Correlation of nucleolini with fine structural nucleolar constituents of cultured normal and neoplastic cells.

Abstract

Alterations in the structure of nucleoli of normal diploid human embryo fibroblasts and of aneuploid HeLa cells produced by the conditions of in vitro culture and by treatment with thymidine have been studied by light and electron microscopy. During exponential growth of diploid cells, the dense fibrillar component of the nucleolus is mainly organized as a series of incomplete spherules containing a small and variable amount of light fibrillar material (fibrillar centers). These correspond to densely packed spherical nucleolini which are often too numerous to count or too small to resolve in the light microscope. The correlation between nucleolini and fibrillar centers becomes more striking in stationary cultures of human fibroblasts, where few large nucleolini in the light microscope correspond to few large light fibrillar centers in electron micrographs. Treatment of HeLa cells with 5 mm thymidine for 48 hr results in striking enlargement of nucleolini and fibrillar centers. It is thus clear that the nucleolini observed by light microscopy are the light fibrillar centers, with or without surrounding dense fibrillar material, observed by electron microscopy.