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The N-terminal domain of TET1 promotes the formation of dense chromatin regions refractory to transcription

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Abstract

TET (ten-eleven translocation) enzymes initiate active cytosine demethylation via the oxidation of 5-methylcytosine. TET1 is composed of a C-terminal domain, which bears the catalytic activity of the enzyme, and a N-terminal region that is less well characterized except for the CXXC domain responsible for the targeting to CpG islands. While cytosine demethylation induced by TET1 promotes transcription, this protein also interacts with chromatin-regulating factors that rather silence this process, the coordination between these two opposite functions of TET1 being unclear. In the present work, we uncover a new function of the N-terminal part of the TET1 protein in the regulation of the chromatin architecture. This domain of the protein promotes the establishment of a compact chromatin architecture displaying reduced exchange rate of core histones and partial dissociation of the histone linker. This chromatin reorganization process, which does not rely on the CXXC domain, is associated with a global shutdown of transcription and an increase in heterochromatin-associated histone epigenetic marks. Based on these findings, we propose that the dense chromatin organization generated by the N-terminal domain of TET1 could contribute to restraining the transcription enhancement induced by the DNA demethylation activity of this enzyme.

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The raw datasets used during the current study are available from the corresponding authors on reasonable request.

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Acknowledgements

We thank the engineers of the Microscopy Rennes Imaging Center (BIOSIT, Université Rennes 1), Stéphanie Dutertre and Xavier Pinson for technical help on the microscopes. We are also grateful to the engineers of the flow cytometry facility (BIOSIT, Université Rennes 1), Laurent Deleurme and Alexis Aimé for technical assistance. This work would not have been possible without the generous donation of plasmids from Heinrich Leonhardt, Cristina Cardoso, Wei Xie, Haico Van Attikum, Gyula Timinszky, and Jan Ellenberg.

Funding

This work was funded by the Ligue contre le Cancer du Grand-Ouest, the Conseil Régional de Bretagne and the Institut Universitaire de France. The Microscopy-Rennes Imaging Center (BIOSIT, Université Rennes 1), is a member of the national infrastructure France-BioImaging supported by the French National Research Agency (ANR-10-INBS-04).

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A.L., S.Z., S.H., and R.S. completed the experiments within the manuscript. C.C. generated cell lines and DNA constructs. A.L., S.Z., S.H., and O.D.A. performed data analysis. G.S. and S.H. conceived and supervised this study. S.H. wrote the manuscript. All authors read and commented on the manuscript.

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Correspondence to Gilles Salbert or Sébastien Huet.

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The authors declare no competing interests.

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Supplementary Figure 1

. Controls of the changes in chromatin compaction state upon expression of unfused GFP and GFP-TET1. a. Images of U2OS cells stained with Hoechst as well as an anti-dsDNA antibody, and expressing either unfused GFP (GFP) or full-length (GFPTET1). Cells were fixed and stained 24 h after transfection. More than 30 cells were imaged per condition and a typical image is shown for each. b. Timelapse image sequence of live U2OS cells stably expressing H2B-mCherry and transiently expressing unfused GFP. The images were pseudocolored according to the look-up table displayed below the images. The timelapse acquisition started 6 h after transfection c. Images from a. were quantified to monitor the changes in GFP expression levels (black curve), assessed by GFP fluorescence intensity, in parallel to the chromatin spatial distribution, assessed by the fluorescence contrast estimated from the images of the H2B-mCherry signal (red curve). The curves show a mean ± SD of 11 cells. Before averaging, the individual curves for the chromatin contrast and the expression level were aligned in time using as a reference the timepoint at which the normalized expression level equalled 0.5. The time was then estimated relative to this reference timepoint. For panels a. and b., scale bars = 10 μm

Supplementary Figure 2. Influence of the N-terminal and C-terminal domains of TET1 on the levels of 5-hmC and the chromatin patterns. a. Images of Hoechst-stained UO2S cells expressing either unfused GFP, full-length TET1 (GFP-FL), the C-terminal domain of TET1 (CTER-GFP) or the N-terminal domain of TET1 (NTER-GFP), all tagged with GFP. The cells were also immunostained for 5-hmC. Cells were fixed and stained 24 h after transfection. More than 30 cells were imaged per condition and a typical image is shown for each. Scale bars = 10 μm. b. Scatter plot of the mean nuclear intensity of the 5hmC staining plotted as a function of the mean nuclear signal in the GFP channel measured from the cells shown in a. c. Scatter plot of the fluorescence contrast, estimated from the Hoechst staining, plotted against the mean nuclear GFP signal measured from the images of U2OS cells expressing GFP-tagged full-length or the N-terminal domain of TET1, which are shown on figure 2b. The correlation between the contrast and the GFP signal was estimated by calculating the Spearman coefficient. The dotted line correponds to the linear fit of the experimental points. d. The colocalisation between the Hoechst and GFP stainings in U2OS cells expressing GFP-tagged full-length or the N-terminal domain of TET1 was estimated by calculating the Pearson coefficient between the two channels on the images shown on figure 2a

Supplementary Figure 3. Analysis of EU and H3K27me3 staining in cells expressing fulllength or the N-terminal domain of TET1. a. The colocalization between the Hoechst and EU staining on the images shown on figure 4a was estimated by calculating the Pearson coefficient between the two channels b. Gating strategy for the analysis of EU and H3K27me3 staining by flow cytometry. The first gate was performed on the scatter plot of SSC-A against FSC-A to select living cells (right). The second gate was applied to the scatter plot of SSC-A against SSC-H to remove cell doublets (middle). Finally, the scatter plot of the EU or H3K27me3 signals against the GFP signal (FITC-A::GFP) was analyzed (left). Gates for cells negative for GFP (GFP-) or negative for EU or H3K27me3 staining were established based on the signals obtained for U2OS cells that were not subjected to transfection and EU or H3K27me3 staining. Finally, the GFP positive cells (PDF 1796 KB)

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Lejart, A., Zentout, S., Chapuis, C. et al. The N-terminal domain of TET1 promotes the formation of dense chromatin regions refractory to transcription. Chromosoma 131, 47–58 (2022). https://doi.org/10.1007/s00412-022-00769-0

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  • DOI: https://doi.org/10.1007/s00412-022-00769-0

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