Fig. 4. Rostral expansion of trigeminal ganglia, the MHB domain, and the premigratory neural crest cells correlates with expansion of iro1 and iro7 in headless (hdl) mutants. (A,B) Expression of iro1 (A) and iro7 (B) is expanded rostrally in hdl mutants at the tailbud stage. (C-E) The trigeminal ganglia (C), MHB domain (D) and neural crest (E), marked respectively by ngn1 expression at the one-somite stage (C), pax2.1 at the three-somite stage (D) and fkd6 at the tailbud stage (E), are expanded rostrally in hdl mutants. Expression of krox20 (krx20) in the hindbrain is unaffected in hdl (D). Red arrowheads indicate anterior limit of expression of each gene in wild-type embryos for comparison.