted deletion of the individual nPE1, nPE2 or combined elements revealed that they act synergistically during hypothalamic development and additively in adult life to maintain sufficiently robust Pomc transcription to avoid obesity. A bioinformatic analysis of core nucleotide sequence motifs within the enhancers combined with anatomic and functional interrogation of candidate homeodomain transcription factors (TFs) in animal models identified a major contribution of Isl1 and Nkx2.1 in directing the unique temporal and spatial patterns of Pomc expression in the arcuate nucleus. Although necessary, these two factors alone are not sufficient to fully account for the complexities of neuronal Pomc regulation. Therefore, we propose the following specific aims for this project renewal: 1) Decipher the transcriptional code that controls hypothalamic Pomc expression through the functional identification of the entire set of TFs that control the embryonic development, identity and maintenance of the POMC neuronal phenotype using complementary mouse and zebrafish molecular genetics; 2) Identify the entire set of cis-acting regulatory elements in the neuronal enhancers that control hypothalamic Pomc expression and investigate their interactions to assemble a fully functional transcriptional locus; and 3) Dissect the physiological roles of nPE1, nPE2, and their cognate TFs on Pomc expression and metabolic regulation associated with leptin signaling and the energy demands of pregnancy and lactation. These studies will provide fundamental knowledge about a gene essential for regulating body mass and possibly identify novel genetic or signaling pathways that can be exploited for therapeutic purposes.