The genesis of paired cisternae during the mitotic cycle.

Paired cisternae, which are conspicuous in mitotically active cells, are two or more flattened, membrane-bound saccules stacked in parallel arrays. The origin, development, and fate of paired cisternae during the cell cycle were studied in a poorly differentiated carcinoma of the eyelid. Early in the mitotic cycle, multiple membrane-bound, ovoid vesicles separated by interconnecting septa formed at the nuclear-cytoplasmic interface coincident with the disappearance of the nuclear envelope. These vesicles became progressively flattened and elongated to form paired cisternae, and by late prophase, had migrated to the cell periphery. During early anaphase, intimate association of paired cisternae with condensing chromosomes was observed. During late anaphase and telophase, distension of the cisternae resulted in vesicles similar to those observed in prophase cells. An apparent coalescence of these distended vesicles around the aggregated chromatin of daughter cells resulted in newly formed nuclear envelopes. Paired cisternae appear to be specialized nuclear membrane-derived structures that are fundamental in the generation of nuclear membranes of daughter cells. An infrequently observed variant of paired cisternae, subsurface confronting cisternae, is briefly described.