Fig. 1. Loss of vhnf1 function results in transformation of posterior hindbrain to r4 identity. (A-F) 14-somite stage embryos. (A,B) hoxb1a gene expression (purple) is limited to the future r4 domain in a wild-type background and krox20 expression (orange) is present in presumptive r3 and r5 (A). hoxb1a transcripts are expanded throughout the posterior hindbrain in vhnf1 mutants, whereas r5-specific krox20 expression is reduced or absent in vhnf1 mutants (B). (C,D) hoxb3 expression (purple) is present in future r5 and r6 in the wild-type background (C), but is not expressed in vhnf1 mutants (D). (E,F) hoxB4 expression (orange) has an anterior boundary of expression at the future r6/r7 boundary and occurs throughout the anterior spinal column in wild-type (E); myod expression (posterior purple stain) identifies the mesoderm underlying the spinal column (s1=somite 1) and krox20 shows r3 and r5 (purple). In vhnf1 mutants, the anterior boundary of hoxB4 expression is indistinct and posteriorized (F). (G-J) One-somite-stage embryos. (G,H) valentino expression in presumptive r5 and r6 in wild-type embryos (G) is missing in vhnf1 mutants (H). (I,J) The r5 stripe of krox20 expression is present in wild-type embryos (I) but is severely reduced in vhnf1 mutants (J). (K,L) Reticulospinal neurons visualized in 48 hour embryos using anti-neurofilament (RMO44) antibody. Mauthner neurons (arrowheads) are limited to the single r4-derived pair in wild-type embryos (K) but appear in additional, posterior locations in vhnf1 mutants (red arrowheads) (L). (A-F) Dorsal view, anterior to the left. (G-L) Dorsal view, anterior to the top.