Planar Cell Polarity in Coordinated and Directed Movements - Current Topics in Developmental Biology - page 98

signal in turn modulates Wnt/PCP pathway activities ( Davidson et al., 2006;
Goto et al., 2005; Munoz et al., 2006 ), plays an important role in regulating
cell polarization underlying CE in Xenopus . The ability of Vangl2 to
modulate deposition of the extracellular matrix through the regulation of
endocytosis of the metalloproteinase MMP14 is associated with polarization
of the cells undergoing CE ( Williams et al., 2012 ). Collectively, these
suggest that the Wnt/PCP pathway mediates cell polarization underlying
CE by organizing extracellular matrices in between mesoderm cells and the
overlying ectoderm.
In a sheet of epithelia, basal lamina acts as a cue for apicobasal polarization.
However, little is known whether Fibronectin can provide with a basal input
into CE behavior of mesenchymal cells and how the apical complex
Par3-Par6-aPKC feeds into CE cell behavior. Par6 is required for CE
( Kusakabe & Nishida, 2004 ) and ArfGAP, which can form a complex with
Par6 and aPKC, mediates cell polarization underlying CE independently of
the Wnt/PCP pathway ( Hyodo-Miura et al., 2006 ). In contrast, Par1, which
is known to localize mutually exclusive to the apical complex in several dif-
ferent contexts, regulates CE by mediating Dsh phosphorylation ( Kusakabe &
Nishida, 2004; Ossipova et al., 2005 ). Par6 can form a complex with
Wnt5-mediated phosphorylated Dvl2 and the ubiquitin ligase Smurf,
which in turn targets Pk for degradation ( Narimatsu et al., 2009 ). In
addition, smurf1;smurf2 double mutants and embryos expressing a mutant
form of Par6 lacking a Dvl2-binding domain both exhibit severe CE
defects in mice ( Narimatsu et al., 2009 ). Together, the mediators of
apicobasal polarity and PCP feed in regulating cell polarization
independently but can cooperate to mediate CE behavior. It remains to be
investigated how these two pathways orchestrate coordinated cell movements.
5.4. Tissue elongation and oriented cell division
In addition to oriented cell interaction (CE), oriented cell division can
account for the elongation of a tissue. Indeed, the Wnt/PCP pathway
mediates cell division oriented in the AP axis of the epiblast/neural plate
in zebrafish ( Gong et al., 2004 ; Quesada-Hernandez et al., 2010 ). How does
the Wnt/PCP pathway regulate oriented cell division? NuMA, a protein
associated with nuclear mitotic apparatus, colocalizes with Dvl2 at the cleav-
age plane of a diving cell and controls mitotic spindle orientation in epiblast
cells, and acts downstream of the Wnt/PCP pathway in zebrafish ( Segalen
et al., 2010 ). The Fat-Ds pathway has also been implicated in the regulation