Fig. 5. vHnf1 is required to define r4/r5 gene expression boundary in mouse embryos. (A,B) Dorsal and lateral views of Hoxb1 expression in wild-type and conditional vHnf1^–/– embryos. The normal r4/r5 boundary of Hoxb1 expression is indicated in wild-type embryos. vHnf1^–/– embryos exhibit expansion of Hoxb1 expression posterior to the r4/r5 boundary in the hindbrain (brackets).