Fig. 2. Loss of Hoxa3 and Hoxd3 results in ectopic expression of Hoxb1 in r6 with normal rhombomere periodicity. (A-D) Coronal hindbrain sections, immunolabeled for Hoxb1 of E11 control and mutant embryos with incremental loss of Hoxa3 and Hoxd3 alleles. (E,F) Coronal hindbrain sections of E11 control and Hoxa3^-/-d3^-/- double mutant embryos labeled for Hoxb1 (red), Hoxb4 (green) and TuJ1 (blue). Hoxb4 labels the boundary between r6 and r7. The VIIth and VIIIth cranial sensory ganglia (VII/VIII) are located ventrolateral to r4 and anterior to the otic vesicle (OV), which borders r5 and r6. (G-L) Coronal hindbrain sections of E9.25 control and Hoxa3^-/-d3^-/- double mutant embryos labeled for Hoxb1 (G,H), Krox20 (I,J) and Hoxb4 (K,L). Hoxb1 is expressed in r4 and in migrating neural crest cells (NCC). The otic vesicle (OV) borders r5 and r6. The bracket in H highlights the ectopic expression of Hoxb1 in r6. The arrows in K and L represent the boundary between r6 and r7.

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