A targeting vector containing a FRT flanked PGK-NEO cassette and a loxP site was inserted downstream of exon 41. A second loxP site was inserted upstream of exon 41. Mutant mice were bred with Tg(ACTFLPe)9205Dym mice (on a C57BL/6 congenic background (N10)) to remove the neo selection cassette. (J:101977)