Fig. 2. Tracking untransfected and transfected cells over a number of cell divisions. To establish the extent of the lag caused by EGFP-emerin mutant (Del236-241), COS-7 cells transfected with EGFP-emerin constructs were monitored over four cell divisions using a fluorescent cell-tracking dye (PKH26). The fluorescent cell-tracking dye was incorporated into cell membranes at time 0, and its intensity examined at three time points 0, 56 and 104 hours. For the untransfected populations (wt, black dotted line; D236 (D236-241), blue dotted line; S54F, light-grey dotted line; 1-220, dark-grey dotted line), the fluorescence dye intensity decreases exponentially as the dye is dispersed between the daughter cells during cell division. Thus, the medium fluorescent intensity of PKH26 over time allows the cell-cycle timing to be monitored. Cells transfected with wild-type EGFP-emerin (black solid line) or mutants; missense S54F (light-grey solid line) and 1-220 (dark-grey solid line) showed the normal exponential decrease in dye intensity, whereas cells transfected with EGFP-emerin mutant Del236-241 (D236, blue solid line) show a steady decrease in dye intensity, meaning that these cells took longer to cycle.