Quantifying Subcellular Growth Dynamics using Quantitative Phase Imaging

Abstract

Unregulated growth has a drastic effect on the health of organisms. Unbalanced biomass production and degradation within cells can lead to diseases including diabetes, cancer, and organ hypertrophy. Understanding such growth dysregulations and the development of treatments requires understanding growth. Average growth of cell populations can be measured based on proliferation, while more advanced growth measurement approaches study single cells and can extract cell-to-cell heterogeneity information. We have developed a technique that extends further to measure localization of growth within single cells, using quantitative phase imaging (QPI) microscopy technique.QPI measures the phase shift of light as it passes through a sample, which is linearly proportional to cell biomass in the light path. As a result, QPI data show the changing biomass distribution within cells. Cell growth is commonly measured by QPI as the rate of change of biomass in whole cells over time. This approach has previously been shown to rapidly measure single cell growth and growth inhibition by drugs or therapies. Our work expands the scope of QPI further with an algorithm that utilizes the biomass distribution data to output a discretized subcellular growth map.Our approach is based on solution of a mass balance that considers biomass advection in subcellular regions. Observed changes in mass within each region of the cell can be caused by either advection of mass or biosynthesis/degradation. We can directly measure the change in biomass in each subcellular volume using QPI. We then measure the velocity of mass movement using particle image velocimetry on QPI images. Combining these two allows us to measure the amount of biosynthesis in each subcellular region. Our approach visualizes subcellular growth dynamics in real-time and quantify intracellular growth inhibition in response to drug treatments targeting cell growth mechanisms.