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Fig. 5 Requirement of IrxB genes for pharyngeal pouch formation. (A) Confocal images show three bilateral streams of sox10:dsRed+ CNCCs (numbered) and her5:GFP+ endoderm in wild-type sibling controls and IrxBa−/−; IrxBb+/− mutants at 16.5 hpf. (B,C) Lateral views show loss of her5:GFP+ posterior pouches (green, numbered) and reduced numbers of sox10:dsRed+ neural crest-derived arches (magenta, numbered) in IrxBa−/−; IrxBb+/− mutants versus wild-type sibling controls at 24 and 36 hpf. (D) In situ hybridization reveals co-expression of irx3a with the ectomesenchyme marker dlx2a in the third and fourth pharyngeal arch, as well as the intervening dlx2a-negative regions (arrows) where endodermal pouches are located. Boxed region is magnified on the right. b, brain; e, endoderm; Y, yolk. n numbers denote individual embryos in which the indicated patterns were observed. Scale bars: 100 µm.