SIGNALING AND ADHESION ACTIVITIES OF MAMMALIAN BETA-CATENIN AND PLAKOGLOBIN IN DROSOPHILA

The armadillo protein of Drosophila and its vertebrate homologues, bet a-catenin and plakoglobin, are implicated in cell adhesion and wnt sig naling. Here, we examine the conservation of these two functions by as saying the activities of mammalian beta-catenin and plakoglobin in Dro sophila. We show that, in the female germ line, both mammalian beta-ca tenin and plakoglobin complement an armadillo mutation. We also show t hat shotgun mutant germ cells (which lack Drosophila E-cadherin) have a phenotype identical to that of armadillo mutant germ cells. It there fore appears that armadillo's role in the germ line is solely in a com plex with Drosophila E-cadherin (possibly an adhesion complex), and bo th beta-catenin and plakoglobin can function in Drosophila cadherin co mplexes. In embryonic signaling assays, we find that plakoglobin has n o detectable activity whereas beta-catenin's activity is weak. Surpris ingly, when overexpressed, either in embryos or in wing imaginal disks , both beta-catenin and plakoglobin have dominant negative activity on signaling, an effect also obtained with COOH-terminally truncated arm adillo. We suggest that the signaling complex, which has been shown by others to comprise armadillo and a member of the lymphocyte enhancer binding factor-1/T cell factor-family, may contain an additional facto r that normally binds to the COOH-terminal region of armadillo.