Physics

Nucleolus

Nucleus

Biology

Osmometer

Osmotic pressure

Gene

Fission

Biophysics

Nucleoplasm

Neutron

Cytoplasm

Osmotic shock

Nuclear physics

Chemistry

Schizosaccharomyces

Macromolecule

Saccharomyces cerevisiae

Yeast

Schizosaccharomyces pombe

Cell biology

Cell size

Chromatography

Biochemistry

eLife

The size of the nucleus scales robustly with cell size so that the nuclear-to-cell volume ratio (N/C ratio) is maintained during cell growth in many cell types. The mechanism responsible for this scaling remains mysterious. Previous studies have established that the N/C ratio is not determined by DNA amount but is instead influenced by factors such as nuclear envelope mechanics and nuclear transport. Here, we developed a quantitative model for nuclear size control based upon colloid osmotic pressure and tested key predictions in the fission yeast Schizosaccharomyces pombe . This model posits that the N/C ratio is determined by the numbers of macromolecules in the nucleoplasm and cytoplasm. Osmotic shift experiments showed that the fission yeast nucleus behaves as an ideal osmometer whose volume is primarily dictated by osmotic forces. Inhibition of nuclear export caused accumulation of macromolecules in the nucleoplasm, leading to nuclear swelling. We further demonstrated that the N/C ratio is maintained by a homeostasis mechanism based upon synthesis of macromolecules during growth. These studies demonstrate the functions of colloid osmotic pressure in intracellular organization and size control.

Control of nuclear size by osmotic forces in Schizosaccharomyces pombe