Fig. 4.

Conformations of chromatin loops and their repulsive effects. A) Low concentration of loops on a surface leads to a mushroom conformation of the loops. At high concentrations and with space restricted, loops adopt a brush conformation. B) Spheres with loops in a brush conformation repel each other due to steric hindrance, or osmotic repulsion, between the loops. C) We identify four possible mechanisms of forming chromatin polymer loops: 1) attraction between fixed monomers (specific loops); 2) a general self-attraction of all monomers; 3) loop extrusion by loop extruders (yellow), forming growing loops at any position, but modulated by the presence of other effectors (red) bound to the chromatin fibre; and 4) binding, mediated by proteins (blue) or intrinsic attraction, of monomers that spontaneously approach each other. D) Scheme of the interaction between centromeres (blue) of chromosomes in the Rabl configuration observed by [52]. When condensin II is present in mitotic chromosomes, the brush conformation of highly compacted chromatid arms repel the centromeres. And when condensin II is absent in mitotic chromosomes, the loose conformation of chromatid arms allow attraction of centromeres.