This application is a direct continuation of our previous grant directed at the genetic mapping of QTL controlling macronutrient selection in the C67BL/6J and CAST/Ei mouse inbred strains which differ markedly in their self-selected intake of macronutrient diets. A genome-wide scan revealed significant linkage for traits representing self-selected fat and carbohydrate intake on chromosome 6, 8, 17, 18 and X. Loci on chromosome 17 and 18 were linked also to total energy intake when body weight was used as a covariate. These are the first QTL for food preference or total energy intake that have been mapped in the mouse. The overall goal of the current proposal is to identify candidate genes underlying Mnif1, a quantitative trait locus (QTL) for dietary fat intake located on chromosome 8, and Mnic1 on chromosome 17 for carbohydrate and kilocalorie intake.
In Aim 1, we will isolate and narrow the Mnif1 and Mnic1 intervals to a size suitable for the positional candidate approach, by developing B6.CAST congenic and subcongenic lines.
In Aim 2, gene expression microarrays will be used to identify candidate genes. The probes for the microarrays will consist of cDNA from tissues of the recipient strain (B6) and the interval-specific subcongenic strains (B6.CAST) developed in our laboratory, mRNA will be harvested from tissues important in the regulation of food intake phenotypes, i.e, hypothalamus, solitary tract nucleus/area postrema, liver, stomach, small intestine, pancreas, adipocyte, muscle. First, a genome-wide gene expression screen will be performed using a mouse oligonucleotide array (16,463 genes from UniGene) now ready and available from the PBRC Genomics Core. Thus we will characterize transcriptional differences that occur upstream or downstream from effects of genes within the QTL. These data will provide an entry point for modelling the process by which these feeding behaviors are controlled, and for identifying the most promising tissues to profile with the QTL-specific arrays. Next, custom arrays will be designed for the purpose of performing comprehensive analyses of the transcriptional activity of all mouse and human genes present in the subcongenic intervals for the QTL controlling fat intake on Chr 8 (Mnif1) and carbohydrate intake on Chr 17 (Mnic1). Knowledge of the biology of the feeding traits and analysis of differentially expressed genes within and outside of the QTL will help us reduce the number of candidates to a very few and select those that deserve further investigation for a functional role in determining the phenotype. Candidate gene identification will enhance our understanding of the regulation of food intake. Finding genes regulating macronutrient intake in mice will help us to understand the contribution of genetic versus environmental factors affecting food preferences in humans. This should lead to valuable insights into obesity and diabetes, and new approaches for modifying macronutrient selection that could be useful in controlling weight gain or promoting weight loss.
