Fig. 1. Dynamic expression of En1^lacZ and En2^tau-lacZ in the mes/r1 of mouse embryos. En1 (A) and En2 (G) mRNA expression detected by whole-mount RNA in situ hybridization. (B-F) En1-lacZ and (H-L) En2-tau-lacZ expression at the indicated stages detected by ß-gal analysis. En1 is induced earlier and becomes more restricted than En2 by E10.5. Staining in the fourth ventricle in I and D is a result of probe trapping. CbP, cerebellar primordium; mes, mesencephalon; Mb, midbrain; r1, rhombomere 1.