C6wt and C6ko MEFs were seeded at 2500 cells per well into 96well plates. N = 3 for each treatment. The following day, cells were treated with camptothecin (5 mM final) for 16 hours. Post stress, cells were washed in PBS, fixed in 4% formaldehyde (EMS)/PBS for 60 minutes at 4C, washed with PBS, and permeabilized with 0.3% Triton-X 100/PBS. Primary antibody to mouse cleaved lamin A (Cell Signaling Technology) was added at 1:100, in normal goat serum, and incubated at 4C overnight. Plates were washed twice in PBS before adding secondary antibodies, AlexaFluor 488 anti-mouse IgG (Invitrogen), each at 1:800 in normal goat serum, and DNA staining dye, Hoechst 33342 (Invitrogen), at 1:10000, for 90 minutes at room temperature. Plates were washed again twice and left in PBS.