By immunogold labeling, we demonstrate that "millipede-like" structures seen previously
in mammalian cell cytoskeletons after removal of actin by treatment with gelsolin are
composed of the cores of vimentin IFs with sidearms containing plectin. These plectin
sidearms connect IFs to microtubules, the actin-based cytoskeleton and possibly
membrane components. Plectin binding to microtubules was significantly increased in cells from transgenic mice lacking IFs and was reversed by microinjection
of exogenous vimentin. These results suggest the existence of a pool of plectin
which preferentially associates with IFs but may also be competed for
by microtubules. The association of IFs with microtubules did not show
a preference for Glu-tubulin. Nor did it depend upon the presence of
MAP4 since plectin links were retained after specific immunodepletion
of MAP4. The association of IFs with stress fibers survived actin
depletion by gelsolin suggesting that myosin II minifilaments or
components closely associated with them may play a role as plectin
targets. Our results provide direct structural evidence for the hypothesis
that plectin crosslinks elements of the cytoskeleton thus leading to
integration of the cytoplasm.
