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Fig. 5 Misexpression of pou3f3b in posterior arch mesenchyme induces ectopic posterior-directed cartilages. Cartilage (blue) and bone (red) staining reveals ectopic cartilaginous projections in the third and fourth arches (Insets) of fli1a:Gal4VP16; UAS:pou3f3b (A) and kat6a−/− (B) larvae. The hyoid skeleton was reduced in fli1a:Gal4VP16; UAS:pou3f3b embryos (arrows in A) and homeotically transformed in kat6a mutants (arrowheads in B). (C and E) In situ hybridization for pou3f3b (pink) relative to the pan-mesenchyme marker dlx2a (green) shows ectopic expression of pou3f3b in neural crest-derived mesenchyme (primarily arches 1 to 4) in fli1a:Gal4VP16; UAS:pou3f3b embryos and in the dorsal third and fourth arches (double arrows) of kat6a mutants. (D and F) In situ hybridizations show that the PEM marker shha remains confined to the hyoid arch (arrow) in fli1a:Gal4VP16; UAS:pou3f3b and kat6a−/− embryos. In situ images are maximum-intensity projections. (Scale bars: A and B, 50 μm; C–F, 20 μm.)