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Figure 5.1 The four main cell junctional classes from apex to base are the (1) adherens
junctions, which serve as actin anchors; (2) desmosomes, which serve as intermediate
filaments anchors; (3) tight junctions, which are selective permeability barriers; and (4)
gap junctions, which function as electrical and chemical couplers for adjacent cells.
Takeichi, 2009 ). In addition to these core components, a large number of
nonclassic cadherins and a recently identified IgG superfamily protein, the
nectins, are also localized in the adherens junctions ( Takai and Nakanishi,
2003; Takeichi, 2007 ).
Together, these components contribute to adherens junctions' major
roles in linking adjacent cells together and tethering the actin cytoskeleton
to the plasma membrane ( Drees et al., 2005; Yamada et al., 2005b ). Of the
cadherin superfamily in adherens junction, E-cadherin (epithelial cadherin)
has been extensively studied ( Angst et al., 2001; Hulpiau and van Roy,
2009 ). E-cadherin is essential for development, being first expressed as early
as the two-cell stage of mammalian embryos ( Larue et al., 1994;
Riethmacher et al., 1995; Torres et al., 1997 ), and in cancers, where its dys-
function has been implicated in tumor progression ( Takeichi, 1991 ). Of the
adherens junction armadillo proteins, b -catenin is known for its role in the
Wnt signaling pathway, which regulates cell-cell communications in devel-
opment (participating in embryonic patterning), as well as in various cell
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