Fig. 8. (A) Schematic representation of expression of genes in otic vesicles of the wild-type (left) and Six1^–/– mice (right) at E10.5. In the otic vesicle of the wild-type, otic genes are expressed in the specified regions represented in different colors. In the wild-type otic vesicle, Six1 is expressed in the ventral half of the otic vesicle. In the otic vesicle of Six1^–/–, the expression domains of Dlx5, Hmx3, Dach1 and Dach2 are expanded ventrally, and the expressions of the ventral marker genes (Otx1, Otx2, Fgf3 and Lfng) are lacking due to the absence of Six1. (B) Regulation of gene expression by Six1 in the ventral otic vesicle. Six1 activates the expression of ventral marker genes, Otx1, Otx2, Lfng and Fgf3, but represses dorsal marker genes, Dlx5, Hmx3, Dach1 and Dach2, and contributes to the patterning of the otic vesicle. D, dorsal; L, lateral; M, medial; V, ventral.