Fig. 2

Ectopic formation of hindbrain in embryos lacking Cdx4 or Cdx1a/Cdx4. (A) Schematic presentation of genetic markers for the hindbrain and anterior spinal cord. Numbers indicate rhombomeres. (B-M) Expression of krox20 (B,C), hoxb1a (D,E), hoxa2b (F,G), valentino (val, H,I), hoxb4a and krox20 (J and K), krox20 and hoxb1a (L), or krox20 and valentino (M) in wild-type control (B,D,F,H,J) and cdx1a/4MO-injected embryos (C,E,G,I,K-M) at 22 hpf. (K-M) Higher magnification dorsal views of the posterior region are in the insets [bright-field images in K,L; bright-field (upper), fluorescent (middle) and superimposed (lower) images in M]. Ectopic expression of the hindbrain markers are indicated by arrowheads (C,E,G,I). In the posterior neural tissue of the cdx1a/4 morphant embryos, hoxb1a expression (r4, black arrowhead in L) was detected just posterior to the krox20 expression (r5, red arrowhead in L); valentino expression (r5, 6, black arrowhead in M) overlapped with krox20 expression (r5, red arrowhead in M) and extended anteriorly (krox20^-val⁺ domain corresponds to r6); the hoxb4a^- domain (r6, gray arrowhead in K) was anterior to the krox20 domain (r5, black arrowhead in K). (N) Expression of krox 20 in embryos that received 1 ng cdx4MO at 22 hpf. Higher magnification views in the inset. Ectopic expression domains are marked by arrowheads. (O-Q) Expression of krox 20, hoxb1a and valentino in embryos that received 1 ng cdx1aMO at 22 hpf. (R-W) Expression of krox20 at 13 hpf, of hoxb1a at 15 hpf and of valentino at 11 hpf in wild-type control (R,T,V) and cdx1a/4 morphant embryos (S,U,W). Ectopic expression domains are marked by arrowheads. Scale bar: 100 μm.