Abstract:
The many cellular processes like cell division and axonal, vesicle and organelle
transport are largely driven by cytoskeletal elements like Microtubule (MT) and molecular
motors. There are two group of motors - Kinesin and Dynein, which walks and
transport towards plus and minus end of MT respectively. However, in presence of
both motors on single cargo or MT can lead to Tug-of-war scenarios and shows stochastic
switching in transport direction. These scenarios can have following type of
geometries, a single cargo or MT transported by two antagonistic motors and other
an aster being transported by a single type of motor. The motor-MT system can be
compared to Magneto-elastic system (an example of Duffing oscillator) where motor
and MT corresponds to magnet and metallic strip respectively. On external forcing,
Magneto-elastic system shows Force Induced Stability (FIS). It would be interesting to
know whether in vivo motor-MT system uses Force Induced Directionality (FID).
We perform in silico gliding assay using Cytosim, a Langevin-Brownian particle
simulator. Gliding assay setup geometry consists of MT gliding on immobilized mix
motors. Control simulations were performed in absence of external forcing. Cytosim
is modified for implementing the forcing using fluid flows to study the effect of external
forcing. In order to test the predictions from simulations, we attempt to purify kinesin
and perform mix multi motor gliding assay and study effect of forcing using optical trap.
Tug-of-war and stochastic switching were observed in control simulations. The
developed parameters, Directionality and bias are able to quantify directional instability
in MT transport and can distinguish between forced and non-forced scenarios.
The effect of external forcing is studied and results shows signs of FID for forcing (frequency - 10Hz and amplitude - 1 um) value. Further analysis is required to find optimal
forcing parameters which can led to FID in motor-MT system and to understand the
underlying phenomenon and relate to in vivo scenarios like cytoplasmic flows, actin
polymerization.
