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Fig. 1 Hdac1 is required to establish and maintain stripes of erm expression within the centres of hindbrain rhombomeres 2-7. In situ hybridisation analysis of erm expression in (A,C,E,G,I,K) wild-type sibling and (B,D,F,H,J,L) homozygous hdac1 mutant embryos, at 21 hpf (A-D), 24 hpf (E-J) and 31 hpf (K,L). Lateral views show significant reduction of erm expression in the hindbrain of hdac1 mutant embryos (B,F) compared to wild-type siblings (A,E). Dorsal views of hindbrain are shown in panels C,D,G,H. Transverse sections through rhombomere 5 are shown in panels I,J,K,L. The hindbrain of wild-type sibling embryos (C,G,I,K) exhibits robust stripes of erm expression at 21 and 24 hpf that are restricted to rhombomere centres (C, G). Both the ventricular zone and mantle region of the hindbrain express erm at 24 hpf, but by 31 hpf erm expression is restricted to the ventricular zone. In hdac1 mutant embryos erm is expressed at 21hpf in a weak, more diffuse domain that encompasses rhombomeres 4, 5 and 6. By 24hpf, erm expression is extinguished in all rhombomeres of the hdac1 mutant hindbrain apart from rhombomere 4.