Shape study of Spindle-like microtubule tactoids using experiment and computation

Mitotic spindles during metaphase are a fundamentally important puzzle of biophysics at the base of the question of how a cell divides its genetic material. Mitotic spindle self-assembly is inherently non-equilibrium with a vast parameter space. Factors that play a role as a system include microtubules, molecular motors, crosslinkers, and associated proteins, whose working principles are not yet clear. Recently, we reconstituted a minimal model system for creating microtubule-based spindle-like assemblies using microtubules and the plant-derived crosslinker, MAP65. Here we have extended our work to determine the important requirements for tactoid formation by exploring different crowders or viscosity agents to show that they do not play a significant role determining the formation or shape of the tactoids. Also, using a computational approach we have shown that similar steady state tactoids can evolve from growing filaments that follow a damped Langevin equation and Hookean type crosslinkers. We explored the phase space of this organization by varying initial conditions like filament number, orientation, and length as well as crosslinker number, binding dynamics. Using these two directions we are uncovering the principles behind spindle organization using tactoid as a model.