Abstract
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 interconnected microtubules to linear and triangular geometries to perform micro-rheology by defined oscillations of the beads relative to each other. We found 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.
Highlights
We only investigate the elastic component G′, whereas the viscous contributions G”, expressed by the viscous drag gMT of the MT, are discussed in the Supplementary Results
As we have shown in the Supplementary Results, the extents of the 1 μm large beads result in additional geometrical effects affecting the deformation and have to be considered in the future
A third implication of our findings is linked with the “mechanic transistor” function of microtubule networks, where small mechanical forces can control a large amount of momentum transport
Summary
This section introduces the relevant forces acting on a single filament and its resulting deformations as well as the relative bead displacements during an oscillation longitudinal to the MT. The forces acting on the microtubule and the forces on the beads are directly coupled through the constraint of a constant contour length L. As we show in the Supplementary Results, the measured net forces on the beads in direction lateral (y) to the filament are negligibly small, such that all effective forces due to microtubule buckling and viscous drags point only in x direction. In the tension free case the sum of forces acting on a single bead with index j can be described by the following, one dimensional equation of motion for the bead at longitudinal position xBj and the filament contour described by u(x): Foptj(xBj)
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