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Movies |
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Simulations
of molecular motors.
Frank in collaboration
with
Dr J-F. Chauwin (CIRCS post-doctoral fellow at
CIRCS), and Prof
Jorge José (director of CIRCS), developed
simple mechanical models of molecular motors, firstly to model
gliding-assay experiments, and then in order to understand their
role in mitotic-spindle formation. |
Spidle and Gliding Assay
The simulations here recreate attempt to model the work of Howard et al.
(Nature, 1989). In their gliding assay experiment, they coated a microscope slide with
kinesin (which we show as little green dots), causing the tail-domains to stick to
the surface. A microtubule (the stick-like object) was then dropped onto the surface,
and propelled along by the action of the motors.
Howard et al. studied the speed of this translation as a function of the density of
motors attached to the slide, and found that it was more or less constant, over several
orders of magnitude. Because the microtubule has a polarity, I have indicated the plus
end in some of the newer movies. The kinesins try to move towards this end, which means
the other (`minus') end leads. |
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Title: Spindle
m200-d100 (MPG, 6.6Mb)
Mitotic spindle, 200 microtubules, 100 dyneins. The microtubules are
shown in red, with the plus ends indicated in blue (all colors are,
of course, false).
m200-d500 (MPG, 1.8Mb)
Mitotic spindle, 200 microtubules, 500 dyneins.
The microtubules are shown in red, with the plus ends
indicated in blue (all colors are, of course, false).
m200-d1000 (MPG, 1.4Mb)
Mitotic spindle, 200 microtubules, 1000 dyneins. The microtubules
are shown in red, with the plus ends indicated in blue (all
colors are, of course, false).
m200-d2000 (MPG, 1.8Mb)
The mitotic spindle, as formed by motors, using 200 microtubules,
and 2000 dyneins. The microtubules are shown in red, with the
plus ends indicated in blue (all colors are, of course, false).
No motors are shown in this movie. The white spheres at the center
of the image represent the chromatin-coated latex spheres in the
experiments of Heald et al., which provide an anchoring site for
the kinesins.
m300-d1000 (MPG, 1.86Mb)
The mitotic spindle, this time with 300 microtubules, and only 1000 dyneins.
Notice how the smaller ratio of dyneins to microtubules
(compared to the movie above) results in a slower (and less symmetrical)
convergence to a spindle-like structure.
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Title: Gliding Assay
Sigma5 (MPG, 0.84Mb)
Low motor density (5 µm-2).
This is about the minimum density at which we get consistent motion in our simulations,
based on the parameters that we believe to be the best match to the physical behavior
of the motors.
Sigma10 (MPG, 0.84Mb)
Intermediate motor density (10 µm-2).
At this density, the microtubule is pretty securely anchored to the substrate, and
moves relatively smoothly. The substrate is 20 µm square, while the microtubule is 10
µm in length. As you can see, the microtubule moves a distance equal to its own length.
There are still some noticeable angular fluctuations.
Sigma100 (MPG, 0.09Mb)
High motor density. (100 µm-2)
Notice how the angular deviations are much smaller at high motor density. The
microtubule is rarely free, but is held by many dozens of motors, and therefore has
less freedom.
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