UNCOUPLING CADHERIN-BASED ADHESION FROM WINGLESS SIGNALING IN DROSOPHILA

THE Wnt genes encode secreted glycoproteins used in intercellular comm unication at multiple steps during development. Signalling by Wingless , the Drosophila Wnt-1 homologue, requires the activity of Armadillo(1 ,2), the homologue of vertebrate beta-catenin(3), which is a component of the cadherin/catenin complex at adherens junctions(4,5). The genet ic link between wingless and armadillo suggests that cell fate specifi cation and cell-cell adhesion might be controlled concurrently. For in stance, in one extreme view, Wingless could specify cell fate entirely by modulating cell adhesion. Alternatively, it might signal independe ntly of adherens junctions. To distinguish between these alternatives, we have expressed two polypeptides that have opposite effects on cadh erin-dependent adhesion: full-length Drosophila E-cadherin and a domin ant-negative truncated form. We found that overexpression of either co nstruct mimics wingless phenotypes, thereby uncoupling changes in adhe sion from signalling effects. We demonstrate that both constructs titr ate Armadillo from a 'signalling' pool which is functionally distinct from the junctional pool.