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* Center for Neurologic Diseases, and Growth cones extend dynamic protrusions
called filopodia and lamellipodia as exploratory probes
that signal the direction of neurite growth. Gelsolin, as
an actin filament-severing protein, may serve an important role in the rapid shape changes associated with
growth cone structures. In wild-type (wt) hippocampal
neurons, antibodies against gelsolin labeled the neurite
shaft and growth cone. The behavior of filopodia in cultured hippocampal neurons from embryonic day 17 wt
and gelsolin null (Gsn
Division of Experimental Medicine, Department of Medicine, Brigham and Women's
Hospital, Harvard Medical School, Boston, Massachusetts 02115; and § Mouse Biology Programme, European Molecular Biology
Laboratory, 00015 Monterotondo/Rome, Italy
) mice (Witke, W., A.H. Sharpe,
J.H. Hartwig, T. Azuma, T.P. Stossel, and D.J. Kwiatkowski. 1995. Cell. 81:41-51.) was recorded with time-lapse video microscopy. The number of filopodia along
the neurites was significantly greater in Gsn
mice and
gave the neurites a studded appearance. Dynamic studies suggested that most of these filopodia were formed
from the region of the growth cone and remained as
protrusions from the newly consolidated shaft after the
growth cone advanced. Histories of individual filopodia
in Gsn
mice revealed elongation rates that did not differ from controls but an impaired retraction phase that
probably accounted for the increased number of filopodia long the neutrite shaft. Gelsolin appears to function
in the initiation of filopodial retraction and in its
smooth progression.
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