Efficiency of NHEJ and HR altered by Pml NB disruption. (A) Efficiency of NHEJ-C (compatible DNA ends), NHEJ-I (incompatible DNA ends), and HR pathways in primary MEFs (n = 3). The efficiency of repair was measured by quantification of green fluorescent protein (GFP) fluorescence expression, which can only occur when linearized plasmids are accurately ligated (NHEJ-C) or repaired (NHEJ-I and HR). (B) Efficiency of NHEJ-C in lineage-depleted BM cells (n ≥ 5). (C) Efficiency of NHEJ-C, NHEJ-I, and HR in U937-Empty vector and U937-PR9 cell lines, 48 hours after ZnSO₄ treatment of induction of PML-RARα expression (n = 4). Western blot analysis of whole-cell lysates from U937-Empty vector and U937-PR9 cell lines treated with (+) or without (−) ZnSO₄ confirming PML-RARα expression. Tubulin was used as loading control. (A-C) Two-tailed unpaired Student t test analyses were performed. (D) Percentage of chromosomal aberrations (breaks, gaps, and rearrangements) in MEFs at the indicated time post-IR (n > 40 metaphase spreads from 3 independent experiments). Representative images (inset; original magnification ×100) of a chromatid rearrangement and a chromatid gap. (E) Sister chromatid exchange (SCE) rate per chromosome in MEFs, nontreated or treated with IR (n > 30 metaphase spreads from 3 independent experiments). Representative image (inset; original magnification ×100) of SCEs. (D-E) The 2-tailed Mann-Whitney U test was used.