136. A Targeted 450 Kb Deletion in Mouse Chromosome 11 Identifies a Novel Gene Dramatically Impacting on VLDL Triglyceride Production 

Yiwen Zhu, Miek Jong, Elaine Gong, Kelly Frazer, Jan-Fang Cheng, and Eddy Rubin  
Department of Genome Sciences, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720  
Yzhu@lbl.gov 

In order to multiplex the examination of the function of genes present within JGI sequenced regions of the human genome the Cre Lox system was employed to delete several genes at a time within the human 5q31 / mouse chromosome 11 syntenic region. A 450 Kb stretch between IRF1 and CSF-GM gene containing nine genes, all of no known function, were deleted in ES cells. Mice homozygous for the deletion though prenatal viable demonstrated premature morbidity with approximately 75% dying before 100 days of age. The other significant finding in these animals was massive enlargement of the liver owing to the engorgement of hepatocytes with triglycerides. Plasma triglyceride levels were approximately ten-fold greater than control animals.  

Due to the importance of triglyceride metabolism as an atherosclerotic risk factor we investigated the mechanism underlying the hypertriglyceridemia in these mice. Of the three major factors effecting plasma triglyceride levels (synthesis, lipolysis in the periphery and clearance via hepatic uptake) abnormalities were only present with regard to synthesis. Homozygous animals exhibited a four-fold increase in hepatic VLDL triglyceride production while animals heterozygous for the deletion had a two-fold increase in triglyceride production compared to control mice. These deletion mice represent a unique model of enhanced hepatic triglyceride production coupled with increased hepatic fat accumulation.  

To identify the gene responsible for this phenotype through in vivo complementation the 450 Kb deletion mice were crossed with mice containing human YAC and mouse BAC transgenes covering the entire deleted region. Animals homozygous for the deletion and hemizygous for the transgenes were analyzed with regard to the phenotypes associated with the deletion. A human YAC containing approximately 120 Kb of the deleted region successfully corrected the hepatic fat accumulation, hypertriglyceridemia and premature lethality associated with the homozygous deletion. Three potential candidate genes are present in YAC: two identified as EST hits with no homology with known genes and one with homology to a rat liver specific transporter-like protein.