Fig. 5. Emx2 is required for the formation of the RN in mice. (A,B) Brn3a+ cells are present in midbrain wholemounts of E14.5 heterozygous (A) and homozygous (B) mutant littermates, demonstrating that pRN neurons are initially specified in Emx2 mutants. (C-F) Brn3a (C,D) and class III ß-tubulin (E,F) gene expression fail to identify a RN at E18.5 in homozygous Emx2 mutant mice. (G,H) Normal Isl1 (G) and Th (H) gene expression in Emx2 homozygous mice at E18.5 suggests that among medial arc derivatives, the RN is selectively disrupted by mutations in the Emx2 gene. Aq, cerebral aqueduct.