Genetics of Macronutrient Selection and Energy Balance

描述(由申请人提供)：我们开发了一种独特的实验系统，以确定大量营养素选择和能量摄入的遗传决定因素，以及肥胖表型发展的基本饮食行为。此前，我们在C57BL/6J(B6)x CAST/EI(CAST)小鼠近交系中定位了控制脂肪、碳水化合物和总卡路里摄入量的复杂性状(数量性状基因座或QTL)的第一个遗传位点，分别选择了它们对脂肪和碳水化合物的偏好消费。接下来，我们开发了同源菌株，以获得连锁的独立证据，更准确地确定基因座，并帮助识别潜在的基因(S)。随后，在B6遗传背景上具有铸型供体片段的同源菌株已经确认了一个Chr 17 QTL，该QTL指定了两个原始的相关性状：MNic1(大量营养素摄入量-碳水化合物)和Kcal2(千卡摄入量)。具体地说，与同基因的B6对照相比，这种同源菌株每体重摄入的碳水化合物和总卡路里明显更多，但脂肪的量相似。重要的是，这种同源基因间隔也赋予了体力活动增加的表型。我们假设17号染色体上的QTL要么由(A)决定食物摄入量和自发体力活动的单基因位点编码，要么由(B)两个或多个基因编码，每个基因决定能量平衡的一个亚型。另一种假设是，行为性状的因果基因(S)位于Chr17同基因片段上的一个QTL上，该QTL与转录调控基因(Cis EQTL)共定位。因此，在目前的应用中，我们建议：1)通过对受体F2杂交的同源QTL进行精细结构遗传作图，解析控制营养摄入和身体活动表型的遗传区域；2)通过将同源F2基因与定制的低密度基因阵列相结合，确定精细定位的QTL中哪些基因表现出与行为表型(S)(即eQTL)分离的表达模式；3)根据从精细定位的QTL区域(S)中选择的候选基因的位置和转录调控(EQTL)，确定它们的序列、表达和功能。这项拟议研究的长期目标是确定在控制能量平衡方面调节食物摄入量和活动诱导的产热的分子机制。公共卫生相关性：这项研究项目已经确定了脂肪和碳水化合物的饮食偏好以及总卡路里摄入量的遗传联系。我们开发了一种新的动物模型来研究负责体力活动的遗传因素和控制食物摄入量的遗传因素之间的关系。发现与这些特征有关的基因，对于理解导致肥胖的饮食行为的潜在机制，以及控制能量平衡具有重要意义。

DESCRIPTION (provided by applicant): We have developed a unique experimental system to identify the genetic determinants of macronutrient selection and energy intake, eating behaviors fundamental to the development of obesity phenotypes. Previously we identified the first genetic loci in mouse controlling complex traits (quantitative trait loci or QTL) for fat, carbohydrate, and total calorie intake in mapping population C57BL/6J (B6) x CAST/Ei (CAST) mouse inbred strains, selected for their preferential consumption of fat or carbohydrate, respectively. Next we developed congenic strains to obtain independent evidence for linkage, to determine the locus more precisely, and to aid in identification of the underlying gene(s). Subsequently, a congenic strain possessing a CAST donor segment on the B6 genetic background has confirmed a Chr 17 QTL that specified two of the original, linked traits: Mnic1 (macronutrient intake-carbohydrate) and Kcal2 (kilocalorie intake). Specifically, this congenic strain eats significantly more carbohydrate and total calories per body weight, yet a similar amount of fat, compared with littermate B6 controls. Importantly, this congenic interval also confers a phenotype of increased physical activity. We hypothesize that the QTL on Chromosome 17 is either encoded by (a) a single gene locus that determines both food intake and spontaneous physical activity, or by (b) two or more genes, each determining a sub-phenotype of energy balance. A further hypothesis is that the causal gene(s) for the behavioral traits is located in a QTL within the Chr 17 congenic segment that co-localizes with transcriptionally regulated genes (cis eQTLs). Therefore in the current application, we propose: 1) To resolve the genetic regions responsible for nutrient intake and physical activity phenotypes in the Chr 17 QTL, through fine structure genetic mapping of known QTLs for nutrient intake in a congenic by recipient F2 cross, 2) To determine which genes within the fine mapped QTL exhibit expression patterns that segregate with the behavioral phenotype(s) (i.e., eQTL), by combining the congenic F2 genotypes with custom low density gene arrays, and 3) To characterize gene candidates selected from the fine mapped QTL region(s) based on their location and transcriptional regulation (eQTLs) by determining their sequence, expression and function. The long-term goal of the proposed studies is to identify the molecular mechanisms regulating food intake and activity-induced thermogenesis in the control of energy balance. Public Health Relevance: This research project has identified genetic links to dietary preferences for fat and carbohydrate, and to total calorie intake. We have developed a new animal model to study the relationship between the genetic factors responsible for physical activity and those controlling food intake. Discovering genes that are involved in these traits is of major importance toward understanding the mechanisms underlying eating behaviors that lead to obesity, and the control of energy balance.