Fig. 3. The ectopic mDA progenitor domain in En1^+/Wnt1 mutants is established through partial repression of Nkx2-2 in the ventral hindbrain by Otx2. (A,B) Coronal sections of E12.5 wild-type and En1^+/Wnt1 (n=4) embryos at the height of rhombomere 1-2 (black bars in Fig. 1B) hybridized with probes for Wnt1, Shh, Otx2 (green), Th (red) and the serotonin transporter (Slc6a4, green), or immunostained for Otx2, Nkx2-2 and Th. Top row in A are bright-field pictures corresponding to the dark-field images. Pictures in A are partly pseudocolored overlays of the corresponding dark-field images. Brackets in B indicate the region where the most ventral part of the Nkx2-2 domain in the hindbrain was repressed by the ectopically induced Otx2. (C) Sketch of a cross-section through the En1^+/Wnt1 mutant rostral hindbrain at E12.5 summarizing these results. 5HT neurons were probably generated from the dorsolateral Nkx2-2-positive domain within the mutant BP in this region.