Fig. 8. An `En code' can account for genetic partitioning of the midbrain and cerebellum vermis into functionally related domains. (A) Schematic illustrating the domains (color coded) within the mouse early neural tube (left) along the A-P axis that express either or both of the En genes, and the regions of the adult cerebellum and midbrain (right) that they give rise to owing to a rotation of the neural tube. The red-outlined region delineates rhombomere 1. (B) Schematic illustrating the normal gene dosage requirement for En1 and En2 in sustaining development of distinct domains of the tectum and Cb. Note that based on a sensitive knock-in assay, En2 protein appears to be more active throughout the vermis than En1. Thus, the gene dosage effects are likely to reflect differences in En1 and En2 gene expression. Cb, cerebellum; Mes, mesencephalon; SC, superior colliculus; IC, inferior colliculus; A, anterior; P, posterior; M, medial; L, lateral.