Assembly of Microtubule Tactoids Through Condensates of PRC1 Constructs

The cytoskeleton fulfills many essential roles that are necessary for cell function. Perhaps the most important of these roles is the formation of the mitotic spindle. The mitotic spindle is a complex and dynamic structure made up mainly of microtubules and numerous microtubule-associated proteins (MAPs), but the mechanisms behind its creation and regulation are not fully characterized. Recent research has focused on the link between liquid-liquid phase separation (LLPS) of MAPs and these microtubule organizations. Here, we focus on the protein regulator of cytokinesis 1 (PRC1), a spindle midzone-associated anti-parallel microtubule crosslinker. PRC1 is known to undergo LLPS to form condensed droplets without the need for additional crowders. Using confocal fluorescence microscopy and different constructs of PRC1, we investigate the ability of PRC1's structural domains to form droplets and hierarchically organize microtubule tactoids. We find that the removal of PRC1's unstructured C-terminal tail does not inhibit its ability to form droplets or microtubule tactoids in vitro. Removing part of PRC1's N-terminal rod domain inhibits but does not completely suppress droplet formation.