Fig. 4. Ngn2 is required for Th⁺ DA neuron generation, and Mash1 partially compensates for Ngn2 function in the ventral midbrain. Coronal sections showing the expression of Th in DA neurons in the ventral midbrain of (A) wild-type and (B-D) mutant E14.5 mouse embryos. A severe reduction in Th⁺ DA neuron number in (B) Ngn2^-/- and in (C) Ngn2^-/-;Mash1^-/- mutant embryos is observed, which is not evident in (D) Mash1^-/- embryos, which have wild-type numbers of Th⁺ DA neurons. (E) Partial rescue in the number of Th⁺ DA neurons in Ngn2^{KIMash1/KIMash1} (Ngn2^KIM1/KIM1) embryos. Modified, with permission, from Kele et al. (Kele et al., 2006).