Sip1 is expressed in the developing neural and neural crest cells. (A–H) Whole-mount in situ hybridization of chick embryos at various stages using an antisense probe to Sip1 reveals expression in the developing neural plate (A–C), neural tube (D–H), and premigratory and migratory NC cells (F–H) at stages HH4–HH16. Sections of embryos at indicated axial level are marked by dashed lines (c′, f′, and g′). Sip1 is expressed throughout the neural plate, neural tube, and in migratory NC cells (arrow). (g′) Top panel is Sip1 expression and bottom panel is HNK1 expression in same section showing overlap with migratory cells (arrow). (g′′) Whole-mount immunohistochemistry showing that Sip1 protein is localized to the same tissues as Sip1 transcript. Bars: (A–H) 200 µm; (c′–g′′)100 µm.