3D confinement physically regulates cell cycle progression in budding yeast

Molecular control over cell division is traditionally studied using liquid broths or 2D flat-plate cultures — neither of which recapitulate the complex visco-elasto-plastic properties of 3D natural habitats such as tissues, mucus, and soil. Consequently, how such regimes of physical confinement influence proliferative growth remains unknown. Here, by engineering mechanically tunable and transparent growth matrices, we directly visualize yeast budding across 3D viscoelastic regimes. We discover that elevated physical confinement drastically prolongs budding intervals without causing physiological defects. Remarkably, reduced proliferative rates are not associated with transcriptional signatures of mechanosensation or cell cycle dysregulation. Rather, 3D confinement physically constrains the volumetric growth of incipient buds — manifesting as delayed cell cycle progression. Hence, our findings establish a fundamentally unique form of physical regulation over eukaryotic cell division.