Biomedical Engineering Reference
In-Depth Information
Consistent with the CE cell behavior underlying germband extension, CE in
the mouse cochlea is mediated by Myosin II and planar polarization of
E-/N-cadherin, both of which are presumably associated with a force-
generated process (
Chacon-Heszele et al., 2012; Yamamoto, Okano, Ma,
Adelstein, & Kelley, 2009
). In contrast to PCP-independent mechanisms
during germband extension, core PCP mutants exhibit wider and shorter
cochlear ducts (
Montcouquiol et al., 2003; Wang, Guo, et al., 2006;
Wang, Hamblet, et al., 2006; Wang et al., 2005
), suggesting
PCP-dependence during cochlear CE. Interestingly, during cochlear CE,
polarized localization of Cadherins is altered in the
vangl2
mutants,
suggesting core PCP signal and classical Cadherins mediate this process
(
Chacon-Heszele et al., 2012
). Likewise,
fat4
and
ds
mutants show the
cochlea CE phenotype (
Mao et al., 2011
). However, the elongation defect
might account for defective oriented cell division as well which has been
implicated for PCP. To clarify what is the primary defect during cochlear
CE awaits further investigation.
4.5. PCP mediating cartilage elongation
It appears that the elongation of developing cartilages involves morphogenesis
of mesenchymal cells, reminiscent of CE during gastrulation. Some of the PCP
mutant fish (
gpc4
and
wnt5b
) show elongation defects in jaw cartilages, thereby
exhibiting a hammer-like head structure (
LeClair et al., 2009; Rauch et al.,
1997
). However, it is unclear whether this process is dependent largely on
CE as cell proliferation significantly accounts for the elongation. Indeed, it
seems to be the case for cell proliferation, contributing to the elongation of
the mouse limb cartilage. A distal to proximal gradient of Wnt5a regulates
the coordinated proliferation and differentiation of chondrocytes in the
mouse limb (
Yamaguchi et al., 1999
). This process is mediated by its
receptor Ror2, which in turn phosphorylates Vangl2 and induces
asymmetric localization of Vangl2, propagating an activity gradient of
Vangl2 in the proximal direction (
Gao et al., 2011
). In support of this,
ror2
mutants abolish Vangl2 activity gradient and localization, and
ror2;vangl2
double mutants phenocopy the
wnt5a
limb phenotype (
Gao et al., 2011
).
4.6. PCP mediating CE in primitive streak formation in chick
During chick streak formation prior to gastrulation, global cell flow-like
polonaise movements within an epithelial sheet of the epiblast dictate the
position of streak formation (
Cui et al., 2005
). These epithelial cells undergo
cell intercalations, reminiscent of CE, contributing to the elongation of the
primitive streak (
Lawson & Schoenwolf, 2001; Voiculescu et al., 2007
).
