Fig. 7. Helt represses Ngn genes. (A) Expression patterns of proneural genes in the developing mouse mesencephalon. Expression of Ngns and Helt is mutually exclusive in all the domains. By contrast, Mash1 is expressed in essentially all domains and is coexpressed with Helt. (B) Ngn genes are selectively expressed in glutamatergic progenitors. Ngn1 is coincidently expressed in the VZ, where Brn3a⁺ neurons emerge. Ngn2 is selectively expressed by glutamatergic progenitors as well as dopaminergic progenitors. (C) Helt represses Ngn expression in the mesencephalon. In transgenic embryos expressing Helt under the control of the nestin enhancer, expression of Ngn1 and Ngn2 is repressed. By contrast, Mash1 expression is unaffected. (D) Ngns are ectopically expressed in presumptive GABAergic domains in the Helt-null mutant. At E11.5, Ngn1 and Ngn2 are ectopically expressed in the m2 to m4 domains in the Helt^-/- mutant. At E12.5, the Ngn expression in the dorsal m1 domain is upregulated and coexpression of GFP and the Ngns is observed (inset).