(a–e) HH-12 chicken neural tubes were electroporated with three different stable forms of β-catenin (β-cateninS37A, β-cateninΔ29–48 and β-cateninS33Y) at the level of the rhombencephalon (b) and the spinal cord (c–e). Transverse sections were stained with antibodies against GFP (green, transfection) and phalloidin (red, labels F-actin). The arrow in b indicates the invaginated epithelium, note the lower magnification in this panel. (f–h) Chicken embryos were analysed 16, 24, 36 or 48 h after electroporation with β-cateninΔ29–48 and transverse sections were stained with antibodies against GFP (green, transfection) and phalloidin (red). Panel g shows a scheme of how the apico-basal distance was measured in the cells forming invaginations. For each Id (invagination distance) measured on the electroporated side (EP), a Cd (control distance) was measured at the same dorso–ventral level on the non-electroporated side (NEP). Panel h shows a dot chart of apical-basal distances at different times after transfection. Scale bar, 50 μm.