Laser ablation reveals how the mitotic spindle reshapes the fission yeast nucleus

When eukaryotic cells divide, the mitotic spindle, a self-assembling microtubule-based machine, segregates chromosomes to each daughter cell. In organisms with closed cell division, such as the fission yeast S. pombe, the nuclear envelope remains intact. Thus, the spindle must accomplish its feat from under an additional mechanical constraint. In the case of S. pombe, spindle elongation is accompanied by a series of nuclear shape changes. The nucleus begins as a single spheroid, passes through peanut- and then barbell-shaped forms, and pinches off into two new daughter nuclei. While spindle elongation clearly helps drive these shape changes, how the nuclear envelope and spindle coordinate is not clear. To test the mechanical interactions between the envelope and spindle, we use targeted laser ablation to sever the spindle and to rupture the envelope, and examine the ensuing responses by live cell confocal fluorescence microscopy. We combine the targeted damage of laser ablation with genetic and biochemical perturbations that further affect mechanics, such as by increasing or decreasing envelope membrane tension or by altering spindle elongation dynamics. These readouts allow us to begin mapping how the spindle and nuclear envelope shape each other as the cell divides.