Planar Cell Polarity in Coordinated and Directed Movements - Current Topics in Developmental Biology - page 96

Importantly, abrogation of core PCP genes interferes with cell intercalations,
thereby leading to inhibition of streak formation ( Voiculescu et al., 2007 ).
These observations suggest that the PCP pathway plays a pivotal role in
regulating elongation of the body axis through CE regardless of prior to or
during gastrulation.
5. PCP IN MEDIATING COLLECTIVENESS AND
POLARIZED BEHAVIORS
5.1. CE and contact inhibition of locomotion
The separable convergence and extensionmovements in fishmight be due to the
density of lateral mesoderm cells lesser than that of the Xenopus gastrula. This in-
spires us to interpret CE at least in zebrafish as part of collective cell migration.
Howdo lateral mesodermcells read their densitywhile undergoing convergence
movement? By analogy to collective migration of neural crest cells ( Carmona-
Fontaine et al., 2008 ), one possibility is that cells undergoing CE may involve
contact inhibition of locomotion (CIL) in a dispersed location and utilize the
Wnt/PCP pathway to ensure this event to occur. In other words, a possible role
for the Wnt/PCP pathway is to suppress “randomness” and to maintain proper
cell orientation. Consistent with this idea, N-cadherin is required for proper dor-
sal convergence as well as CIL in neural crest cells ( Theveneau et al., 2010; von
der Hardt et al., 2007 ). Moreover, the ability of the Wnt/PCP pathway to
modulate actomyosin is correlated with suppression of ectopic blebs, which
can be induced by abrogation of myosin phosphatase in cells undergoing CE
( Weiser et al., 2009 ). In other words, if the Wnt/PCP activity is
compromised, randomness of lateral mesoderm cells increases as a result of
increased blebbing activity or possibly owing to loss-of-CIL behavior of the cells.
During collective migration of prechordalprogenitors,ifcellcohesionisre-
duced in wnt11 mutants, the cells reduce net migration while remaining tightly
packed ( Ulrich et al., 2005 ). However, proper cell cohesion can be dispensable
for net migration of prechordal plate progenitors, as defective migration of
wnt11 -mutant cells is restored if the cells acquire increased motility while
retaining reduced cell cohesion ( Kaietal.,2008 ). Interestingly, in this situation,
the cells migrate more randomly, presumably due to reduced CIL behavior
with increased motility. This is consistent with the idea that the Wnt/PCP
pathway plays a fundamental role in reducing “randomness.” This inspires us
to hypothesize that mesenchymal cells utilize the common strategy by which
to suppress randomness regardless of their density.