Protein-driven colloid-osmotic pressure controls nuclear size, organization, and function

The size of a cell's nucleus is tightly regulated and changes in nuclear size are linked to shifts in nuclear function throughout development, cell differentiation, and senescence. The precise mechanism behind this regulation, however, has been a mystery until now. In a groundbreaking study, researchers have discovered that the nuclear size is controlled by the osmotic pressure generated by proteins within the nucleus.

This osmotic pressure was found to regulate the nuclear-to-cytoplasmic ratio across various organisms, including yeast, human cells, and frog egg extracts.

The biophysical model established by the team solves a longstanding conundrum regarding how the nucleus's size is maintained. Altering the protein-driven osmotic balance affects the nuclear's physical properties, which in turn impacts chromatin organization and gene expression. When the nuclear size expands, heterochromatic structures disintegrate, subtelomeres and transposons become active, and highly expressed housekeeping genes are downregulated.

Remarkably, these global transcriptional changes mirror those observed during the nuclear enlargement process in yeast, human, and drosophila cells.

Interestingly, artificially compressing the nucleus can reverse the size-associated gene expression alterations. This discovery not only offers a quantitative, mechanistic explanation for the link between nuclear size and cell size but also positions nuclear size as a pivotal factor in managing chromatin organization and gene expression.