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Single-Cell Biophysics: Measurement, Modulation, and Modeling
Poster Abstracts
141
86-POS
Board 43
Cell Cycle-Dependent Fluctuations of Protein Mobility in Cytoplasm of Hela Cell
Krzysztof Szczepanski
, Karina Kwapiszewska, Robert Holyst.
Institute of Physical Chemistry PAS, Warsaw, Poland.
Great deal of life-sustaining processes are diffusion-limited and viscosity of cytoplasm may
influence the diffusion rates. Up to date no one attempted to measure how viscosity of cytoplasm
changes throughout the cell cycle. Current research focuses rather on short time-stamps in cell
life. Our research aims to measure fluctuations of rate of diffusion of example protein during cell
cycle and to give possible explanations of any changes observed.
We studied diffusion of enhanced green fluorescent protein (eGFP) in cell cytoplasm of HeLa
eukaryotic cell line using fluorescence correlation spectroscopy (FCS). Monomeric eGFP was
chosen as well-known and biologically-neutral probe which has size comparable to cell
cytoplasm content. Observations made on this basis could be easily transferred to other
cytoplasmic proteins. To ensure uniform progress through cell cycle, cells were first
synchronized at the G1/S phase transition using aphidicolin and then allowed to grow.
Our results clearly show fluctuations in diffusion coefficients of eGFP travelling through the
cytoplasm of cells (as compared to diffusion in buffer). These fluctuations seem to be connected
with events happening inside cells as they prepare for division and undergo the mitosis.
Throughout S and G2 phases diffusion decreases relatively slowly until the division, when the
decrease is sharp. Then, during G1 phase, it slowly but steadily increases. Our results could hint
at possible not yet studied mechanism of modulation of cellular activities through changes in
rates of diffusion of proteins in cytoplasm. Alternatively these changes could also originate from
cellular volume fluctuations. This could be the first step towards understanding whether viscosity
could regulate internal processes of the cell.