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Nucleolar "Caps"—a Morphologic Entity Produced by the Carcinogen 4-Nitroquinoline N-Oxide^*

( Department of Pathology, University of Texas Southwestern Medical School, Dallas, Texas)

Distinctive morphologic changes produced by 4-nitroquinoline N-oxide in Chang liver cells have been demonstrated by means of histologic stains, electron microscopy, and time-lapse motion picture studies of the phase-contrast microscopic images of living cells. The principal changes include: (a) nucleolar exhaustion manifested by a progressive decrease in the size of the nucleoli, (b) fusion of the nucleoli, and (c) separation of the pars amorpha and the nucleoloneme to produce two types of nucleolar "caps." The possible relationships between these morphologic changes and the known biochemical activities of 4-nitroquinoline N-oxide are discussed.

^* This research was supported by Tobacco Industries Research Grant No. 8778 and Damon Runyan Fund No. 8773.

Received 9/ 6/62.