Fig. S1

Hindbrain rhombomere identity and boundary formation is disrupted in hoxb1b^/ mutant embryos. (A) In situ hybridization of hoxa2 in wild-type and hoxb1b/ embryos at 22hpf. Note lack of hoxa2 signal in second branchial arch neural crest domains (arrows). Otic vesicles are circled. (B) In situ hybridization of dlx2a and egr2 in wild-type and hoxb1b^/ at 22hpf with less organized and fused neural crest streams (arrows) in the first (I) and the second (II) arch. (C) Alcian green preparations of branchial jaw cartilages from wild-type and mutant larvae showing single elements: M=Meckel’s, PQ=palatoquadrate, CH=ceratohyal, HS=hyosymplectic. Note fusion of first pharyngeal arch Meckel’s cartilage and 2nd pharyngeal arch ceratohyal cartilage (arrow). (D) Rhombomere boundary marker sema3gb reveals that anterior hindbrain boundaries between r2 and r5 are lost in hoxb1b^/ embryos. (E) Onset of egr2 in r3, r5 of Tg(egr2b:KalTA4) live embryos. Start (0h) at about 5 somites. Fluorescence intensity in pseudocolors. Note single egr2-positive cells out of register (arrows) in hoxb1b/. (F) Reticulospinal neurons in larval hindbrain demonstrating requirement of Hoxb1b for rhombomere 4-specific Mauthner neurons (asteriks) in r4. (G) Requirement of Hoxb1b in single cells to contribute to anterior r3, r4 hindbrain segments in chimeric embryos. Donor cells from wild-type and hoxb1b^/;Tg(h2a.f/z-GFP) donor fluorescent dextran injected embryos (green) transplanted into wild-type Tg(egr2b:KalTA4) which expresses mCherry in r3 and r5 (purple). Note sorting out of hoxb1b^/ r3, r4 and r5. (H) Anterior lumen morphology at 23hpf upon injection of 750pg hoxb1b mRNA per embryo into wild-type (hoxb1b+/+ and hoxb1b^+/) (n=62) and hoxb1b^/)(n=21) embryos when compared to control wildtype (n=65) and hoxb1b^/ (n=13) embryos. Anterior-posterior axis marked by double arrows in all panels.