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Estrogen hormones are implicated in a majority of breast cancers and estrogen receptor alpha (ER), the main nuclear factor mediating estrogen signaling, orchestrates a complex molecular circuitry that is not yet fully elucidated. Here, we investigated genome-wide DNA methylation, histone acetylation and transcription after estradiol (E2) deprivation and re-stimulation to better characterize the ability of ER to coordinate gene regulation. We found that E2 deprivation mostly resulted in DNA hypermethylation and histone deacetylation in enhancers. Transcriptome analysis revealed that E2 deprivation leads to a global down-regulation in gene expression, and more specifically of TET2 demethylase that may be involved in the DNA hypermethylation following short-term E2 deprivation. Further enrichment analysis of transcription factor (TF) binding and motif occurrence highlights the importance of ER connection mainly with two partner TF families, AP-1 and FOX. Theseinteractions takeplace in the proximity of E2 deprivation-mediated differentially methylated and histone acetylated enhancers. Finally, while most deprivation-dependent epigenetic changes were reversed following E2 re-stimulation, DNA hypermethylation and H3K27 deacetylation at certain enhancers were partially retained. Overall, these results show that inactivation of ER mediates rapid and mostly reversible epigenetic changes at enhancers, and bring new insight into early events, which may ultimately lead to endocrine resistance. Institut National du Cancer (INCa, France, in part); European Commission (EC) Seventh Framework Programme (FP7) Translational Cancer Research (TRANSCAN) Framework; Fondation ARC pour la Recherche sur le Cancer (France) (to Z.H.); Fonds National de la Recherche, Luxembourg [10100060 to A.S.]; IARC Fellowship (Marie Curie actions – People – COFUND to N.F.J., in part); PoSTDoctoral Fellowship of the Basque Government; Swiss National Science Foundation (SNSF) (to L.V., V.Y., R.M.). Funding for open access charge: IARC regular budget

Unexpectedly, the molecular pathogenesis of expanded CAG/CTG diseases does not include changes in 3D chromatin conformation., Expanded CAG/CTG repeats underlie 13 neurological disorders, including myotonic dystrophy type 1 (DM1) and Huntington’s disease (HD). Upon expansion, disease loci acquire heterochromatic characteristics, which may provoke changes to chromatin conformation and thereby affect both gene expression and repeat instability. Here, we tested this hypothesis by performing 4C sequencing at the DMPK and HTT loci from DM1 and HD–derived cells. We find that allele sizes ranging from 15 to 1700 repeats displayed similar chromatin interaction profiles. This was true for both loci and for alleles with different DNA methylation levels and CTCF binding. Moreover, the ectopic insertion of an expanded CAG repeat tract did not change the conformation of the surrounding chromatin. We conclude that CAG/CTG repeat expansions are not enough to alter chromatin conformation in cis. Therefore, it is unlikely that changes in chromatin interactions drive repeat instability or changes in gene expression in these disorders.

Access of mammalian transcription factors (TFs) to regulatory regions, an essential event for transcription regulation, is hindered by chromatin compaction involving nucleosome wrapping, repressive histone modifications and DNA methylation. Moreover, methylation of TF binding sites (TBSs) affects TF binding affinity to these sites. Remarkably, a special class of TFs called pioneer transcription factors (PFs) can access nucleosomal DNA, leading to nucleosome remodelling and chromatin opening. However, whether PFs can bind to methylated sites and induce DNA demethylation is largely unknown.Here, we set up a highly parallelized approach to investigate PF ability to bind methylated DNA and induce demethylation. Our results indicate that the interdependence between DNA methylation and TF binding is more complex than previously thought, even within a select group of TFs that have a strong pioneering activity; while most PFs do not induce changes in DNA methylation at their binding sites, we identified PFs that can protect DNA from methylation and PFs that can induce DNA demethylation at methylated binding sites. We called the latter “super pioneer transcription factors” (SPFs), as they are seemingly able to overcome several types of repressive epigenetic marks. Importantly, while most SPFs induce TET-dependent active DNA demethylation, SOX2 binding leads to passive demethylation by inhibition of the maintenance methyltransferase DNMT1 during replication. This important finding suggests a novel mechanism allowing TFs to interfere with the epigenetic memory during DNA replication.

The genome size is, on average, significantly larger in eukaryotes than in prokaryotes. This, on one hand contributed to the acquisition of a number of advantages. On the other hand, it increased the complexity of regulation of the activity, maintenance, and inheritance of the genomic material. To deal with this complexity, eukaryotic organisms acquired new proteins, called histones that not only allow packaging and protecting the DNA into a higher-order structure called chromatin, but can also regulate the accessibility to and the activity of different parts of the genome. This regulatory function is directed by multiple chemical modifications that can take place on the histones. Here, we introduce the most common histone modifications, the machineries that deposit and remove them, their distribution in the genome, and their role in key cellular processes, with a focus on transcriptional regulation and DNA repair.