R-loop and DNA damage accumulation lead to BM failure in cDKO mice. (A) Representative image of immunostaining of R-loop (green), γH2AX (red), and nuclei (blue, DAPI staining) on BM sections on day 4 after 4 mg of TAM. Images were acquired at ×20 magnification (first and third panels) and zoomed in ×5 for indicated areas. (B-C) Ratio of BM cells with positive R-loop (B) and γH2AX (C) during the 4-day time course after cDKO. For each experiment, 4 sections from 4 individual mice were analyzed at 5 time points. Statistical analysis represents t test. (D) Proposed model of genomic instability in cDKO cells. cDKO induces R-loop, replication stress, and DSB accumulation, cytosolic ssDNA with consequent activation of IFN, p53 and DDR pathways, and apoptotic cell death, hence disruption of stem cell homeostasis. See also supplemental Figure 7. ***P < .001.