The transfer of mechanical signals through cells is a complex phenomenon. To uncover a new mechanotransduction pathway, we study the frequency-dependent transport of mechanical stimuli by single microtubules and small networks in a bottom-up approach using optically trapped beads as anchor points. We interconnect microtubules to linear and triangular geometries to perform micro-rheology by defined oscillations of the beads relative to each other, which are measured with 3D back focal plane interferometry. We find a substantial stiffening of single filaments above a characteristic transition frequency of 1-30 Hz depending on the filament’s molecular composition. Below this frequency, filament elasticity only depends on its contour and persistence length. Interestingly, this elastic behavior is transferable to small networks, where we found the surprising effect that linear two filament connections act as transistor-like, angle dependent momentum filters, whereas triangular networks act as stabilizing elements. These observations implicate that cells can tune mechanical signals by temporal and spatial filtering stronger and more flexibly than expected. In addition, we integrate a novel label-free microscopy techniques, capable of imaging freely-diffusing microtubules in real-time and independent of their orientation. We show that rotating coherent scattering (ROCS) microscopy in dark-field mode provides strong contrast also for structures far from the coverslip such as arrangements of isolated MTs and networks. We could acquire thousands of images over up to 30 minutes without loss in image contrast or visible photo damage.
Alexander Rohrbach and Matthias D. Koch, "Non-linear momentum transfer of single microtubules and small networks investigated by multiple traps and BFP tracking (Conference Presentation)," Proc. SPIE 10723, Optical Trapping and Optical Micromanipulation XV, 107230F (Presented at SPIE Nanoscience + Engineering: August 19, 2018; Published: 17 September 2018); https://doi.org/10.1117/12.2324043.5836018667001.
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