Are opposite-polarity motors coordinated?
S. P. Gross, M. A Welte, S. M. Block, E. F. Wieschaus
(2002). "Coordination
of opposite-polarity microtubule motors" J. Cell Biol. 156:715-724. Abstract
Movement of cellular organelles often involves multiple molecular motors.
A common pattern is bi-directional transport along  microtubules:
Cargoes simultaneously engage plus- and minus-end directed motors and switch
travel
direction frequently.
Do these motors engage in a tug-of-war (upper panel) or are they coordinated
to avoid interfering with each other's activity (lower panel)?
To distinguish
between these models, we used a Drosophila system that allows us to combine
genetic analysis with biophysical measurements. We impaired the minus-end
transport machinery using dynein and dynactin mutations and then investigated
whether
plus-end motion of embryonic lipid droplets was improved or disrupted.
These alterations of minus-end motor activity cause a surprisingly severe
impairment of plus-end motion. Our measurements make it very unlikely that
the motors
on the droplets compete to determine the direction of movement. Instead,
these
results support the notion that plus- and minus-end motors are coordinated,
such that one set of motors is switched off when the other is controlling
motion. Our data suggest that the dynein cofactor dynactin may provide
an inroad for
unraveling the mechanism of this coordination.
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