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Control of Nuclear Division in Normal but Not in Neoplastic Mouse Cells¹

Department of Microbiology and Pathology, University of Utah Medical Center, Salt Lake City, Utah 84132, and Department of Pathology, Veterans Administration Hospital, Salt Lake City, Utah 84113

A control mechanism that limits nuclear division is present in contact-inhibited nontumorigenic mouse BALB/3T3 cells and mouse embryo fibroblasts. In the absence of cytoplasmic division, 3T3 and mouse embryo fibroblast cells may undergo nuclear division once or occasionally twice and then stop. Also, there is no increase in the frequency of premature chromosome condensation. In non-contactinhibited tumorigenic BALB/3T12 and L-cells, nuclear division occurs repeatedly in the absence of cytoplasmic division and is therefore relatively uncontrolled. The frequency of premature chromosome condensation is markedly increased in 3T12 and L-cells unable to undergo cytoplasmic division. These observations are consistent with the hypothesis that the loss of control of nuclear division in neoplastic cells represents a characteristic defect.

¹ Supported by NIH Grant 1RO1 CA 12668-01 and intramural funds to the Salt Lake Veterans Administration Hospital.

Received 10/17/73. Accepted 2/ 6/74.