A 1.5 kb fragment encoding the Dll1 mesoderm-specific enhancer element (Dll1-msd) was cloned into a plasmid (pAKH) upstream of the beta-globin miminal promoter, and nuclear-localized cre recombinase (NLS-cre) and the beta-actin polyadenylation signal. The linearized purified fragment was microinjected into fertilized FVB/N eggs. Two founder lines were established with similar cre activity domains. Line 33 was chosen for further characterization. (J:148512)