Fig. 2

Class II Hh regulated genes in zebrafish: nkx2.9 and nkx6.2 expression and regulation by Hh. (A and B) Lateral views of 36 hpf embryos, eyes removed, dot marks optic recess. (A) nkx2.9 is expressed in the ventral hindbrain, ventral midbrain and diencephalon in a pattern nearly identical to that of nkx2.2a (see Karlstrom et al., 2003). No nkx2.9 expression was seen outside the nervous system up to 36 hpf. Inset shows expression of nkx2.9 in the CNS at the tailbud stage (10 hpf). (B) nkx6.2 is expressed in the ventral hindbrain and ventral midbrain, but is not expressed in the forebrain. In the hindbrain, nkx6.2 is expressed dorsally, presumably in cranial motor neurons (arrows). Inset shows nkx6.2 expression in the ventral CNS at tailbud stage (10 hpf). (B′) Side view of somites 4–7 in the trunk showing nkx6.2 expression in the developing pancreas at 36 hpf. (C–H) Spinal cord cross-sections of 24 hpf embryos. (C) nkx2.9 is expressed in lateral floor plate cells, but not in the medial floor plate (*), similar to nkx2.2a (F). nkx2.9 expression is dorsally expanded in shh mRNA-injected embryos. The expression of nkx2.9 is lost in smu(smo), con(disp1), yot(gli2DR), and dtr(gli1) mutants. (D) nkx6.2 is expressed in the ventral half of the CNS. In shh mRNA-injected embryos nkx6.2 expression is expanded dorsally. nkx6.2 expression is completely absent in smu(smo) mutants. In con(disp1) mutants, nkx6.2 expression is absent dorsally but remains in the medial and lateral floor plate (arrowhead). In yot(gli2DR) and dtr(gli1) mutants, nkx6.2 expression is absent from the floor plate (arrowheads), but expression remains more dorsally. (E) nkx6.1 is expressed in lateral floor plate cells, in motor neuron precursors and in most ventral interneuron progenitors. nkx6.1 expression is dorsally expanded in shh mRNA-injected embryos and is absent in cyclopamine treated embryos. The expression of nkx6.1 is not affected in yot(gli2DR), and dtr(gli1) mutant embryos. (F) nkx2.2a is expressed in the ventral-most cells of the CNS, including the lateral floor plate but not the medial floor plate (*). (G) hlxb9 is expressed in developing motor neurons just dorsal to the floor plate. hlxb9 expression is undetectable in con(disp1) (inset) and smu(smo) mutants and highly reduced in yot(gli2DR), and dtr(gli1) mutants (data not shown). (H) olig2 is expressed in the ventral spinal cord, including in MN precursor cells (pMN). The expression of olig2 is dorsally expanded in shh mRNA-injected embryos and absent in cyclopamine treated embryos. olig2 expression appears unaffected in yot(gli2DR), and dtr(gli1) mutants. di, diencephalon; fb, forebrain; hb, hindbrain; mb, midbrain; nc, notochord; s, somite; t, telencephalon. * Marks the medial floor plate cells. Double-ended arrows in each panel show dorsal and ventral extent of gene expression. Scale bars: (A and B), 50 μm, (C–H) 15 μm in large panels, 24 μm in smaller panels.