Mtor is part of a dynamic nuclear derived spindle matrix distinct from MTs. (A) An S2 cell stably expressing Mtor-mCherry (red) and GFP–α-tubulin (green). (A′) The corresponding Mtor-mCherry channel alone. (B) S2 cell stably expressing Mtor-mCherry and GFP–α-tubulin upon colchicine addition (time = 0). (C–E) Live cell analysis of GFP–α-tubulin, Mtor-mCherry, and Jupiter-GFP after colchicine treatment. (C′) Loss of GFP–α-tubulin fluorescence in the spindle is accompanied with equivalent fluorescence gain in the cytoplasm. (D′) Mtor-mCherry fluorescence in the spindle is not affected by MT depolymerization. (E′) Jupiter-GFP fluorescence is lost from the spindle to the cytoplasm after MT depolymerization. (F–F″) Endogenous Mtor after cold-induced MT depolymerization. (G and G′) Lamin B localization around the spindle. F.I., fluorescence intensity. Time is shown in minutes/seconds. Bars, 5 µm.