Rapid DNA replication origin licensing protects stem cell pluripotency
Abstract
Complete and robust human genome duplication requires loading MCM helicase complexes at many DNA replication origins, an essential process termed origin licensing. Licensing is restricted to G1 phase of the cell cycle, but G1 length varies widely among cell types. Using quantitative single cell analyses we found that pluripotent stem cells with naturally short G1 phases load MCM much faster than their isogenic differentiated counterparts with long G1 phases. During the earliest stages of differentiation towards all lineages, MCM loading slows concurrently with G1 lengthening, revealing developmental control of MCM loading. In contrast, ectopic Cyclin E overproduction uncouples short G1 from fast MCM loading. Rapid licensing in stem cells is caused by accumulation of the MCM loading protein, Cdt1. Prematurely slowing MCM loading in pluripotent cells not only lengthens G1 but also accelerates differentiation. Thus, rapid origin licensing is an intrinsic characteristic of stem cells that contributes to pluripotency maintenance.
Article and author information
Author details
Funding
National Institutes of Health (Research Grant GM074917)
- Anja-Katrin Bielinsky
National Science Foundation (Graduate Student Research Fellowship DGE1144081)
- Jacob Peter Matson
W. M. Keck Foundation (Research Grant)
- Jeremy E Purvis
- Jeanette Gowen Cook
National Institutes of Health (Training Grant T32CA009138)
- Ryan M Baxley
National Institutes of Health (Research Grant GM083024)
- Jeanette Gowen Cook
National Institutes of Health (Research Grant DP2HD091800)
- Jeremy E Purvis
National Institutes of Health (Research Grant GM102413)
- Jeanette Gowen Cook
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Bruce Stillman, Cold Spring Harbor Laboratory, United States
Version history
- Received: July 17, 2017
- Accepted: November 16, 2017
- Accepted Manuscript published: November 17, 2017 (version 1)
- Version of Record published: December 7, 2017 (version 2)
- Version of Record updated: June 5, 2019 (version 3)
Copyright
© 2017, Matson 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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- Cell Biology
- Chromosomes and Gene Expression
Histone H1 participates in chromatin condensation and regulates nuclear processes. Human somatic cells may contain up to seven histone H1 variants, although their functional heterogeneity is not fully understood. Here, we have profiled the differential nuclear distribution of the somatic H1 repertoire in human cells through imaging techniques including super-resolution microscopy. H1 variants exhibit characteristic distribution patterns in both interphase and mitosis. H1.2, H1.3, and H1.5 are universally enriched at the nuclear periphery in all cell lines analyzed and co-localize with compacted DNA. H1.0 shows a less pronounced peripheral localization, with apparent variability among different cell lines. On the other hand, H1.4 and H1X are distributed throughout the nucleus, being H1X universally enriched in high-GC regions and abundant in the nucleoli. Interestingly, H1.4 and H1.0 show a more peripheral distribution in cell lines lacking H1.3 and H1.5. The differential distribution patterns of H1 suggest specific functionalities in organizing lamina-associated domains or nucleolar activity, which is further supported by a distinct response of H1X or phosphorylated H1.4 to the inhibition of ribosomal DNA transcription. Moreover, H1 variants depletion affects chromatin structure in a variant-specific manner. Concretely, H1.2 knock-down, either alone or combined, triggers a global chromatin decompaction. Overall, imaging has allowed us to distinguish H1 variants distribution beyond the segregation in two groups denoted by previous ChIP-Seq determinations. Our results support H1 variants heterogeneity and suggest that variant-specific functionality can be shared between different cell types.