Specific expression of EYFP at the mid-hindbrain junction in a R26R-EYFP E8.5 embryo carrying En1Cki, an Engrailed-1 Cre knock-in allele. A, dark field illumination, showing anterior portion of embryo. B, YFP expression in the same embryo. The outline of the embryo is indicated by the dotted line. C, E8.5 embryo from a cross betweenEn1Cki and the R26R lacZ allele , resulting in lacZ expression in the same mid-hindbrain region.