Plasticity of genome structure and organization governed by the differential activity of SMC complexes*

Understanding the role of SMC (Structural Maintenance of Chromosomes) complexes in organizing the genome has been a long-standing research avenue. Recent experiments studying chromosome architecture following the depletion of various SMC complexes have uncovered a number of phenotypic variants. Here, we adopt an energy-landscape-based polymer model of chromosomes that features SMC-driven linear compaction as an externally controllable degree of freedom. The linear compaction potential, also called the 'ideal chromosome', is further decomposed into short- and long-range components, associated with the activity of SMC variants like condensins and cohesin. As we modulate the relative intensity of short- versus long-range linear compaction, we find the emergence of structural phenotypes, such as chromosome territories and spatially clustered centromeres. These structural phenotypes highlight plasticity in the genome architecture that is directly associated with the differential activity of SMC variants. Our model helps rationalize both the SMC-depletion experiments, and aspects of genome architecture across the evolutionary tree featuring species lacking certain SMC variants.