Just as our bodies have skeletons, so do our cells. They're equally indispensible（不可缺少的） in both cases. Without our bony skeletons we'd go limp and fall down. And without our cytoskeletons（细胞骨架）, our cells, which come in roughly 200 different shapes and sizes, would all become tiny spheres（球体） and stop working. Using cells from the stem of a seedling as a model system, Ram Dixit's lab at Washington University in St. Louis seeks to understand the molecular mechanisms that organize and pattern the hundreds or thousands of microtubular "bones" of the plant cytoskeleton. In their model system, the microtubules form parallel bands like barrel hoops（桶箍） around the cell's girth.

Dixit's lab shows in the Oct. 24 online issue of Current Biology that misaligned microtubules that grow over existing microtubules are cut at the crossovers by the enzyme katanin（剑蛋白）, named for the katana, or samurai sword. Once a microtubule is cut, the part downstream of the cut falls apart, disintegrating into individual tubulin（微管蛋白） units.

Because katanin shows up at crossovers just before a microtubule is cut and because there is no cutting in a mutant plant line lacking katanin, the WUSTL scientists are sure that katanin and katanin alone is responsible for this activity. In the mutant the microtubules form disorganized cobwebs（蜘蛛网）.

The scientists also showed, by chilling cells to destroy their cytoskeletons, that katanin organizes the cytoskeleton in the first place as well as maintains its organization once it has formed.