368
Cell Junctions, Structure, Function, and Regulation
Claudin
Occludin
ZO-3
ZO-3
ZO-1
ZO-1
ZO-2
ZO-2
F-Actin
TJ
AJ
JAM
Nectin
Y
X
Afadin
a
-Actinin
a
-Actinin
a
-Catenin
b
-Catenin
Vinculin
F-Actin
bundles
123
EC
E-Cadherin
45
Matrix
Claudin
(b)
(a)
Claudin
Claudin
JAM
Nectin
Cadherin
JAM
JAM
Nectin
Cadherin
Cadherin
Nectin
(TJ)
(AJ)
Fig. 15
Model for the formation of adherens
and TJs. (a) Multiple proteins are localized to
mature adherens and TJs. Some proteins such as
ZO-1 can be found in both types of junctions and
have been proposed to serve as intermediates
allowing AJs to initiate tight junction formation.
(b) Filopodia from one cell contact an adjacent
cell allowing cadherins and nectins to cluster. As
the cadherin/nectin junction expands JAM is
incorporated, resulting in the localization of tight
junction proteins and the initiation of tight
junction formation. The tight junction matures
into a separate structure. (Reprinted with
permission from Takai, Y., Nakanishi, H. (2003)
Nectin and afadin: novel organizers of
intercellular junctions,
J. Cell Sci.
116
, 17–27).
proteins in this proposed model using
techniques such as siRNA (small interfer-
ing RNAs) will be critical in determining
the importance of the AJ to tight junction
assembly.
3
Summary and Future Directions
The interaction of cells with the ECM
and withone another plays an essential
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