The targeting cassette consisting of a SA.lox.PDGFRa.lox-Flpo-attB-Neo-attP cassette replaced the exons 2-4 of the endogenous Pdgfra gene. The PDGFRa is a mouse Pdgfra gene cDNA. PhiC31 integrase removed the attB-Neo-attP cassette. Cre-mediated recombination is required to achieve expression of the flpo recombinase.