PRODUCTION OF MOUSE MODELS FOR MALFORMATION BY GENE TRAP

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A strategy to monitor transcriptionally active regions of the genome was first described in bacteria in 1979. It involves the introdution of reporter into the genome that require the acquisition of cis-acting DNA sequences to activate reporter gene expression. This approach has been applied more recently in higher organisms using modified vectors suitable for eukaryotic transcription units. In the mouse unknown genes have been identified by insertional mutation in transgenic mice generated by retroviral infection or DNA microinjection. However, this approach is laborious and time-consuming. Through the use of embryonic stem (ES) cells, the enhancer traps as well as the gene trap are now possible in the mouse. In the trap vector bacterial lacZ gene is usually used as a reporter gene. However, this gene product is thought to exert toxic effect on certain types of cell. We fpoud that this toxicity was reduced by the target expression of b-galactosidase in the nucleus. Using the gene trap method, we demonstrated that new genes were identified in about 60% ES trap clones, and that the 3'region of flanking mouse genome was deleted of rearranged by insertion event in most of cases. We isolated 6 ES trap clones that showed expression of lacZ before induction of differentiatio by retinoic acid. The promoter region of the unknown gene, termed Ayul, was isolated from one of these trap clones. This gene is expressed in the nerve cell of brain, epithelial cells of sstomach and duodenum, and testis of adult mouse. b-galactosidase activity was also detected in the midgut of 8.5 day embry when the gastro-intesitinal tract starts to form, suggesting that the Ayul gene is involved in the formation of gastro-intestinal tract.