A Study of the Effects of Microtubule Dynamics on Cytokinesis

Erin Donnelly
Boston College

The mitotic apparatus of a cell functions both structurally and biochemically throughout the cell cycle. The microtubules emanating from the centromsomes signal to the cortex of the cell, which positions the site of the cleavage furrow. This furrow is the location where the mother cell will ultimately divide into two daughter cells. Microtubules are dynamic, not static. They constantly polymerize and depolymerize, or grow and shrink, depending on the stage in the cell cyle. Using sea urchin embryos, I determined the effects that small-molecule drugs have on these microtubule dynamics. This helped me to study the role of the astral microtubules during cytokinesis. Treatment of the cells with hexylene glycol, a microtubule-stabilizing drug, results in early contact of the microtubules with the cell cortex. This causes an early initiation of cytokinesis. Many of these treated cells arrested, however, due to the inability of the microtubules to then depolymerize. The drug urethane increases catastrophe, the release of tubulin subunits from the microtubules. This prevents the growth of long astral microtubules at anaphase in these cells. The cells are able to complete mitosis, but they are unable to divide because of a shrunken spindle. Experiments completed by Laila Strickland, a graduate student in the laboratory, have shown that this tiny spindle is compitent to induce a furrow, however, when manipulated to come in contact with the cortex of the cell. I have also studied the plus-end binding proteins that may act as the signals from the microtubules to the cortex to position and initiate cell division. Through microscopy, we have seen the colocalization of EB1, one such protein, with atral microtubules during anaphase. Using microinjection in live cells, we can block the function of this protein and others and then study the effects this has on the onset of cytokinesis.