Functional perturbation of the lamin-B envelope interferes with spindle length changes and the completion of mitosis. (A) Microinjection of the lamin-B tail dominant-negative (DN) subfragment disrupts the lamin-B nuclear lamina and causes delays in prometaphase spindle formation, destabilization and length fluctuations of the phase I spindles, defects in subsequent spindle morphogenesis, and failure to complete mitosis. (B) The microinjection of a mixture of anti–lamin-B mAbs cross-links the lamin-B envelope into a hyperstable network that fails to disassemble. This structure impedes spindle elongation during prometaphase phase II and anaphase B (graph; arrows show times when still images were captured). In A and B, panels show still images at times after NEB. In A, t = 0 corresponds to NEB for spindle s1. Top and bottom graphs show pole–pole spacing versus time after NEB (t = 0) for multiple spindles (mean with SD) and individual spindles (A, second row: the left graph shows multiple control spindles [black]; for clarity, the right graph shows a single control spindle [black]). Bars, 10 μm.