Understanding how different condensin activities regulate mitotic chromosome folding in human cells

In human cells, the SMC complex condensin plays a significant and essential role in chromosome condensation, but there is conflicting data. Studies from other groups have suggested that the loop extruding activity of condensin is important for chromosome folding, but a study from my host lab suggested that loop extrusion (LE) alone is not able to package chromosomes. Using molecular biology experiments and polymer simulations they hypothesized that condensin has an additional bridging induced phase separation (BIPS) activity that is required for correct chromosome folding. In its absence, chromosomes are not fully compacted leading to chromosome instability.I will collaborate closely with polymer physicists in Edinburgh to interpret experimental data and to understand how different condensin activities are necessary for chromosome folding. Together, we expect to provide a new model of condensin molecular functions based on experiments in vivo analyzed together with simulations of mitotic chromosomes. Deviations between simulations and experiments will be used to identify gaps in our knowledge leading to new hypothesis generation.My aim is to investigate how different condensin activities (BIPS vs LE) regulate mitotic chromosome folding. To achieve this I have the following objectives:(i) Use an in silico model of condensin-mediated chromatin folding with diverse levels of LE and BIPS to develop models of chromosome folding and generate testable hypotheses and predictions.(ii) In human cells replace endogenous condensin components with already identified separation of function mutants to alter the balance between BIPS and LE activities and assess their role in chromosome folding.(iii) Explore how different mutations affect condensin binding and clustering on mitotic chromosomes using super-resolution microscopy.