Fig. 1. Metazoan cells undergo open mitosis. U2OS cells were transfected with a construct encoding the first 65 aa of Sec61 conjugated to (GFP-Sec61) and H2BtdTomato, and imaged in real time using spinning disk confocal microscopy throughout mitosis. Following chromatin condensation (prophase) the NE is torn apart and absorbed into the ER (pro-metaphase). When the chromosomes align on the metaphase plate there is little or no contact between chromosomes and the membranes of the ER (metaphase). The tubule tips of the ER first contact the chromatin during chromosome segregation (anaphase). The NE is reformed during cytokenisis (daughter cells). Scale bar, 10 µm.