Specificity and efficiency of cre-mediated recombination in Emx1-Cre knock-in mice

Emx1 is a mouse homologue of the Drosophila homeobox gene empty spiracles a nd its expression is restricted to the neurons in the developing and adult cerebral cortex and hippocampus. We reported previously the creation of a l ine of transgenic mice in which the cre gene was placed directly downstream of the putative Emx1 promoter using ES cell technology. We showed that Cre protein was present in the cerebral cortex of the transgenic mice and was able to mediate loxP-specific recombination in vitro. In the present study, the specificity and efficiency of the cremediated recombination were deter mined using three independent lines of reporter mice and a combination of h istochemical staining, neuronal culture, and Southern detection of the geno mic DNA, Our results showed that the recombination was highly efficient in all three lines of reporter mice tested and confirmed that the deletion was restricted to the neurons in the cerebral cortex and hippocampus. Furtherm ore, we have determined that the recombination efficiency in the cerebral c ortex was 91%. Our results suggest that Emx1 is not expressed in every neur on in the developing and adult cerebral cortex. This line of cre mice shoul d contribute to the studies of cortical development and plasticity. (C) 200 0 Academic Press.