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Fig. 2 Temporally controlled sim1a knockdown reveals medial displacement of dopaminergic longitudinal projection tracts. Dorsal views of confocal z-projections of 72 hpf embryos at the anterior-posterior levels of forebrain (A,C,E,G) and hindbrain (B,D,F,H). (A,B) Control MO injection. (C,D) sim1a morpholino injection: TH immunoreactivity is lost in cell bodies (C) and axons (D) of the DA HTS systems (DA groups 2,4-6). (E,F) Caging the sim1a morpholino results in wild-type-like formation of DA HTS systems. (G,H) Temporally controlled activation of sim1a MO at 22 hpf permits the formation of individual group 2,4-6 DA neurons (G) but causes a medial shift of TH-positive axons (arrows in H). Arrowheads in B indicate the position of TH-positive HTS tracts. Asterisks in B,D,F,H indicate TH-positive locus coeruleus (LC) neurons. Numbers in A,C,E,G indicate DA groups (Rink and Wullimann, 2002). (I) Quantification of mediolateral positioning of TH-positive HTS axons at 72 hpf at the level of LC neurons (IV in B); of distances of group 2 (I in A) and group 4 cells (II in A) from the midline; and of distances between LC neurons (III in B). ***P<0.0001; n.s., not significant. Scale bar: 50 μm.