The "paired cisternae" in mitotic cells of the pigeon esophageal epithelium.

Abstract

In the mitotic cells, from prometaphase to telophase, in the pigeon esophageal epithelium, straight or twisted profiles of four-layered membranous structure were observed which, corresponding to the so-called paired cisternae, was composed of two smooth inner membranes closely apposed in parallel with a narrow, moderately electron opaque space and two outer membranes studded with sparse ribosomes. Each of the inner membranes was continuous with the homolateral outer membranes at both ends of the profiles. Duplications of an inner membrane pair occurred sometimes.The paired cisternae presumably were formed at prometaphase by “stacking” or “folding over” of the remnants of the broken down nuclear envelope. At late anaphase to telophase the envelope of daughter nuclei seemed to be reconstituted, besides by the usual double membranes, partially by the paired cisternae. The paired cisternae split between the inner double membrane to cover the surface of the chromosomal mass. Thus, each of the inner membranes seemed to form the inner leaflet of the nuclear envelope and each of the rough-surfaced outer membranes its outer leaflet. At telophase after the completion of the envelope of the daughter nucleus, the paired cisternae still occurred occasionally without showing any connection with the nuclear envelope. Their further fate was unknown. In the interphase cells no paired cisternae were found.