의생명시스템학부

제목: Dynamics of single-cell biophysical properties and bioenergetics during the cell cycle

내용:

Cells undergo dynamic changes in cell size, shape and mechanics during the cell cycle. However, studying the biophysical dynamics is challenging because both the magnitude and duration of the changes are heterogeneous across the cell population. In this talk, we present new methods to monitor single-cell mechanical properties and bioenergetics during the full cell cycle with temporal resolution of ~1 min. We utilize the suspended microchannel resonator (SMR) which is a fluid-filled cantilever capable of measuring cell buoyant mass by the change of SMR resonant frequency. First, we quantify mechanical properties via acoustic scattering of waves from a cell inside the SMR. Through simulations, experiment with hydrogels and chemical perturbation of cells, we show that our readout from acoustic scattering measures stiffness. Mouse lymphocytic leukemia L1210 cells maintained constant stiffness throughout interphase but displayed dynamic changes during mitosis. Next, we monitor mitochondrial membrane potential of single L1210 cells and demonstrate that mitochondrial membrane potential increases during mitosis. By using an electrical circuit model of mitochondria, we quantify the time-dynamics of mitochondrial membrane potential under normal and perturbed conditions to extract mitochondrial ATP synthesis rates in mitosis. We found that mitochondrial ATP synthesis decreases by approximately 50 % during early mitosis and increases back to G2 levels during cytokinesis. Lastly, we monitored L1210 cell growth efficiency during normal proliferation and polyploidization. This was enabled by the development of large-channel SMR that allow us to monitor buoyant mass of single cells ranging from 40 pg (small pseudodiploid cell) to over 4,000 pg. We found that cell growth efficiency increases, plateaus, and then decreases as cell cycle proceeds. This growth behavior repeats with every endomitotic cycle as cells grow into polyploidy. Overall, growth efficiency changes 33% throughout the cell cycle. In contrast, increasing cell mass by over 100-fold during polyploidization did not change growth efficiency, indicating exponential growth.