Confinement plus Myosin-II suppression maximizes heritable loss of chromosomes, as revealed by live-cell ChReporters.

A cell's mechanical environment can have many effects, but whether it impacts a cell's DNA sequence has remained unclear. To investigate this, we developed a live-cell method to measure changes in chromosome numbers. We edited constitutive genes with GFP/RFP-tags on single alleles and discovered that cells that lose Chromosome-reporters (ChReporters) become non-fluorescent. We applied our new tools to confined mitosis and to inhibition of the putative tumor suppressor Myosin-II. We quantified compression of mitotic chromatin in vivo and demonstrated that similar compression in vitro resulted in cell death, but also rare and heritable ChReptorter loss. Myosin-II suppression rescued lethal multipolar divisions and maximized ChReporter loss in 3D-compression and 2D-confinement, but not in standard 2D-culture. ChReporter loss associated with chromosome mis-segregation, rather than just the number of divisions, and loss in vitro and in mice was selected against in subsequent 2D-cultures. Inhibition of the spindle assembly checkpoint (SAC) caused ChReporter loss in 2D, as expected, but not in 3D-compression, suggesting a SAC perturbation. Thus, confinement and myosin-II affect DNA sequence and mechano-evolution, and ChReporters enable diverse studies of viable genetic changes.