Microtubules are highly dynamic structures that rapidly assemble and
disassemble. Each is composed of building blocks bound together, like a
string of small magnetic beads - and just as magnets have poles, these
building blocks have "plus" and "minus" ends.
Growth occurs at the plus
end, where new blocks are added. As this happens, new microtubules
radiate out from a common center, extending in all directions as they
‘A molecular motor, called Kinesin-14, helps to guide the formation of a new microtubule along an existing one, and so directs the formation of bundles.’
Somehow, the cell wrangles the growing microtubules, bringing them
into clustered bundles that extend in common directions. Thus far, it's
been unclear how this process occurs.
New work led by a Rockefeller University scientist offers insight as
to how cells align their microtubules in order to bundle them. The
study, published in Cell
, describes how two proteins work together to guide the growth of a new microtubule along an existing one.
A team of researchers led by Alipasha Vaziri, an associate professor and head of the Rockefeller's Laboratory's of Neurotechnology and Biophysics,
has found that a molecular motor, called Kinesin-14, helps to guide the
formation of a new microtubule along an existing one, and so directs
the formation of bundles.
This protein's unusual ability to walk in both directions along the
filament makes this possible. "It has a preference for movement towards
the minus end, but the smallest bit of force can make it change
direction and move toward the plus end," says Vaziri says, who was
working at the Research Institute of Molecular Pathology in Vienna at
the time the research was conducted.
His team found that, from its vantage point at the minus-end of an
existing microtubule, Kinesin-14 attaches to a second protein that is
bound to the plus end of a growing microtubule. This interaction nudges
Kinesin-14 backward, prompting it to guide the growth of the new
microtubule in parallel with the older one.
The team showed that a wide range of animal cells employ this
mechanism. "While we made our original observation in yeast, we were
able to show the same phenomenon for human and fly cells. This means
that this is a general mechanism conserved throughout evolution," Vaziri