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iScience. 2018 Jun 29;4:216-235. doi: 10.1016/j.isci.2018.06.001. Epub 2018 Jun 5.

Live-Cell Imaging of Chromatin Condensation Dynamics by CRISPR.

Xue Y1,2, Acar M1,2,3,4.

Author information

1
Department of Molecular Cellular and Developmental Biology, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA.
2
Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA.
3
Department of Physics, Yale University, 217 Prospect Street, New Haven, CT 06511, USA.
4
Lead Contact.

Abstract

The spatiotemporal organization of chromatin plays central roles in cellular function. The ribosomal DNA (rDNA) chromatin undergoes dynamic structural changes during mitosis and stress. Here, we developed a CRISPR-based imaging system and tracked the condensation dynamics of rDNA chromatin in live yeast cells under glucose starvation. We found that acute glucose starvation triggers rapid condensation of rDNA. Time-lapse microscopy revealed two stages for rDNA condensation: a "primary stage," when relaxed rDNA chromatin forms higher order loops or rings, and a "secondary stage," wehen the rDNA rings further condense into compact clusters. Twisting of rDNA rings accompanies the secondary stage. The condensin complex, but not the cohesin complex, is required for efficient rDNA condensation in response to glucose starvation. Furthermore, we found that the DNA helicase Sgs1 is essential for the survival of cells expressing rDNA-bound dCas9, suggesting a role for helicases in facilitating DNA replication at dCas9-binding sites.

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