Evidence for DNA-mediated nuclear compartmentalization distinct from phase separation
Abstract
RNA Polymerase II (Pol II) and transcription factors form concentrated hubs in cells via multivalent protein-protein interactions, often mediated by proteins with intrinsically disordered regions. During Herpes Simplex Virus infection, viral replication compartments (RCs) efficiently enrich host Pol II into membraneless domains, reminiscent of liquid-liquid phase-separation. Despite sharing several properties with phase-separated condensates, we show that RCs operate via a distinct mechanism wherein unrestricted nonspecific protein-DNA interactions efficiently outcompete host chromatin, profoundly influencing the way DNA binding proteins explore RCs. We find that the viral genome remains largely nucleosome-free, and this increase in accessibility allows Pol II and other DNA-binding proteins to repeatedly visit nearby DNA binding sites. This anisotropic behavior creates local accumulations of protein factors despite their unrestricted diffusion across RC boundaries. Our results reveal underappreciated consequences of nonspecific DNA binding in shaping gene activity, and suggest additional roles for chromatin in modulating nuclear function and organization.
Data availability
The GEO accession number for the ATAC-seq data is: GSE117335. The SPT trajectory data are available via Zenodo at DOI:10.5281/zenodo.1313872. The software used to generate these data is available at https://gitlab.com/tjian-darzacq-lab.
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Relative accessability of HSV1 genomic DNA compared with its host cell (ATAC-seq)NCBI Gene Expression Omnibus, GSE117335.
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Single Particle Tracking data for U2OS cells after infectionZenodo, 10.5281/zenodo.1313872.
Article and author information
Author details
Funding
National Institutes of Health (UO1- 497 EB021236)
- David Trombley McSwiggen
- Anders S Hansen
- Yvonne Hao
- Alec Basil Heckert
- Kayla K Umemoto
- Claire Dugast-Darzacq
- Xavier Darzacq
National Institutes of Health (U54-DK107980)
- David Trombley McSwiggen
- Anders S Hansen
- Yvonne Hao
- Alec Basil Heckert
- Kayla K Umemoto
- Claire Dugast-Darzacq
- Xavier Darzacq
California Institute for Regenerative Medicine (LA1-08013)
- Anders S Hansen
- Alec Basil Heckert
- Xavier Darzacq
Howard Hughes Medical Institute (003061)
- David Trombley McSwiggen
- Anders S Hansen
- Sheila S Teves
- Yvonne Hao
- Alec Basil Heckert
- Kayla K Umemoto
- Robert Tjian
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Jessica K Tyler, Weill Cornell Medicine, United States
Version history
- Received: March 26, 2019
- Accepted: April 29, 2019
- Accepted Manuscript published: April 30, 2019 (version 1)
- Accepted Manuscript updated: May 7, 2019 (version 2)
- Version of Record published: May 16, 2019 (version 3)
Copyright
© 2019, McSwiggen et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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The cohesin complex plays essential roles in chromosome segregation, 3D genome organisation, and DNA damage repair through its ability to modify DNA topology. In higher eukaryotes, meiotic chromosome function, and therefore fertility, requires cohesin complexes containing meiosis-specific kleisin subunits: REC8 and RAD21L in mammals and REC-8 and COH-3/4 in Caenorhabditis elegans. How these complexes perform the multiple functions of cohesin during meiosis and whether this involves different modes of DNA binding or dynamic association with chromosomes is poorly understood. Combining time-resolved methods of protein removal with live imaging and exploiting the temporospatial organisation of the C. elegans germline, we show that REC-8 complexes provide sister chromatid cohesion (SCC) and DNA repair, while COH-3/4 complexes control higher-order chromosome structure. High-abundance COH-3/4 complexes associate dynamically with individual chromatids in a manner dependent on cohesin loading (SCC-2) and removal (WAPL-1) factors. In contrast, low-abundance REC-8 complexes associate stably with chromosomes, tethering sister chromatids from S-phase until the meiotic divisions. Our results reveal that kleisin identity determines the function of meiotic cohesin by controlling the mode and regulation of cohesin–DNA association, and are consistent with a model in which SCC and DNA looping are performed by variant cohesin complexes that coexist on chromosomes.
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- Chromosomes and Gene Expression
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Though long non-coding RNAs (lncRNAs) represent a substantial fraction of the Pol II transcripts in multicellular animals, only a few have known functions. Here we report that the blocking activity of the Bithorax complex (BX-C) Fub-1 boundary is segmentally regulated by its own lncRNA. The Fub-1 boundary is located between the Ultrabithorax (Ubx) gene and the bxd/pbx regulatory domain, which is responsible for regulating Ubx expression in parasegment PS6/segment A1. Fub-1 consists of two hypersensitive sites, HS1 and HS2. HS1 is an insulator while HS2 functions primarily as an lncRNA promoter. To activate Ubx expression in PS6/A1, enhancers in the bxd/pbx domain must be able to bypass Fub-1 blocking activity. We show that the expression of the Fub-1 lncRNAs in PS6/A1 from the HS2 promoter inactivates Fub-1 insulating activity. Inactivation is due to read-through as the HS2 promoter must be directed toward HS1 to disrupt blocking.