A mouse PAC clone (RPCI21-546M3) containing the Pdgfra gene was modified by the insertion of a tamoxifen-inducible cre recombinase gene into exon 2 together with an frt flanked chloramphenicol selection cassette that was subsequently excised. Eleven founders were produced, only two of which expressed cre as expected. The more strongly expressing transgene line is used as the representative.