Figure 1. UV/cold shock induces nuclear membrane bubbling.

(A) COS7 cells, with or without expressing EGFP, were exposed to UV irradiation at 480 mJoule/cm² and then incubated at 4°C for 5 minutes, prior to imaging by time-lapse microscopy at room temperature. Bubble formation (big red and small yellow arrows) from the nucleus is shown. Nuclear EGFP leaked into the gas bubble. See the enlarged pictures are at Supplementary Figure S1 for better resolution. (B) Under similar conditions, COS7 cells were exposed to UV irradiation (480 mJoule/cm²) and then cold shock (4°C for 5 min). The cells were then cultured at 4°C and 37°C, respectively, for indicated times. The extent of bubbling was counted. (C, D) Similarly, COS7 and B16F10 cells were exposed to UV (480 mJoule/cm²) /cold shock (4°C for 5 min) and then incubated at indicated temperatures for 0.5–4 hr. Internucleosomal DNA fragmentation was determined by agarose gel electrophoresis. (E) UV irradiation/cold shock-induced apoptosis is switched to bubbling cell death at low temperature, and vice versa.