The transgene consists of the chicken beta-actin promoter and the CMV immediate-early enhancer, a loxP flanked STOP cassette, and the full-length mouse Bmp4 cDNA followed by an Ires-EGFP sequences. Excision of the STOP cassette by cre recombinase permits expression of Bmp4. Five lines were generated: 1, 2, 3, 4, and 5.