Growth cones extend dynamic protrusions called filopodia and lamellipo
dia as exploratory probes that signal the direction of neurite growth.
Gelsolin, as an actin filament-severing protein, may serve an importa
nt role in the rapid shape changes associated with growth cone structu
res. In wild-type (wt) hippocampal neurons, antibodies against gelsoli
n labeled the neurite shaft and growth cone. The behavior of filopodia
in cultured hippocampal neurons from embryonic day 17 wt and gelsolin
null (Gsn(-)) 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 n
eurites was significantly greater in Gsn(-) mice and gave the neurites
a studded appearance. Dynamic studies suggested that most of these fi
lopodia were formed from the region of the growth cone and remained as
protrusions from the newly consolidated shaft after the growth cone a
dvanced. Histories of individual filopodia in Gsn(-) mice revealed elo
ngation rates that did not differ from controls but an impaired retrac
tion phase that probably accounted for the increased number of filopod
ia long the neutrite shaft. Gelsolin appears to function in the initia
tion of filopodial retraction and in its smooth progression.