Figure 7. Nuclear division with and without spindle microtubules.

Top panel: at the beginning of mitosis, chromosomes condense, detach from the SPB, and attach to spindle microtubules that emanate from the SPBs to form a bipolar array. Extension of the spindle and motor driven movement of chromosome along the spindle microtubules results in two daughter nuclei with equal chromosomal segregation. Lower panel: absence of spindle microtubules (+MBC), chromosomes remain associated with the SPBs and upon loss of cohesion are drugged away from each other by the movement of the SPB in the nuclear envelope. Actin depolymerization (+MBC +LA) blocks SPB separation, nuclear fission, and membrane ruffling.