The deep invagination of the inner nuclear membrane into the nucleoplasm in the ascites hepatoma cells

Abstract

IT has b een well established that the nuclear envelope of the interphase cell, in animals and in some kinds of plants, is composed of two parallel membranes [l, 3, 121. Some morphological evidences suggesting the nuclear-cytoplasmic interrelationships have also been demonstrated in electron micrographs: the existence of continuities between the membranes of the nuclear envelope and those of the endoplasmic reticulum [4, 12, 131; of several types of discontinuities in the nuclear envelope 15, 131; of deep invaginations of double nuclear membranes into the nuclei, engulfing a portion of cytoplasmic materials [2, 71; of protrusions of the outer nuclear membrane [7, 121; of “bleb” formations of nuclei towards the cytoplasm [6, 91; and of annulate’lamellae [lo, 111. The interpretation that the nuclear membrane is another local differentiation of the endoplasmic reticulum was proposed by Watson [la, 131 and supported by Palade [8]. In the course of electron microscopic study of various ascites hepatomas of rats, the author has met the picture showing a new type of the invagination of nuclear membrane into the nucleoplasm, which has not hitherto been recorded. The present