Biomedical Engineering Reference
In-Depth Information
What establishes AP-biased Pk and Dsh in cells undergoing CE? Presum-
ably, the cue can establish the AP polarity is a gradient of Nodal signal as
demonstrated in animal caps treated with different doses of Activin. Only
at the interface between high and low Activin, activities confer CE cell
behavior (
Ninomiya et al., 2004
). This hypothesis needs to be clarified
in
vivo
in future.
4. PCP REGULATING CE AND COLLECTIVE CELL
MIGRATION IN OTHER CONTEXTS
4.1. Collective migration of individual mesenchymal
cells
Neural crest cells
Neural crest cells in the cranial region of the embryo are delaminated from the
dorsal neural tube and migrate as individual mesenchymal cells in the stream.
Migrating neural crest cells are highly polarized with actin-rich processes to
orient the direction of their migration (
Matthews et al., 2008
). Despite their
individual migration, there are rare neighbor exchanges involved. There are
two mechanisms to achieve collective migration of neural crest cells. First,
contact inhibition of locomotion (CIL) allows cells to inhibit from their ran-
dom movement by collapsing their processes followed by changes in their
direction upon encountering between the two cells (
Carmona-Fontaine
et al., 2008
). Second, coattraction by which cells can attract another one at
a distance via diffusible molecule(s) maintains their coherence (
Carmona-
Fontaine et al., 2011
). Thus, these twomechanisms counterbalance each other
to permit cells to undergo collective migration. Wnt11 signaling through Dsh
and RhoA is required for polarization of migrating neural crest cells
(
Matthews et al., 2008
). Moreover, the Wnt/PCP pathway is indispensable
for CIL behaviors in that Wnt11, Fzd7, Dsh, and activated RhoA are all
accumulated at cell-cell contact in cultured neural crest cells (
Carmona-
Fontaine et al., 2008
). Together, the Wnt/PCP pathway plays a pivotal role
in regulating collective migration of neural crest cells.
—
4.2. Collective migration of a small cluster of mesenchymal
cells
Neuronal migration
In contrast to a large population of coherent sheet of prechordal plate pro-
genitors, an example of a small cluster of cohesive cells undergoing collective
migration is facial branchiomotor (FBM) neurons in zebrafish and mouse
embryos. FBM neurons are born in the rhombomere 4 of the hindbrain
and caudally migrate into the rhombomere 7 territory before projecting
—
