The cover image for the August 2 issue of Biophysical Journal shows spontaneous strains of actin stress fibers in a living cell (rat aortic smooth muscle A7r5 cell), which is composed by overlaying the strain values shown in color onto the original confocal microscope image. These strains are obtained by using the continuum mechanics–based fluorescence recovery after photobleaching analysis that we developed in this paper. This novel method allows for simultaneous evaluation of chemical and mechanical properties of stress fibers within cells such as binding off-rate, intracellular active movement, and microscopic strain.
The basic motivation to create this cover image, of all the figures in the paper, was to unveil the intracellular spatial distribution of the microscopic strain of stress fibers. Interestingly, stress fibers undergo constant turnover within cells as our whole body does the same to replace old cells with new ones, eventually maintaining the health of the hierarchical living system. Thanks to this turnover, stress fibers and cells are able to adapt to change in intracellular/extracellular environments. As shown in the cover image and other figures in the paper, we realized quantification and visualization of the complicated chemomechanical properties in living cells. This helps us decipher how individual molecules dynamically construct stress fibers and in turn enable cellular structural and functional adaptation to surroundings.
Through our study and this cover image, we put forward a powerful way to analyze the complicated chemomechanical behaviors of living cells. Our method is widely useful not only for actin stress fibers but also for various types of subcellular/multicellular structures subjected to mechanical and biochemical perturbations and would thus contribute to further understanding of the adaptive nature of living systems.
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-Takumi Saito, Daiki Matsunaga, and Shinji Deguchi