The Effect of Ionic Strength in Microtubule Tactoid Formation

Cell division via mitosis is one of the most important biological processes to sustain life. Microtubules, along with their associated proteins, crosslinkers, and enzymes, play a crucial role in the formation of the mitotic spindle. Previous studies on self-organization of microtubules showed that, in presence of polymer crowding agents, microtubules self-organize into bundles. Introducing certain concentrations of an antiparallel crosslinker, MAP65, in the system resulted in the bundles coalescing into homogenous, birefringent tactoids. Unlike the meiotic spindle and tactoids observed with actin filaments, which have been shown to have properties of liquid crystals, microtubule tactoids are solids. In an effort to investigate the mechanism of the organization and possibly alter the interactions to reduce the solidity of the tactoids, we altered the ionic strength of the buffer when forming tactoids in the presence of MAP65. We varied the concentrations of NaCl, KCl, and MgCl₂. The salt concentration affected the MT-MAP65 and MAP65-MAP65 bonds at different rates. Both of these interactions altered the formation of tactoids.