Dlg1 is required for planar spindle orientation in chick neural progenitors. (A) Scheme of flat mounting of the E3 (Hamburger Hamilton [HH] stage 18) chick neural tube for en face imaging of neuroepithelial cells. (B) GFP-Dlg1 is restricted to the basolateral cortex during metaphase. The z view is a reslice along the z axis of the confocal stack acquired in en face view. The four bottom images show single optical sections from the en face view (apical and middle levels). ZO-1 (red) labels tight junctions. White dashed lines on the z view show focal planes chosen for the apical and middle en face views. White stars show apical domain of the GFP-Dlg1–expressing cell. (C) Z view along the axis of the mitotic spindle of metaphase and anaphase cells expressing control (Ctrl) or Dlg1-targeting miRNAs (H2B-GFP marker). H2B-GFP and γ-tubulin label chromosomes and spindle poles, respectively. (D) Quantification of mitotic spindle α_z orientation at E3, 24 h after electroporation (means ± SEM, n > 50 cells from at least three embryos). **, P ≤ 0.01; ***, P ≤ 0.001. (E) Tissue architecture (top) and apicobasal polarity (cell resolution images) are not affected in neural tubes electroporated with Dlg1 miRNA as illustrated by ZO-1, β-catenin, or N-cadherin staining. White arrowheads point to H2B-GFP–positive electroporated cells. Dotted lines highlight the contour of the neural tube (top) or of individual dividing cells (bottom). Bars: (A) 1.5 mm; (B and C) 5 µm; (E, top) 50 µm; (E, bottom) 10 µm.