Emx1-specific expression of foreign genes using "knock-in" approach

Emx1 is a mouse homologue of the Drosophila homeobox gene empty spiracles. Its expression is limited to the neurons in developing and adult cerebral c ortex and hippocampus. Because of the highly restricted expression pattern of the Emx1 gene, it would be quite desirable to characterize the promoter of the Emx1 for directing foreign gene expression in the transgenic mouse, We report here that me have achieved the Emx1-specific expression in transg enic mice by inserting the lacZ reporter and cre genes directly into the ex on 1 of the Emx1 gene using embryonic stem (ES) cell technology. The distri bution of the beta-galactosidase activity in the transgenic mice was consis tent with the published results obtained using in situ hybridization and im munohistochemistry. Furthermore, we have demonstrated that Cre protein was present in the cerebral cortex of the transgenic mice and was able to media te loxP-specific recombination in vitro, The creation of this line of cre t ransgenic mice, and the demonstration that the insertion site located in th e exon 1 of the Emx1 gene could render foreign genes a specific expression pattern restricted to the developing and adult cerebral cortex and hippocam pus, should be conducive to further studies of the effect of a gene mutatio n or overexpression upon the development and plasticity of cerebral cortex and hippocampus. (C) 2000 Academic Press.