Can microtubule diffusiophoresis be present during spindle formation?

Microtubules (MT) form the mitotic spindle assembly during mitosis in eukaryotic cells, and a concentration gradient of the protein Ran (in its GTP bound form – RanGTP) plays an important role during this process. As microtubules are negatively charged and concentration gradients of various species are ubiquitous in cells, we asked whether diffusiophoresis of microtubules can be present in such an environment. In this study, we first demonstrate migration of MTs in BRB80 buffer (which contains PIPES, EGTA, and MgCl₂) under MgCl₂ gradients and quantify the diffusiophoretic behavior by comparing with a multi-ion model of diffusiophoresis and diffusioosmosis. Then, we further study the diffusiophoresis of MT under various concentration gradients of relevant biological solutes (ATP, GTP, and RanQ69L) and unravel diffusiophoresis in more complex chemical environments.