DNMT3b Dysfunction Promotes DNA cleavages at Centromeric R-loops to Increase Centromere Instability

ABSTRACTThis study investigates how DNA methyltransferase 3b (DNMT3b) dysfunction causes genome instability. We showed that in DNMT3b deficient cells, R-loops contribute to prominent γH2AX signal, which was mapped to repetitive satellite sequences including centromere regions. By ChIP and DRIP analyses, our data revealed that centromeric R-loops in DNMT3b deficient cells are removed by XPG/XPF, thus generating DNA breaks in centromeres to increase mitotic aberration. In immunodeficiency-centromeric instability-facial anomalies (ICF) patient cells carrying the loss-of-function mutation at DNMT3b, knockdown of XPG/XPF in ICF cells also reduces DNA breaks in centromere while bringing up centromeric R-loop to the level similar to that in wild-type cells. These results suggest that DNMT3b has a critical function in preventing XPG/XPF-mediated cleavages at centromeric R-loop sites. Finally, we showed the involvement of non-homologous end-joining repair at centromeric sites in ICF cells. Thus, DNA cleavages at centromeric R-loops with error-prone repair undermine centromere stability in ICF cells.

DNA damage induction in bone marrow cells of mice after farnesenes and 2,5-dimethylpyrazine sniffing

Background. Pheromones are an important regulatory link of synecological contacts in numerous animal species. Chemo-signaling participates in establishing of population social structure, it regulates different types of behavior, changes hormonal state and maturation rate, etc. It also can affect the genetic material expression and integrity. Material and methods. Groups of adult males of CBA/Lac/Sto/Rap strain were exposed to volatile chemosignals (mixture of α- and β-farnesenes or 2,5-dime thylpyrazine) for 2 or 24 hours. Bone marrow cells were prepared for single cell gel electrophoresis (comet assay test). Content of DNA in comet cells were analyzed. In case of 24 hours exposure bone marrow cells were fixed also for ana-telophase analysis. Results. It is shown that exposures with farnesenes or 2,5-DMP both damage genetic material of bone marrow cells. It also followed by induction of mitotic aberration frequency. Simultaneous exposure with all chemosignals does not increase damaging effect. Conclusion. Chemosignals which serve as stress-pheromones in mice decrease also the integrity of genetic material in bone marrow cells of recipients. It could be a mechanism of pheromonal impact on density and space-genetic structure of mouse populations.