Structural elements common to mitosis and apoptosis

Both mitotic and apoptotic cells display hypercondensation of the chromatin and loss of the nuclear envelope (Lazebnik et at., 1993). Herein, we descr ibe a third similarity between the two processes. We have observed, initial ly in apoptotic cells of the PC-12 lineage clusters of 40-60 (similar to 50 ) nm vesicles adjoined by a minor contingent of tubule vesicular elements o f 100-200 nm which are indistinguishable from their vesicular counterparts in mitotic PC-12 cells. The clusters of similar to 50 nm vesicles were subs equently observed in all studied rat tissue cells in apoptosis (plasma cell s and macrophages, secretory epithelial cells from pancreatic acini, ventra l lobe of prostate and mammary gland). Clusters of similar to 50 nm vesicle s comparable to those of the PC-12 cells were found in HeLa cells treated w ith human alfa TNF, in WEHI-3 cells exposed to VM 26 (a teneposide) (Sesso et at., 1997) and in HL-60 cells treated with thapsigargin, PC-12 and HeLa cells affixed to coverslips were double labelled and examined with the fluo rescence microscope to reveal simultaneously the disposition of the chromat in with Hoechst stain and the distribution of the fluorescence of Golgi or of Golgi-associated proteins. A common pattern of fluorescence was observed in a minor proportion of apoptotic cells using three different antibodies used. The label frequently appeared as finely dispersed granules in the cyt oplasm. In some apoptotic cells, relatively coarse granules were observed. This pattern of label distribution is compatible with the disposition of ve sicular clusters we have encountered in apoptotic PC-12 cells sectioned ser ially or semi serially. In such sections of both mitotic and apoptotic PC-1 2 cells, we noticed that the conglomerates of 50 nm vesicles were frequentl y associated with cisternae of the rough ER. Vesicles of similar size were also noted pinching off from the extremities of Golgi cisternae reduced in size, These cisternae diminish in length and width when they are in the pro cess of disassembling at the very beginning of mitosis and in apoptosis.