Control of size and growth in mammalian cells
The ultimate size of a cell is a result of the balance between cell growth and division which halves the cell size, the dividing cell being almost twice the size of each daughter cell. Cell size is time-invariant, meaning that the cycles of growth and division are coupled. Previous studies demonstrated that some eukaryotic cells have a size control mechanism coordinating cell size with cell division. The aim of EU-funded CELLCYCLEGROWTHSIZE (Cell growth and size homeostasis in proliferating mammalian cells) project was to investigate growth/cell division coordination in proliferating mammalian cells. The study's main focus was on developing methodologies to explore this fundamental process. Scientists established a functional laboratory and a number of methods for analysis of suspension and adherent cells. They developed a mechanical cell synchroniser and optimised protocols for size-based separation for adherent and unattached mammalian cells. Importantly, they demonstrated that size-based separation by cytometry can be utilised for purifying cells at a particular growth stage (G1) without synchronising drugs. Five cell lines of human and mouse origins carrying cell cycle fluorescence markers were derived for future applications. Analysis of L1210 lymphoblastic cells using developed methodologies showed a decrease in growth rate variability at the transition from proliferation to division. This observation suggests the presence of a threshold for growth to maintain size homeostasis. Studies with L1210 growing in limiting media conditions versus rich media demonstrated that growth rate forms the threshold for transition to cell division from proliferation stage. In the limiting conditions, the length of the G1 phase was extended until the cells reached a signature size at which they were able to go through the G1-S transition. Measurements of the cell dry mass revealed a size-dependent growth in adherent cells as well. In conclusion, CELLCYCLEGROWTHSIZE led to the development of essential methods and protocols for investigating cell growth and size homeostasis. Experimental results provide proof of the need for a cell-autonomous mechanism that coordinates cell cycle and cell growth.
Keywords
Mammalian cells, cell size, cell growth, CELLCYCLEGROWTHSIZE, size homeostasis