Selection of primary cell cultures with cre recombinase induced somatic mutations from transgenic mice.

Deletion of genes in defined cell types has been achieved using a combination of gene targeting techniques and the Cre- lox P recombination system. Here we present a method to selectively isolate genetically altered primary cell cultures based on the permanent activation of a drug-resistance gene by the Cre recombinase. Transgenic mice were generated harboring a dormant form of the hygromycin resistance gene. This mouse line was crossed with mice carrying a constitutive Cre gene and an endogenous floxed allele. Primary fibroblasts established from triple transgenic embryos displayed not only hygromycin resistance but also recombination of the endogenous floxed allele. These results prove the potential of this approach.