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J. Cell Biol.,
Volume 142, Number 1, July 13, 1998 181-190
Austrian Academy of Sciences, Institute of Molecular Biology, Department of Cell Biology, A-5020 Salzburg, Austria
By co-injecting fluorescent tubulin and vinculin into fish fibroblasts we have revealed a "cross
talk" between microtubules and early sites of substrate
contact. This mutuality was first indicated by the targeting of vinculin-rich foci by microtubules during their
growth towards the cell periphery. In addition to passing directly over contact sites, the ends of single microtubules could be observed to target several contacts in
succession or the same contact repetitively, with intermittent withdrawals. Targeting sometimes involved
side-stepping, or the major re-routing of a microtubule,
indicative of a guided, rather than a random process.
The paths that microtubules followed into contacts
were unrelated to the orientation of stress fiber assemblies and targeting occurred also in mouse fibroblasts
that lacked a system of intermediate filaments. Further
experiments with microtubule inhibitors showed that
adhesion foci can: (a) capture microtubules and stabilize them against disassembly by nocodazole; and (b),
act as preferred sites of microtubule polymerization,
during either early recovery from nocodazole, or brief
treatment with taxol. From these and other findings we
speculate that microtubules are guided into substrate
contact sites and through the motor-dependent delivery of signaling molecules serve to modulate their development. It is further proposed this modulation provides
the route whereby microtubules exert their influence
on cell shape and polarity.
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