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In-Depth Information
Peterson and Ron Vale [44]) specifically to the “cortex” of these artificial
cell-like chambers. In Figure 4.11c, we show preliminary results on how a mi-
crotubule aster that is nucleated by a centrosome (a gift from Michel Bornens)
is trying to maintain a position close to the center of the chamber while being
subject to constant attempts by dynein molecules to pull the aster towards
the chamber edge. To understand what balance of pulling and pushing forces
is needed to keep the aster actively centered, we plan to vary the relative of
amount of dynein-interacting microtubule ends by reducing or enlarging the
thickness of the gold layer (and thereby the amount of surface area available
for motor proteins to attach).
4.9 Controlling Microtubule Organization
in vivo
Forces generated by growing or shrinking microtubules provide only one of
a large repertoire of mechanisms by which cells organize the microtubule cy-
toskeleton. For example, in the organization of the fission yeast interphase
array, additional important ingredients are microtubule-associated proteins
that control microtubule nucleation at the nuclear membrane and elsewhere,
proteins that allow for anti-parallel bundling at mid-cell, motor proteins that
slide anti-parallel microtubules towards the cell center, and microtubule end-
binding proteins that travel to the cell ends and locally create a different
protein environment.
In general, the activity of molecular motors is an essential component of
most microtubule-based force generation processes in cells. In the case of chro-
mosomes motions in the mitotic spindle, it is clear that a number of different
motor proteins associated with chromosomes, kinetochores, microtubule poles,
and anti-parallel microtubule arrays somehow work together with microtubule
polymerization and depolymerization processes. Understanding the complex
regulation of all these antagonistic forces and the versatility that this creates
for a dynamic and responsive control of the microtubule array in different
cell types and situations, provides an exciting challenge in cell biology and
cell biophysics research. It seems evident, however, that mechanical aspects
related to cell shape and size, microtubule elastic properties, and biochemi-
cal response to force generation need to be an integral part of understanding
functional microtubule organization in cells.
Acknowledgements
We thank former members of our group, Mathilde de Dood, Martijn van
Duijn, Cendrine Faivre-Moskalenko, Astrid van der Horst, Marcel Janson, Ja-
cob Kerssemakers, and Guillaume Romet-Lemonne for their contribution to
work that is presented in this chapter. We thank Henk Bar, Niels Dijkhuizen,
Roland Dries, Johan Herschied, Marco Konijnenburg, Chris Retif, and Dun-
can Verheij for technical support at AMOLF. We also thank collaborators
