Chromatin configurational dynamics in live cells reveals insights into gene localization within nucleus

A key aspect of chromatin organization is the existence of chromosome territories, which largely confine each chromosome to its own region of the nucleus, leading to reduced inter-chromosomal contacts in comparison to intra-chromosomal contacts. This behavior stands in contrast to expectations from simple polymer models of chromatin, which predict mixing of different chromosomes. Here, we seek to discover whether, within an individual chromosome, particular chromatin locations are themselves confined to their own regions within the nucleus. To this end, we have created a library of Schizosachcromyces pombe strains in which sequential repeats of the lacO gene are inserted into the genome at different locations. Subsequent binding by LacI-GFP fusion proteins creates a differently-located GFP-labeled locus in each strain. These strains also include an mCherry-labeled spindle pole body (SPB) and nuclear membrane, allowing us to track the locations of each GFP-labeled locus relative to these nuclear landmarks via video microscopy. By then averaging the 3D positions of each labeled locus over population and over time, we can determine the positional distribution of each locus, relative to defined nuclear coordinates. We present data from ten different loci spaced more-or-less regularly across Chr II (4.5 Mb) of Schizosachromyces pombe, which reveal gene-specific tendencies to localize to particular nuclear regions, demonstrating that the territory concept applies not only to entire chromosomes, but also to chromatin regions within chromosomes. In addition, these results represent an important step towards understanding the large-scale coarse-grained configuration of the chromatin polymer in interphase Schizosachcromyces pombe.