Biomedical Engineering Reference
In-Depth Information
Anterior
Wnt
gradient
?
?
?
?
?
Floor plate
Posterior
Figure 6.4 Possible growth cone
-
growth cone interactions duringmidline crossing and
anterior turning of commissural axons.
same time cross the midline at the same time and turn at the same time
(
Fig. 6.4
). It takes many hours (8-9 h) to cross the midline and 1-2 h to turn
anteriorly (Y. Zou lab unpublished results). There is plenty of time for com-
missural neurons and their axons to interact with each other, although there
have been no studies addressing this possibility so far. If commissural axon
growth cones interact with each other, the global anterior turning of this
“sheet” of commissural axon growth cones is highly reminiscent of planar po-
larity. Furthermore, a sheet of axons may detect greater concentration drop
than individual growth cones if they interact with each other. Alternatively,
growth cones may not talk to each other. But rather, they work individually
because they have sensitive filopodia to detect large enough concentration
drops. These intriguing possibilities deserve further investigation.
8. IS THIS CELL POLARITY-BASED SIGNALING SYSTEM
A GENERAL GROWTH CONE STEERING MECHANISM?
By studying how Wnts signal in growth cones, we learned that the
growth cone uses both A-BP and PCP signaling pathways that are essential
for cell and tissue polarity in epithelia to control the direction of turning
