Interphase Chromatin Dynamics in Response to Double Stranded DNA Breaks

Abstract

The dynamic organization of chromatin inside the eukaryotic cell nucleus is essential to the regulation of the genome such as maintaining its integrity, gene expression and replication. However, the physical picture of chromatin structure and dynamics remains unclear and requires identifying the dynamical and structural signatures of specific biological processes. In this work, we study the chromatin dynamics in interphase, time between two cell divisions, in response to DNA damage. As shown previously, chromatin dynamics across the whole nucleus change dramatically after DNA damage; chromatin's coherent motion is eliminated, while its local mobility increases and its compaction decreases [1]. Here, we explore the local chromatin dynamics and compaction in response to local DNA damage in human cells. To do so, we induce double stranded DNA breaks (DSBs), which we visualize using 53BP1-mCherry, and observe the spatiotemporal evolution of their dynamics using single particle tracking. Simultaneously, we use histone H2B-GFP as a reporter on the chromatin compaction, to compare DSB dynamics inside the heterochromatin and euchromatin. To elucidate the dynamic signature of the local DNA damage response, we vary the number of DSBs as well as explore the ATP-dependence of these processes. Our preliminary results show that with an increasing DSB count the local subdiffusive dynamics of the DSBs remains unchanged. We also explore the relationship between the protein aggregation, diffusion coefficient and chromatin compaction at a DSB. [1] Zidovska A, Weitz DA, Mitchison TJ, Proc. Natl. Acad. Sci. USA, 110(39), 1555560, 2013.