Cell cycle arrest and morphological alterations following microinjection of NIH3T3 cells with Puraα

Abstract

Levels of Purα, a protein implicated in control of both DNA replication and gene transcription, fluctuate during the cell cycle, being lowest in early S phase and highest just after mitosis. Here we have employed a new video time-lapse technique enabling us to determine the cell cycle position of each cell in an asynchronous culture at a given time and to ask whether introduction of Purα protein at specific times can affect cell cycle progression. Approximately 80% of all NIH3T3 cells injected with Purα were inhibited from passing through mitosis. Cells injected with Purα during S or G2 phases were efficiently blocked with a 4N (G2 phase) DNA level, as determined by quantitative DNA photometry of individual cells. Of the cells injected with Purα during G1 phase, 40% experienced a rapid cell death characterized by extreme cellular fragmentation. Of those G1 injected cells which remained viable, approximately equal numbers were arrested with either 2N or 4N DNA levels. Cells arrested by Purα in G2 phase grew to cover a large surface area. These results link fluctuations in Purα levels to aspects of cell cycle control.