Fig. 3.

Two proposed mechanisms to change the nucleolus position from the nuclear periphery to the centre. The sphere represents the nucleus membrane, and each quartile represents one model of the nucleolus in the nuclear periphery (left) or in the centre (right). Upper quartiles represent the mechanism modelled by Di Stefano et al. [29], in which heterochromatin has strong repulsion against other chromatin domains and the nucleolus is modelled as thick beads of the chromatin fibre. The nucleolus localises at the periphery (left) and moves to the centre (right) only upon self-attraction of its beads. They emphasise the role of specific interaction forces. Bottom quartiles represent the mechanism modelled by Nooijer et al. [30], in which heterochromatin is modelled as big spheres, one for each chromatid representing the centromeres and the nucleolus is a single sphere, bigger than centromeres, attached to four chromatid arms. When the chromatid arms are modelled as linear polymers, possibly with loops, centromeres and the nucleolus localise at the nucleus centre. When the chromosomes are modelled in the rosette configuration, centromeres remain peripherical but apart from each other and from the nucleolus, which moves to the centre of the nucleus. They emphasise the role of entropy.