CrowdControl · CrowdControl: Identifying the mechanism underlying intracellular density homeostasis.

The cytoplasm is filled with an extremely high concentration of macromolecules that is close to the maximal physical limit. Such a tight packing of macromolecules gives rise to a crowding effect that influences chemical reactions and protein dynamics. Changes in crowding levels are therefore predicted to have profound consequences on cell function. It is therefore not surprising that the overall intracellular concentration of macromolecules is very constant within a cell type, but it varies during important physiological transitions such as cell division, differentiation, and senescence. How crowding is regulated is poorly understood but feedback coupling between intracellular density and cell growth has been observed in multiple systems. The CrowdControl project will combine two unbiased screening approaches with targeted genetic manipulations and quantitative live cell imaging to identify the molecular mechanism underlying intracellular density homeostasis. Specifically, we will: (i) identify proteins that can sense intracellular density changes by performing structure sensitive mass spectrometry in cells with different levels of macromolecular crowding; (ii) perform a CRISPR-knockout screen to identify mutations that affect density homeostasis; and (iii) use quantitative live cell microscopy to investigate whether proteins identified in (i) and (ii) affect feedback coupling between intracellular density and cell growth. A better understanding of intracellular density regulation will allow the development of precise tools to alter crowding and identification of crowding sensitive proteins will give insight into what processes may respond to density changes. The results of this project will therefore be key to understanding how cells finely tune their intracellular density levels, but in addition they will also lay the basis for understanding how density changes affect cell function during the cell cycle, senescence, and differentiation.