Comparison of zic1-4 gene expression in chick embryos at stage HH 14/15. A-D: side views of whole embryos; E-H: dorsal views of midbrain, hindbrain, anterior trunk; I-L: mid-trunk; M-P: tail with epithelial somites marked (I - V). A, E, I, M: zic1 is expressed in the dorsal brain and in the neural tube, except in the most posterior neural tube (M). zic1 is expressed in most somites. B, F, J, N: zic2 is expressed along the entire dorsal brain and neural tube of the trunk with enhanced expression in the neural tube of the tail (N). zic2 is expressed in the developing eye (B), in the periotic mesoderm (F) and in anterior somites (F). C, G, K, O: zic3 is expressed in the dorsal brain, in the eye (C), and in the neural tube, except in the neural tube of the tail (O). zic3 is expressed in the presomitic mesoderm (O). D, H, L, P: zic4 is expressed in the anterior brain (D) and is not detectable in any other parts of stage 14/15 embryos. Pro: prosencephalon; Mes: mesencephalon; Rhom: rhombencephalon; ov: otic vesicle; NT: neural tube; PSM: presomitic mesoderm; arrowheads outline somites; arrow points to zic4 expression; bracket: periotic mesoderm. The stage of the embryos is HH 14 with the exception of D, H: HH 14-; M, F, N, P: HH 15.