Large-scale manipulation of radial positioning does not affect most aspects of genome organization
Although the spatial organization of the genome is closely linked to biological function, genome structure is highly stochastic. Within this heterogeneity, specific function-associated structural elements must be maintained, even when the nucleus is deformed due to physiological physical constraints. The radial positioning of genomic loci - their distance from the nuclear periphery - has long been considered an important feature of genome organization which is correlated with both structural elements and genomic activity. In the current study, we developed an experimental system for manipulating the radial positioning of the genome, by expressing the sperm-specific protein Prm1 in somatic cells. By microscopy, we observe that initial Prm1 nuclear foci develop within 72 hours into a large Prm1 focus occupying most of the nuclear interior, while the entire genome is driven towards the nuclear periphery, resulting in a 3-5 fold reduction in the volume that the genome occupies. Noting that this system enables isolation of a pure population of cells with reorganized nuclei, we then used Hi-C to study the effects of this perturbation. Remarkably, we find that interaction patterns are largely robust to this major nuclear reorganization, with minor changes which mostly reflect a strengthening of heterochromatin self-interactions. Our experimental system provides means for manipulating nuclear organization in a reproducible manner, potentially allowing to examine radial positioning decoupled from other features of genome organization. Highlighting the complementary nature of microscopic and genomic methods, our work further suggests a remarkable resilience of genome structure such that large-scale nuclear changes, including chromosome compression and changes in radial positioning, can occur without extensive alteration of functional genome organization.