Third instar larval brains were fixed and stained as described previously (Martinez-Campos et al., 2004 (link)). For drug treatment, dissected brains were incubated for 2 h at 25°C in PBS containing 1 μg/ml colchicine before fixation. The following primary antibodies were used: rabbit anti–D-PLP at 1–2 μg/ml (Martinez-Campos et al., 2004 (link)); mouse anti–α-tubulin at 1:1,000 (DM1α; Sigma-Aldrich), mouse anti–γ-tubulin at 1:1,000 (GTU88; Sigma-Aldrich), and mouse anti–phospho-Histone H3 at 1:2,000 (Abcam). All secondary antibodies coupled to the appropriate fluorophore (Alexa 488 or 568; Invitrogen) were used at 1:1,000 in PBT. Fixed preparations were examined on a widefield upright microscope (Axioskop II; Carl Zeiss MicroImaging, Inc.), equipped with a camera (CoolSnap HQ; Photometrics) and MetaMorph software (Molecular Devices), using a 100×/1.3 NA objective. Images of fixed brain cells are all maximum intensity projections of optical sections acquired at 0.1– 0.2-μm intervals.