The targeting cassette consisting of a SA.lox.PDGFRb.lox-Flpo-attB-Neo-attP cassette replaced the exons 2-4 of the endogenous Pdgfrb gene. The PDGFRb is a mouse Pdgfrb gene cDNA. PhiC31 integrase removed the attB-Neo-attP cassette. Cre-mediated recombination is required to achieve expression of the flpo recombinase. (J:306160)