The Role of Arrestins in Development - Progress in Molecular Biology and Translational Science - page 225

Canonical Wnt signaling
( Xenopus )

Non canonical Wnt signaling
( Xenopus )

Wnt11

Fzd11

P

P

P

CK1/2

A rrestin
Axin

Arrestin P

Dvl

P

Dvl

Arrestin

Dvl

GRK5

CK1/2

β cat

β cat

Rac RhoA

β cat

β cat

β cat

JNK

β cat

TCF

CE movements

Figure 9.2 b-Arrestin 2 and vertebrate Wnt signaling. barr2 is a regulator of both
canonical (left panel) as well as noncanonical (right panel) Wnt signaling. The studies
summarized in this model were mostly conducted in Xenopus. Other evidence origi-
nates from experiments using barr KO MEFs.

panel). During gastrulation, arr2 is expressed in cells of the dorsal marginal

zone (DMZ) of Xenopus embryos. 15 This is a group of cells that undergoes
extensive convergence and extension (CE) movements, during which cells
from lateral parts of the embryo move toward the midline. 65 At the midline,
they intercalate, by which a change in cell shape is induced and the
anterior-posterior axis becomes longer through this process. This elonga-
tion persists during the following neurulation and organogenesis stages,
when

b

arr2 is expressed in presumptive neural tissues. 15 At later stages, it
becomes localized to the brain, retina, the branchial arches, and the otic
vesicle. 15
The molecular basis for CE movements was first investigated in inver-
tebrates. It depends on the PCP pathway, 66,67 which in vertebrates is anal-
ogous to noncanonical Wnt/JNK signaling. MO-mediated knockdown
of

b

b arr2 in Xenopus interferes with this pathway, as embryos with reduced

b arr2 expression are shorter than wild-type embryos and display a bent

body curvature. 15 Strikingly, ectopic expression of b arr2 induces the same