Live-cell imaging of marked chromosome regions reveals dynamics of mitotic chromosome resolution and compaction

Abstract

SummaryWhen human cells enter mitosis, chromosomes undergo substantial changes in their organization -sister chromatids are resolved and chromosomes are compacted.However we still do not fully comprehend the timing and coordination of these events. To address these, we need to evaluate both sister chromatid resolution and chromosome compaction in one assay. Here we analysed the change in configuration of marked chromosome regions over time, with high spatial and temporal resolution by live-cell imaging to judge sister resolution and compaction.This assay showed that sister chromatid resolution already begins in late G2 phase and completes in prophase after multiple attempts. Cohesins and WAPL antagonistically regulate sister chromatid resolution in late G2 and prophase whilst local enrichment of cohesin on chromosomes prevents precocious sister chromatid resolution. Moreover, the assay allowed quantitative evaluation of the timing and efficiency of condensin II and I activities in promoting sister chromatid resolution and chromosome compaction, respectively. Our real-time assay sheds new light on the dynamics of mitotic chromosome resolution and compaction.