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In-Depth Information
recycle the growth cone's plasma membrane and underlying cytoskeleton in
three functionally distinct regions, the central domain, the transition zone,
and the peripheral domain (
Dent & Gertler, 2003
)(
Fig. 2.1
). These three
domains can be characterized based on their membrane, filamentous actin
(F-actin), and microtubule dynamics (
Jornvall, Reissmann, Andersson,
Mehrkash, & Ibanez, 2004; Kamiguchi, 2006
).
0s
15s
30s
75s
215s
A
f
e
l
l
l
l
f
cd
c
c
e
B
C
Lamellar
protrusion
Peripheral
domain
Peripheral
domain
Filopodial
protrusion
F-actin
Transition
Engorgement
Transition zone
Central
domain
Central
domain
Microtubules
Consolidation
F-actin
Consolidation—
mediated
endocytosis
Nascent neurite
Neurite shaft
Figure 2.1 The growth cone's vesicular matrix supports protrusion, engorgement, and
consolidation necessary to elongate and steer neurites. (A) Time-lapse images of a ret-
inal ganglion cell growth cone in culture. Both lamellipodial (l), membranous sheets, and
filopodia (f), spikes, protrude from the central domain (cd). At t¼0, a lamellipodium in-
itiates (l, arrowhead) and protrudes over the next 30 s. This lamellipodium engorges (e,
arrow) with material from the central domain between 30 and 75 s. The previous central
domain advances to fill the lamellipodium by 215 s (compare dotted line, t¼75 and
215 s) as the previous central domain consolidates (c, double arrows) into nascent neu-
rite. Time in seconds is indicated. Bar is 10 mm. (B) Schematic of vesicle dynamics during
growth cone advance. Vesicles carrying distinct lipid and protein cargos and organelles
like mitochondria are transported on microtubules from the central domain, through
the transition zone, and into the peripheral domain to support filamentous actin
(F-actin,
<<<
) based lamellar and filopodial protrusions. (C) As the growth cone
advances, protrusions engorge with cytoskeleton, vesicular cargos, and organelles
forming a new central domain that can support new cycles of lamellipodial and
filopodial protrusion. As the central domain advances, the previous central domain con-
solidates (double arrows, (B) and (C)) around bundledmicrotubules into nascent neurite.
During consolidation, proteins and lipids forming the previously spread base of the
growth cone are endocytosed and either recycled or degraded.
