Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
???displayArticle.abstract???
Wnt genes encode secreted glycoproteins, and, because of their homology with the Drosophila segment polarity gene wingless, are likely to play important roles as modulators of local intercellular signalling during embryonic development. Although little is known of the mechanisms by which Wnts signal in an autocrine or paracrine manner, it is increasingly clear that cells can respond rapidly to Wnt signals in the absence of transcription, and that these responses may include changes in cell adhesion and cell movement. We review recent evidence from studies on Xenopus laevis and other systems, which demonstrate that (1) a subset of Wnts modulate gap junctional permeability, which may be a reflection of changes in cadherin-mediated cell adhesion, (2) embryos express beta-catenin and plakoglobin, which are homologs of the armadillo gene products, known to be involved in the wingless signalling pathway, and known to be found at cell junctions, and (3) overexpression of specific Wnts in Xenopus embryos leads to clear changes in cell behavior and movement.
Fig. 1. Overlapping expression of A\vni-3A, Xwnt-1 and P-catenin
transcripts in the Xenopus tadpole. Whole mount in situ
hybridization was conducted for Xwnt-3A (left panel in (A)),
Xwnt- 1 (right panel in (A); Wolda et al., 1993) or |3-catenin (B)
(DeMarais and Moon, 1992) transcripts, and tadpole embryos
were then sectioned transversely at the level shown in the cartoon.
The arrows denote the area of overlapping expression of these
transcripts in the mesencephalon (M)/prosencephalon (P)
boundary, with dorsal upwards in all panels. The eye (E) is
evident in the left panel in (A), and in (B). Bar in (A) is 50 |lm.
Fig. 2. Speculative model of Wnt signalling and
responses at cell junctions. Upon secretion of Wnt
from the colored cell, the Wnt may act in an
autocrine or paracrine manner via a receptormediated
signal transduction pathway, though at
present there is no direct evidence for a plasma
membrane-associated Wnt receptor. However, as
described in the text, there is now evidence
indicating that cells can respond to Wnt signals by
modulation of gap junctional permeability, and
that this effect may be an indirect consequence of
changes in cell adhesion. In addition, armadillo is
downstream of the Wnt- 1 signal in Drosophila,
and the armadillo homologs (3 catenin and
plakoglobin are associated with adherens
junctions in vertebrate cells, which contain
cadherins. Plakoglobin is also found at
desmosomes. Finally, as described in the text,
there is direct evidence that cells in Xenopus
embryos undergo changes in cell adhesion and
migration in response to Wnt signals.
