Cell Size Control

Cell size plays a crucial role in the function of various cell types throughout the human body, influencing organelle structure, biosynthesis, and surface transport processes. Although certain genes influencing cell size have been identified, the molecular mechanisms by which cell growth initiates cell division are largely unknown. Contrary to expectations that growth would enhance the activity of cyclin-dependent kinases (Cdks), which are known to facilitate cell division, our findings suggest the opposite. Namely, that cell growth prompts division by diluting proteins that inhibit division, specifically Whi5 in yeast and the retinoblastoma (Rb) tumor suppressor in human cells. This identified ‘inhibitor dilution’ as a critical mechanism linking cell growth with cell division. Here, we report our new findings on the distinct molecular mechanisms responsible for decreasing Rb and Whi5 concentrations in G1 phase. Our findings underscore the complex molecular strategies eukaryotic cells employ to perform the conserved strategy of diluting cell cycle inhibitors during the G1 phase to coordinate cell growth with division.