Origin and Fate of Paired Cisternae in Mitotic Aortic Cells of Swine

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Abstract
Two hundred and sixty-six mitotic cells were ultrastructurally studied in the endothelium, intima and media of swine aorta after a repeated balloon denudation procedure. The structure and behavior of the mitotic apparatus were morphologically identical in all mitotic cells of these three layers. Paired cisternae were observed in all mitotic phases except interphase. In prophase the nuclear envelope was undulated and folded resulting in four-layered membranous structures. The inner membrane of the original nuclear envelope became the inner two layers of the four-layered structure which resembled the paired cisternae observed in the later mitotic stages. The paired cisternae which always consisted of four-layered membranes were distributed in the periphery of the mitotic apparatus and were not connected to the chromosomes during metaphase and anaphase. In early telophase, paired cisternae came into contact with the chromosomal surface and split into two separate double-layered membranes, spreading over the chromosomal mass. In mid-telophase, the paired cisternae were still connected to the poorly developed nucleus, around which the nuclear envelope had already formed. No paired cisternae were observed in the cells with well-developed nuclei in late telophase. It was concluded that the paired cisternae originated in the nuclear envelope and were later used to reconstruct the nuclear envelopes in the daughter cells.