Direct LGN–Dlg1 interaction is necessary for LGN cortical localization and mitotic spindle orientation. (A) Dlg1–LGN–Gαi functional domains. TPR, tetratricopeptide repeat; PDZ, PSD95/Dlg/ZO-1 domain. (B) GFP-LGN recruitment to the cell cortex is reduced upon Dlg1 RNAi (cytoplasmic RFP marker). (C) Localization of GFP fusions to linker (LR), GPR, and LR + GPR domains of LGN in E3 chick neural progenitors. White arrowheads point the weak cortical localization of the LR and GPR domains. (D) Serine at position 401 in LGN is necessary for the additive effect of the LR domain in LR-GPR cortical recruitment. Graphs in B and D show ratios of cortical over cytoplasmic GFP signals (means + SEM, n > 15 cells). (E and F) Mitotic spindle angle distribution in metaphase and anaphase for RNAi rescue experiments (means ± SEM). (G) Gαi and Dlg1 cooperate for LGN cortical recruitment and/or stabilization. Instructive polarity cues, either external (adhesion to substrate) or cell autonomous (possibly involving Dlg1 localization), and control LGN and NuMA polarization, resulting in spindle orientation, are depicted. It is not known whether Dlg1 and Gαi are mutually dependent for their cortical localization. Ctrl, control; wt, wild type. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001. Bars, 5 µm.
