A general mechanism for cell size control in yeast

Size is a key physiological variable for cell growth. Subjected to noise, cells must employ active size control. However, the mechanistic origins of size control remain elusive. One possibility is that cells have molecular thresholds for key molecules that must be reached for division to commence. Eukaryotic cells (e.g., fission yeast) are believed to reach a concentration-based threshold. Additionally, it has been found that yeast cells follow a "sizer" control mechanism, targeting a specific size before division, but the origins of this control strategy remain unclear. Here, we introduce a generic model that relies on multiple concentration checkpoints for different cell components. Our results show that if at least one checkpoint relies on a molecule whose concentration is proportional to volume, then sizer control dominates the control strategy. We show that this model is consistent with experimental data and suggests that size control is separate from division control in yeast.