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

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.