Cell cycle-dependent changes in non-membranous nuclear ghosts from HeLa cells.

Abstract

ABSTRACT Non-membranous nuclear ghosts are isolated from the nuclei of cultured HeLa cells after successive treatments with detergents and high ionic strength (0·5 M MgCl2) buffers. These ghosts have been shown by Keller & Riley to consist of a network consisting of annuli (90 nm in diameter), rod-like structures and dense bodies interconnected by DNase-sensitive strands. In nuclear ghosts purified from HeLa cells synchronized by a double thymidine block technique, the arrangement of these components exhibits dramatic cell cycle-dependent organizational differences. During G1 the small dense bodies (or aggregates) are widely dispersed and appear to be associated with the surface of the ghost. In S-phase, only a single (large) dense body is present and it is located in the centre of the ghost. The appearance of nuclear ghosts from cells in G2 is intermediate between those observed in G1 and S. These cell cycle-dependent organizational differences in the ultrastructure of nuclear ghosts are paralleled by differences in their susceptibility in suspension to DNase I. The G1 -phase ghost is markedly sensitive, whereas the S-phase ghost has both a sensitive component, the network consisting of annuli and rod-like structures connected by thin strands, and a resistant component, the single (large) dense aggregate. The unique morphology of ghosts at a particular phase of the cell cycle and the similarity of the polypeptide species present in ghosts isolated at these 3 phases of the cell cycle lead us to conclude that the various organizational patterns described are alternative cell cycle-dependent configurations of what is fundamentally the same macromolecular complex. A model is presented in which internal nuclear skeletal components and the non-membranous nuclear envelope are considered to be dynamic interacting components of interphase nuclei. This model provides a physiological rationale for nuclear envelope expansion capability which has been observed under experimental conditions by many investigators.