This transgene contains the cre recombinase coding sequence and the metallothionein 1 polyadenylation signal between the Wnt1 basic promoter and intron, which is followed by the inverted rhombomere 4 (r4) enhancer and the r3/r5 repressor from the Hoxb1 locus. These elements together restrict expression to rhombomere 4 in the hindbrain of the developing embryo. (J:20433, J:197162)