Expression of the zic2 gene in chick embryos at HH stages 6+ to 12. A: zic2 is expressed in all of the head fold and neural plate region of stage 6+ embryos. B: At stage 8, zic2 expression continues in the neural folds and throughout the neural plate along the entire anterior-posterior axis of the embryo. C: zic2 expression is downregulated in much of the forebrain and midbrain regions of stage 9 embryos. zic2 expression persists in a small domain of the forebrain and in a large region of the hindbrain. Contiguous with its expression in the hindbrain, zic2 is expressed in the trunk neural tube. D: zic2 is not yet expressed in somites of stage 10 embryos. E, F: dorsal view (E) and side view (F) of stage 11 embryo; although zic2 expression appears weaker in the mesencephalon region (E), the side view shows that zic2 expression is present along the entire dorsal brain and trunk neural tube (F). The optic vesicles express zic2 at stage 11. G: Weak zic2 expression begins in the anterior somites of stage 11 embryos. H: zic2 is expressed in the most posterior neural tube and neural folds. I: in stage 12+ embryos, zic2 expression in anterior somites is more robust and zic2 is expressed in the periotic mesoderm (bracket). Overall, expression levels of zic2 are very low in early stage embryos. Abbreviations as in legend for Figure 1; NP: neural plate; black arrows: somites not expressing zic2; black arrowheads flank somites expressing zic2; bracket: periotic mesoderm.