Genomic Characterization of Two Models of Obesity in Mice: Divergent Selection for Epididymal Fat and the Effects of trans-10, cis-12-Conjugated Linoleic Acid

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Title: Genomic Characterization of Two Models of Obesity in Mice: Divergent Selection for Epididymal Fat and the Effects of trans-10, cis-12-Conjugated Linoleic Acid
Author: Ceddia, Ryan Patrick
Advisors: Melissa S. Ashwell, Committee Chair
Eugene J. Eisen, Committee Member
Christopher M. Ashwell, Committee Member
Jack Odle, Committee Member
Abstract: Obesity is rapidly becoming a major problem in the United States and throughout the world. Polygenic models of obesity are most similar to human obesity because few humans are genetically obese due to a mutation in a single gene. Numerous studies have selected mice for body size and growth rate as models for selection of agriculturally important species. One series of selection experiments produced lines of mice having differing epididymal fat (EF) masses but similar body weights. These mice may be used as a model for adipose deposition without confounding the effects of body weight. One method of studying these mice is to examine gene expression. Expression of thousands of genes can be investigated at one time using microarrays. We used microarrays and real-time RT-PCR to compare gene expression between the high epididymal (HE) and low fat (LF) lines of mice, which have dissimilar EF mass but similar body weights. Microarray analysis identified 19 genes with differential expression between the HE and LF lines of mice with 5 of these genes differentially expressed in both liver and EF tissues. We found differential regulation of genes known to play a role in glucose uptake and lipid metabolism. In addition, we identified a differentially expressed gene, solute carrier family 22 member 4, located within the confidence interval of a quantitative trait loci associated with EF mass, making it a positional candidate. Furthermore, we identified a linked group of three genes (Sortilin 1, guanine nucleotide binding protein alpha inhibiting 3, and selenium-binding protein 2) on Mus musculus chromosome 3 (MMU3), which may represent a genomic "hot spot" for genes associated with EF mass. In this study, differential expression of several genes not previously associated with obesity or adipose deposition were identified and may represent new targets for further research. Another aspect of obesity currently being investigated is anti-obesity compounds. One such compound is trans-10, cis-12-conjugated linoleic acid (CLA). CLA has been reported to reduce body weight and adipose mass in many species. Numerous studies have reported an increase in size, cytoplasmic vacuolization, and fatty acid synthesis in liver of CLA fed mice. The livers of CLA fed mice gain mass due to lipid accumulation; however, the precise molecular mechanisms are unknown. To elucidate these mechanisms, we examined the fatty acid composition, histology, and gene expression profile of liver from a polygenic obese line of mice fed CLA. Using a Periodic acid-Schiff stain, histological evidence suggests that glycogen content is unchanged in the liver of the CLA fed mouse implying that hepatic cytoplasmic vacuolization is due to increased lipid content. Microarray analysis identified 1393 genes differentially expressed at a nominal P-value of 0.01. Following Bonferroni correction and excluding lowly expressed transcripts, 198 genes were identified as being differentially expressed with 17 genes having ≥2 fold change. Real-time RT-PCR showed up regulation of acylglycerol-3-phosphate O-acyltransferase 2 and diacylglycerol O-acyltransferase 2 in CLA fed mice, both necessary for triglyceride biosynthesis. Expression of B-cell leukemia⁄lymphoma 6, a nuclear transcriptional repressor, and signal transducer and activator of transcription 5B, a transcription factor, were shown to be greater in the liver of CLA fed mice. Both genes are associated with immunoregulation. Comparing real-time RT-PCR to microarray data suggest a Bonferroni correction to microarray data is necessary in order to eliminate false positive data. Further verification of microarray results is needed to validate microarray data after a Bonferroni correction.
Date: 2008-08-18
Degree: MS
Discipline: Animal Science

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