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Vol. 18, Issue 9, 3523-3532, September 2007

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The Size of the Nucleus Increases as Yeast Cells Grow

Paul Jorgensen^*,,, Nicholas P. Edgington, Brandt L. Schneider^||, Ivan Rupe, Mike Tyers^*,, and Bruce Futcher^¶

*Department of Medical Genetics and Microbiology, University of Toronto, Toronto, ON M5S 1A8, Canada; Samuel Lunenfeld Research Institute, Toronto, ON M5G 1X5, Canada; Department of Biology, Southern Connecticut State University, New Haven, CT 06515; ^||Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430; and ^¶Department of Molecular Genetics and Microbiology, SUNY at Stony Brook, Stony Brook, NY 11794

Submitted November 1, 2006; Revised June 8, 2007; Accepted June 19, 2007
Monitoring Editor: Orna Cohen-Fix

It is not known how the volume of the cell nucleus is set, nor how the ratio of nuclear volume to cell volume (N/C) is determined. Here, we have measured the size of the nucleus in growing cells of the budding yeast Saccharomyces cerevisiae. Analysis of mutant yeast strains spanning a range of cell sizes revealed that the ratio of average nuclear volume to average cell volume was quite consistent, with nuclear volume being 7% that of cell volume. At the single cell level, nuclear and cell size were strongly correlated in growing wild-type cells, as determined by three different microscopic approaches. Even in G1-phase, nuclear volume grew, although it did not grow quite as fast as overall cell volume. DNA content did not appear to have any immediate, direct influence on nuclear size, in that nuclear size did not increase sharply during S-phase. The maintenance of nuclear size did not require continuous growth or ribosome biogenesis, as starvation and rapamycin treatment had little immediate impact on nuclear size. Blocking the nuclear export of new ribosomal subunits, among other proteins and RNAs, with leptomycin B also had no obvious effect on nuclear size. Nuclear expansion must now be factored into conceptual and mathematical models of budding yeast growth and division. These results raise questions as to the unknown force(s) that expand the nucleus as yeast cells grow.

Present address: Department of Systems Biology, Harvard Medical School, Boston, MA 02115.

Address correspondence to: Bruce Futcher (bfutcher{at}ms.cc.sunysb.edu), Mike Tyers (tyers{at}mshri.on.ca), or Paul Jorgensen (paul_jorgensen{at}hms.harvard.edu).

Abbreviations used: CFP, cyan fluorescent protein; DIC, differential interference contrast; EM, electron microscopy; ER, endoplasmic reticulum; GFP, green fluorescent protein; N/C, nuclear to cell volume ratio; YFP, yellow fluorescent protein.