Lipid signal mediates mitotic effect of lipins. (A) HeLa cells stably coexpressing H2B-mCherry and GFP–lamin B1 were transfected with siRNA oligos against lipin 1–3 or control oligos and synchronized by double thymidine arrest. Approximately 30–60 min before mitotic entry, cells were supplemented with DMSO (mock) or 200 µM DAG, and mean lamin B1 disassembly was determined as in Fig. 2. (B) Mean mitosis durations of cells quantified in A. The data represent the mitotic events from three replicate experiments. n > 100 for each condition with *, P < 0.05 and ***, P < 0.0001 (U test; Table S2). Dotted lines indicate mean control timing. Error bars indicate 95% confidence intervals. (C) Model of lipid-mediated mitotic lamin disassembly. Dullard dephosphorylates and activates lipins that in turn produce DAG from phosphatidate. DAG activates cPKCs, which, in concert with CDK1, can trigger phosphorylation-dependent mitotic lamin disassembly. NPC, nuclear pore complex; Nups, nucleoporins; INM, inner nuclear membrane; PA, phosphatidate; P, phosphorylation.