This transgene comprises two tandem copies of a 0.7-kb DNA fragment containing the node-specific enhancer (NDE) of the Nodal gene, 1.2 kb of 5' flanking DNA from the Nodal locus containing the promoter, and the Cre recombinase coding sequence. Beta-galactosidase expression in progeny of mice with this transgene and animals bearing a lacZ Cre reporter transgene is first detected by X-Gal staining in the region of the posterior node of 2-somite-stage embryos; this activity becomes stronger as the embryos develop. (J:82703, J:104881)