Expression of validated Hoxb1a target genes with broad r4 expression domains. In situ hybridization at 20 hpf of hoxb1a (A) and eight Hoxb1a target genes (B–I). Anterior to the left in all panels. Rhombomere (r) 4 is labeled. Panels i and iv: In wild-type embryos, (A) hoxb1a is expressed in an r4 stripe, as are (B) fabp7a, (C) rarα2a, (G) col7α1l, (H) eaat2, and (I) evi1. Expression of (D) meis2.1, (E) zic1, and (F) zic4 is elevated in r4 as compared to the surrounding hindbrain tissue. The eight Hoxb1a target genes also have Hoxb1a-independent expression domains, such as the lower-level (E) zic1 and (F) zic4 expression along the length of the neural tube, and (H) the bilateral discrete domains of eaat2. Panel ii: In Hoxb1a-deficient embryos, (A) hoxb1a mRNA remains unaffected, however, the r4-specific expression of all eight Hoxb1a target genes (B–I) is missing or reduced. Panel iii: hoxb1a mRNA-injected embryos show a characteristic anterior expansion of (A) hoxb1a and (B–I) all eight Hoxb1a target genes into r2 and r3 (and some more anterior regions). Panel v: Transverse sections through wild-type embryos show that (A) hoxb1a, (C) rarα2a, and (D) meis2.1 are expressed throughout the DV extent of the neural tube. (B, E–I) The remaining six genes are expressed in varying subdomains along the DV axis. dors: dorsal; lat: lateral; MO: morpholino; ts: transverse.
|
