Expanding Heterochromatin Reveals Discrete Subtelomeric Domains Delimited by Chromatin Landscape Transitions
bioRxiv preprint doi: https://doi.org/10.1101/187138; this version posted November 14, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. Expanding heterochromatin reveals discrete subtelomeric domains delimited by chromatin landscape transitions Antoine Hocher1,2, Myriam Ruault1,2, Petra Kaferle1,2, Marc Descrimes1,2, Mickael Garnier1,2, Antonin Morillon1,2, Angela Taddei1,2 Affiliations: 1 Institut Curie, PSL Research University, CNRS, UMR3664, F-75005 Paris, France 2 Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR3664, F-75005 Paris, France Abstract The eukaryotic genome is divided into chromosomal domains of heterochromatin and euchromatin. Transcriptionally silent heterochromatin is found at subtelomeric regions, leading to the telomeric position effect (TPE) in yeast, fly and man. Heterochromatin generally initiates and spreads from defined loci, and diverse mechanisms prevent the ectopic spread of heterochromatin into euchromatin. Here, we overexpressed the silencing factor Sir3 at various levels in yeast, and found that Sir3 spreading into Extended Silent Domains (ESD) eventually reached saturation at subtelomeres. We observed that Sir3 spreading into ESDs covered zone associated with specific histone marks in wild-type cells and stopped at zones of histone mark transitions including H3K79 tri-methylation levels. The conserved enzyme Dot1 deposits H3K79 methylation, and we found that it is essential for viability upon overexpression of Sir3, but not of a spreading-defective mutant Sir3A2Q. These data suggest that H3K79 methylation actively blocks Sir3 spreading. Lastly, our meta- analysis uncovers previously uncharacterized discrete subtelomeric domains associated with specific chromatin features offering a new viewpoint on how to separate subtelomeres from the core chromosome.
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