Gene expression profiles with WT and Tet KO osteoblasts

The Ten-eleven translocation (TET) family of dioxygenases can mediate cytosine demethylation by catalyzing the oxidation of 5-methylcytosine (5mC). TET-mediated DNA demethylation controls the proper differentiation of embryonic stem cells and TET proteins display functional redundancy during early gastrulation. However, it is unclear if TET proteins have functional significance in mammalian skeletal development. Here, we report that Tet deficiency in mesoderm mesenchymal stem cells results in severe defects of bone development. The existence of any single Tet gene allele can support early bone formation, suggesting a potential functional redundancy of TET proteins. Integrative analyses of RNA-seq, Whole Genome Bisulfite Sequencing (WGBS) and Assay for Transposase-Accessible Chromatin (ATAC-seq) demonstrate that TET-mediated demethylation increases the chromatin accessibility of target genes by RUNX2 and facilities RUNX2-regulated transcription. In addition, TET proteins interact with RUNX2 through their catalytic domain to regulate cytosine methylation around RUNX2 binding region. The catalytic domain is indispensable for TET proteins to regulate RUNX2 transcription activity on its target genes and to regulate bone development. These results demonstrate that TET proteins function redundantly to regulate RUNX2 activity via dual mechanisms and maintain skeletal homeostasis. Overall design: Gene expression profiles with WT and Tet KO osteoblasts, three repeats.