Mitosis and protein synthesis. 3. Organelle relocation during normal and colcemid-arrested M-phase in HeLa S-3 cells

Abstract

During M-phase, most organelles in HeLa S-3 cells are relocated in the 'cortex' or outer-zone of cytoplasm. Elements of the rough endoplasmic reticulum (rER) and polysome assemblies persist to varying degrees from cell to cell in this zone. Dilatation of rER cisternae becomes prominent in a small percentage of metaphases, and its occurrence and significance is discussed. Remnants of the Golgi apparatus are almost invariably peripheralized. Its cisternal elements are lost in early mitosis, and reappear in late telophase. The inner zone of the protoplasm around the chromosomes loses its associated intermediate filaments and excludes organelles until cytokinesis commences. A rapid repopulation occurs by mid-telophase. The same pattern of zoning is found in cells entering mitosis in the presence of colcemid, but is followed by some repopulation of the inner zone by a small minority of organelles after approximately 2 h of arrest. Centrioles are particularly prone to becoming enmeshed within the 'ball' of entangled c-metaphase chromosomes. An unusually high degree of pairing of cytoplasmic membranes, probably rER elements, also occurs in colcemid-arrested metaphases, which may further contribute to their reduced level of protein synthesis. These have been referred to as 'confronting cisternae' (Ghadially, 1988). The zoning of the cytoplasm may result from nuclear envelope breakdown during mitosis, and is not specifically related to or associated with microtubule redeployment during spindle formation in M-phase. Differences in the extent of zoning in other cell lines are discussed in comparison with HeLa S-3 cells.