Activated armadillo/beta-catenin does not play a general role in cell migration and process extension in Drosophila

Human beta -catenin and its fly homolog Armadillo are best known for their roles in cadherin-based cell-cell adhesion and in transduction of Wingless/ Wnt signals. It has been hypothesized that beta -catenin may also regulate cell migration and cell shape changes, possibly by regulating the microtubu le cytoskeleton via interactions with APC. This hypothesis was based on exp eriments in which a hyperstable mutant form of beta -catenin was expressed in MDCK cells, where it altered their migratory properties and their abilit y to send out long cellular processes. We tested the generality of this hyp othesis in vivo in Drosophila. We utilized three model systems in which cel l migration and/or process extension are known to play key roles during dev elopment: the migration of the border cells during oogenesis, the extension of axons in the nervous system, and the migration and cell process extensi on of tracheal cells. In all cases, cells expressing activated Armadillo we re able to migrate and extend cell processes essentially normally. The one alteration from normal involved an apparent cell fate change in certain tra cheal cells. These results suggest that only certain cells are affected by activation of armadillo/beta -catenin, and that Armadillo/beta -catenin doe s not play a general role in inhibiting cell migration or process extension . (C) 2001 Academic Press.