Fig. 5. SER patches are dynamic and are rapidly reabsorbed into the ER polygonal meshwork upon removal of PDMP. (A) Live imaging by wide-field microscopy of PDMP-treated HeLa TetOff cells. Each row shows a different field of cells, imaged in the presence of PDMP. The arrow in the top row images indicates an SER patch that has fused with a smaller one at 30 seconds. After 6 minutes the patch has become less elongated and has changed position relative to the nuclear envelope. The arrow in the bottom row indicates a large patch, which appears to be undergoing fission at the end of the imaging period. See Movie 1 in supplementary material for an illustration of the genesis and dynamics of SER patches. (B) PDMP-treated cells were placed in PDMP-free medium and immediately subjected to time-lapse imaging by wide-field microscopy. A movie of this sequence is available in supplementary material Movie 3). In all panels, the numbers on the left indicate the time (in seconds) from the start of the imaging experiment. Bars, 10 µm.