Biomedical Engineering Reference
In-Depth Information
Planar cell polarity
Proximal
Distal
Fmi
Stbm, Pk
Fz, Dvl, Dgo
Figure 8.1 Schematic illustration of planar cell polarity (PCP). PCP is perpendicular to
the apico-basal polarity of the epithelial tissue. PCP proteins are asymmetrically local-
ized at the cell junctions between neighboring cells. This asymmetry defines the tissue
polarity.
localization of proteins, macromolecules, and organelles. Indeed, in some
tissues, many of the PCP determinants are themselves localized within
the plane of the cell and are required for the subcellular localization of other
pathway determinants (
Fig. 8.1
). For instance, during PCP establishment in
the fly wing, Fz and Dsh are localized on the distal side of the cell, while
Vang and Pk are localized on the proximal side (
Axelrod, 2001; Bastock,
Strutt, & Strutt, 2003; Das, Jenny, Klein, Eaton, & Mlodzik, 2004;
Jenny, Darken, Wilson, & Mlodzik, 2003; Shimada, Usui, Yanagawa,
Takeichi, & Uemura, 2001; Tree, Shulman, et al., 2002
). The precise
mechanisms regulating the planar-polarized positions of each protein are
still not perfectly clear although they appear to be reinforced by positive
and negative interactions with other core proteins. It is still not clear if the
polarized localization of the core or Fat/Ds determinants is maintained in
all vertebrate tissues manifesting PCP. Ultimately, the Fz/PCP and Ft/Ds
pathways regulate the polarization of
the cytoskeleton (
Tree, Ma, &
Axelrod, 2002
).
2.3. The Wnt pathway
Wnt ligands play a crucial role in establishing PCP in vertebrates. Wnts sig-
nal through an ever-expanding group of receptors and coreceptors
(
Buechling & Boutros, 2011
). Nearly all Wnt signaling depends on interac-
tion of the ligand with a Fz receptor. Note that this is the same Fz molecule
that is a component of the core PCP group. Dsh also appears to play a dual
