Quantification of Interphase Chromatin Dynamics in Fission Yeast

In mammals and other higher organisms, interphase chromosomes remain separated from each other and compartmentalized into chromosome territories. In yeast, chromosomes adopt a Rabl configuration, with arms extending from centromeres tethered at the spindle pole body(SPB), functionally equivalent to the centrosome, to telomeres at the opposite nuclear envelope. These organizations generally constrain chromatin motion, and contribute to gene positioning inside the nucleus. On the other hand, active genes escape from such physical constraints and are located at active regions such as transcription factories and nuclear pore complexes(NPCs). In spite of extensive studies for these phenomena, how gene loci sustain and change their positioning during the cell cycle still remains unclear. In order to elucidate chromatin dynamics during interphase, we visualized several gene loci and the centromeres (and the SPB) on the fission yeast S. pombe chromosomes that show a Rabl configuration, and then tracked the positions of the loci on a longer time scale than conventional one. The statistical analysis of the physical distance from the SPB to each locus suggested that the gene loci show not only restricted diffusion due to the physical constraint of the Rabl configuration, but also a novel dynamic property, that is quite different from simple diffusive behaviors reported so far. In this presentation, we will discuss functional roles that such chromatin dynamics possibly play within the interphase nucleus.