Spindle angle determination was performed as previously described (Finegan et al, 2018 (link)). Angles were determined by drawing a first line connecting either the two spindle poles (if applicable) or along the spindle and a second line along the apical surface of the tissue, then measuring the angle between them. Spindle angle values for control w1118 are reused between Figs 1D, 3F, 4C, 5C and 6F, and for pinsp62/pinsp62 between Figs 3F, 4C and 5C.