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Figure 5.6 mDia1 stabilizes non-centrosomal microtubules. (A) In centrosome-containing
cytoplasts, microtubules form a radial array with minus-ends attached to the centrosome.
(B) Cytoplasts lacking a centrosome contain only a few microtubules; the amount of
tubulin polymer is much less than in centrosome-containing cytoplasts. (C) Centrosome-
free cytoplasts expressing active mDia1 preserve their bipolar shape and contain many
microtubules aligned along their axes. The amount of tubulin polymer is of the same order
of magnitude as in centrosome-containing cytoplasts. Staining with anti-tubulin antibody.
Photograph (A) is reproduced with permission from Chausovsky et al. (2000)
this group can also be found in association with the centrosome (see, for
example Rehberg and Graf (2002)). This indicates possible additional
functions of these proteins in the control of minus end dynamics and/or
their attachment to the centrosome. This is consistent with the centrosomal
localization of mDia1, as mentioned above.
There is no direct information yet concerning possible interactions of
mDia1 with any of these microtubule-associated proteins. One interesting
possibility can be inferred from data on the composition of the dynein-
dynactin complex. An essential component of this complex, is a filament-
forming actin-related protein 1 (Arp1) known also as centractin, which is
more homologous to actin than other Arps (Holleran et al., 1998). Moreover,
Arp1 not only binds to other components of dynactin complex, like
p150Glued (Waterman-Storer et al., 1995), but also to several types of
genuine actin-binding proteins such as barbed end capping protein (Schafer
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