Mechanisms of glucosensation mediating food choice behavior in Drosophila

描述(申请人提供)：部分由于全球肥胖症和糖尿病发病率的上升，调节摄食行为的分子机制受到了极大的关注。然而，尽管我们对食物摄取和新陈代谢如何协调的了解有了极大的提高，但对食物背后的神经回路和基因知之甚少。此外，新陈代谢(补充能量)和享乐(奖励)喂养回路的信号如何整合以调节食物摄入量和食物选择仍不清楚。虽然已经从哺乳动物模型生物中学到了很多东西，但由于在这些模型中进行遗传筛选的困难，涉及摄食行为和能量动态平衡的基因很少。因此，使用一种遗传上可服从的模式生物，如果蝇，为补充哺乳动物的研究提供了一个理想的策略。在我的博士后研究期间，我开发了一种方法来研究果蝇的食物选择行为，并发现果蝇配备了一种机制，可以独立于味道来检测食物的营养价值。具体地说，缺乏食物的果蝇更喜欢高卡路里的糖，而不是零卡路里的甜味剂。通过遗传和行为筛选，我确定了一种保守基因，这是苍蝇做出新陈代谢摄食选择所必需的。该基因是果蝇钠-葡萄糖转运蛋白(DSGLT)的候选基因，在果蝇脑中的一小部分神经元中表达。我的假设是，dSGLT通过监测血液中的葡萄糖水平来调节食物选择。事实上，在哺乳动物下丘脑中表达的该基因的同源基因被认为通过影响神经元的兴奋性在应对血糖水平变化方面发挥积极作用，但它们在进食中的作用尚不清楚。由于下丘脑对葡萄糖的神经感觉缺陷已被证明在肥胖的发生和2型糖尿病的发生中起作用，因此更好地了解摄食和代谢中葡萄糖感觉的分子机制是至关重要的。在这项建议中，我提出了一个有针对性的策略来表征果蝇候选基因dSGLT在葡萄糖感觉和行为中的功能。我将确定dSGLT是否是葡萄糖感受器，以及它如何将葡萄糖感受性赋予表达它的神经元。我会分析表达这个基因的神经回路是否有必要 足够选择可代谢的糖，以及这些神经元中葡萄糖感觉的动态如何调节食物选择行为。最后，我将进行两个有针对性的遗传筛选：一个是确定dSGLT神经元中葡萄糖感应下游涉及的其他基因，另一个是确定SGLT神经元下游的神经肽和神经肽回路，这些神经肽和神经肽回路介导最终调节食物选择的效应机制。这些研究将为深入了解葡萄糖敏感的分子机制及其在摄食中的作用提供依据。它们还将为哺乳动物研究人员提供保守的基因，在未来的葡萄糖敏感、摄食和疾病研究中用作分子和神经化学标记。

DESCRIPTION (provided by applicant): Due in part to the rise in the worldwide incidence of obesity and diabetes, the molecular mechanisms regulating feeding behavior have received much attention. However, despite the tremendous increases in our understanding of how food intake and metabolism are coordinated, very little is known about the neural circuits and genes underlying feeding. Furthermore, how signals from both metabolic (to replenish energy) and hedonic (for reward) feeding circuits are integrated to regulate food intake and food choice remain unclear. While much has been learned from mammalian model organisms, very few genes involved in feeding behavior and energy homeostasis have been identified because of the difficulty in performing genetic screens in these models. Thus, using a genetically amenable model organism such as the fruit fly provides an ideal strategy to complement mammalian research. During my postdoctoral studies I developed an assay to study food choice behavior in Drosophila and found that flies are equipped with a mechanism to detect the nutritional value of food independently of taste. Specifically, food-deprived flies prefer calorie-rich sugars to zero-calorie sweeteners. Through genetic and behavioral screens, I identified a conserved gene that is required for flies to make metabolic feeding choices. This gene, a candidate Drosophila Sodium-Glucose-Transporter (dSGLT) is expressed in a small subset neurons in the fly brain. My hypothesis is that dSGLT regulates food choice by monitoring glucose levels in the blood. Indeed, homologues of this gene expressed in the mammalian hypothalamus are thought to play an active role in responding to changing glucose levels by affecting the excitability of neurons, but their role in feeding is not known. As defects in neural sensing of glucose in the hypothalamus have been shown to play a role in the development of obesity and contribute to type-2 diabetes, it is of the utmost importance to better understand the molecular mechanism of glucosensation underlying feeding and metabolism. In this proposal I present a focused strategy to characterize the function of the fly candidate dSGLT in glucose-sensation and behavior. I will determine if dSGLT is a glucose sensor and how it confers glucosensing properties to the neurons that express it. I will analyze if the neural circuit expressing this gene is necessary and sufficient for the choice for metabolizable sugars, and how the dynamics of glucosensation in these neurons modulate food choice behavior. Finally, I will conduct two targeted genetic screens: one to identify other genes involved downstream of glucosensing in dSGLT neurons and the other to identify the neuropeptides and neuropeptide circuits downstream of SGLT neurons that mediate the effector mechanisms ultimately regulating food choice. These studies will provide insights into the molecular mechanisms of glucosensation and its role in feeding. They will also provide mammalian researchers with conserved genes to use as molecular and neurochemical markers in future studies of glucosensation, feeding, and disease.