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Fig. 1 Hh signaling activates six3b expression in the developing zebrafish forebrain. (A,B) At 15s, six3b is expressed normally in the anterior forebrain of vehicle-treated embryos (black arrowheads in A, 15/15 embryos) and dramatically reduced in cyclopamine-treated embryos (red arrowheads in B, 14/14 embryos treated from the 2- to 4-cell stage onwards). (C,D) At prim-10, ventral forebrain six3b expression is strong in wild-type (WT) embryos (black arrowheads in C, 67/92 embryos) and absent or greatly reduced in smo-/- mutants (red arrowheads in D, 25/92 embryos). (E-H) Embryos injected with a low amount of shha mRNA (12.5 pg) show expanded six3b expression [green arrowheads in H, 10/23 embryos, 2 experiments (n=2)], but no change in ptc1 (F, 31/31 embryos, n=2). Embryos shown in panels A-H are lateral views. Panels A′-H′ are ventral views of the same embryos, anterior to the left.