Fig. 1. Differential maintenance of Hoxa3 and Hoxb3 expression is conserved in mouse and chick embryos. (A-D) Dorsal views of flat-mounted mouse hindbrains (A,B) and chick hindbrains (C,D) hybridized with Hoxa3 (B,D) or Hoxb3 (A,C). (E-F) Lateral views of mouse (E,F) and chick embryos probed with Hoxa3 (F,H) or Hoxb3 (E,G). All mouse embryos and tissue were at stage 10.5 dpc, and chick embryos and flat-mounts at HH stage 16. The black arrowheads indicate the r4/r5 boundary. Note that in both species, Hoxb3 is downregulated in r5 and r6, while Hoxa3 is maintained in the anterior segments.