Local barrier dynamics can shape whole-chromosome morphology. (A) Heat map indicating vermicelli conformation at various barrier bound times τb relative to extruder lifetime (τE) at fixed barrier occupancy (0.7). The red dashed line indicates parameter sets displaying prominent vermicelli (scores above 0.65). Left column: representative conformation above simulated microscopy for chromatin (blue) and extruders (purple) at sevenfold increased extruder lifetime approximating WAPL depletion and very short barrier bound time (τb ≪ τE), position in heat map indicated by (i). Right column: Similarly, albeit for very long barrier bound time (τb ≫ τE), with position in heat map indicated by (ii). (B) Illustration of how dynamic barriers can have global consequences for vermicelli formation by enabling gap closure between consecutive loops. In this three-step process, an extruder is halted at a barrier next to a gap; the barrier unbinds, allowing extruder bypass; finally, the gap can be closed, irrespective of whether the barrier rebinds.
