Fig. 2

Chd expression is not sufficient to induce the formation of complete head structures in ichabod embryos. (A–D) Phenotypic observation of ichabod embryos at 24 hpf. Embryos were classified using the phenotypic classification criteria reported by Kelly et al., 2000 ;  Maegawa et al., 2006: Class 1 embryos show a severe ventralized phenotype; embryos develop neither a head nor a trunk. Class 1a embryos develop a partial trunk and spinal cord but no head structures; class 2 embryos develop a spinal cord and hindbrain but lack head structures anterior to the midbrain; class 3 embryos develop a defective forebrain and no eyes; class 4 embryos develop complete head structures but no notochord; class 5 embryos have no apparent deficiencies and survive until they are adults. (A) Uninjected ichabod embryos showed a ventralized phenotype, and were classified as a class 1 phenotype (22/22). (B) Upon injection with FGF8 mRNA, ichabod embryos showed a class 4 phenotype (14/20). (C) The majority of the ichabod embryos that were injected with chd mRNA were classified as a class 3 phenotype (14/20). (D) Ichabod embryos injected with β-catenin mRNA showed a class 5 phenotype (18/22). Scale bar represents 100 µm.