The rhombomere 5 region is broadened in the rSey2/ rSey2 hindbrain. (A-F) The expression sites of Hoxb1 and Krox20 (blue) were compared with that of Cyp26b1 (red) in WT (A, D), rSey2/+ (B, E) and rSey2/rSey2 (C, F) hindbrains. (A-C) Hoxb1 expression (as a marker of r4) is unchanged in the rSey2/rSey2 hindbrain (C). (D-F) Krox20 expression (as a marker of r5; cannot detect in r3 at E11.5) overlaps with Cyp26b1 expression in the dorsolateral domain of the WT and rSey2/+ hindbrain (D and E). The r5 region is slightly broadened in the rSey2/rSey2 hindbrain along the anterior-posterior axis (F). (G-I) EphA4 expressed in both r3 and r5 of the E11.5 hindbrain. EphA4 expression domains (blue) are broadened only within the r5 region of the rSey2/rSey2 hindbrain (I) as compared to the WT (G). (J-L) The expression site of RARβ (blue) was compared with that of Krox20 (red) in WT (J), rSey2/+ (K) and rSey2/rSey2 (L) hindbrains. Krox20 expression is posteriorly expanded in the rSey2/rSey2 hindbrain (L), although the anterior border of RARβ expression (anterior edge of r7 in L) is not altered. Scale bar: 500 μm.