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Fig. 6 Nodal signalling promotes early asymmetric neurogenesis. (A-D) Confocal projections of Tg(huC:gfp) transgenic zebrafish embryos incubated with DMSO (A,C) or with SB431542 (B,D) from 10 hpf and fixed at 34 (A,B) or 38 (C,D) hpf. Arrows indicate that the left pools of HuC+ neurons are bigger than those on the right in DMSO-treated embryos (A,C), whereas the left and right pools are symmetric in embryos incubated with SB431542 (B,D). The epiphysis is indicated by a blue line. Habenular neurogenesis is also delayed in SB431542-treated embryos. (E-H) Numbers of left and right HuC+ habenular neurons (E,G) and corresponding AI (F,H) in embryos treated with DMSO or SB431542 at 10 (E,F) or 16 (G,H) hpf. Habenular neurons were detected in Tg(huC:gfp) transgenic embryos using an anti-GFP (E) or HuC/D (G) antibody. A symmetry line (black) is included as a reference in E and G. Dotted lines represent best-fit linear regressions. Horizontal black lines in F and H indicate the median AI value for the group of like-treated embryos.