It was found that proteins promote the formation of mitotic spindles through phase transformation

On September 17, cell magazine published online the phase transitions of spindle associated protein regular spindle apparatuses assembly by Zhu Xueliang, Institute of Biochemistry and cell biology, Shanghai Institute of life sciences, Chinese Academy of Sciences, and Zheng Yixian, research group, Carnegie Institution, Washington, USA In this study, we found that the mitotic regulatory protein BugZ can undergo phase transformation under physiological conditions, resulting in a large number of BugZ molecules polymerizing to form a special structure Moreover, this phase transition plays an important role in promoting the assembly of mitotic spindles "Phase transition" as a property of matter (such as the transformation between water, ice and water vapor) has been widely known in the physical world for a long time, but the discovery of protein phase transition and its biological function in cells is still rare Mitosis is a process of equal chromosome separation during cell proliferation, which is very important to the genetic stability of life Spindles are the organelles responsible for chromosome separation, in which microtubules, the cytoskeleton formed by the aggregation of microtubule proteins, are responsible for binding and pulling chromatids Zheng Yixian and Zhu Xueliang's laboratories have been working together to explain the structure, properties and functions of the spindle matrix outside the spindle microtubules Recently, they have found that BugZ has made an important contribution to the efficiency and accuracy of mitosis In this study, their co directed postdoctoral researcher Jiang Hao and his research partners found that BugZ is rich in evolutionarily conservative low complexity domain Interestingly, through the hydrophobic interaction between molecules, BugZ can form a drop like structure with different sizes and be separated from aqueous solution The formation of droplets is reversible and requires appropriate temperature and concentration, which is consistent with the phase transition characteristics of substances Moreover, the droplets formed by BugZ can enrich microtubule proteins, promote microtubule polymerization, and make microtubules into bundles BugZ can also undergo phase transformation on microtubules, and the presence of microtubules can greatly reduce the concentration of BugZ required for phase transformation More importantly, the phase transformation of BugZ promotes the assembly of the spindle matrix and the formation of the spindle These findings provide new concepts and knowledge for the regulation mechanism of mitosis and open a new door for the research in this field The research is supported by funds from NSFC, Ministry of science and technology, Chinese Academy of Sciences and other institutions.