The Divergent Caenorhabditis elegans ß-Catenin Proteins BAR-1, WRM-1 and HMP-2 Make Distinct Protein Interactions but Retain Functional Redundancy in Vivo

Corresponding author: David M. Eisenmann, Department of Biological Sciences, University of Maryland, Baltimore County, 1000 Hilltop Cir., Baltimore, MD 21250., eisenman{at}umbc.edu (E-mail)

Communicating editor: B. J. MEYER

ß-Catenins function both in cell adhesion as part of the cadherin/catenin complex and in Wnt signal transduction as transcription factors. Vertebrates express two related proteins, ß-catenin and plakoglobin, while Drosophila has a single family member, Armadillo. Caenorhabditis elegans expresses three ß-catenin-related proteins, BAR-1, HMP-2, and WRM-1, which are quite diverged in sequence from each other and other ß-catenins. While BAR-1 and WRM-1 are known to act in Wnt-mediated processes, and HMP-2 acts in a complex with cadherin/-catenin homologs, it is unclear whether all three proteins retain the other functions of ß-catenin. Here we show that BAR-1, like vertebrate ß-catenin, has redundant transcription activation domains in its amino- and carboxyl-terminal regions but that HMP-2 and WRM-1 also possess the ability to activate transcription. We show via yeast two-hybrid analysis that these three proteins display distinct patterns of protein interactions. Surprisingly, we find that both WRM-1 and HMP-2 can substitute for BAR-1 in C. elegans when expressed from the bar-1 promoter. Therefore, although their mutant phenotypes and protein interaction patterns strongly suggest that the functions of ß-catenin in other species have been segregated among three diverged proteins in C. elegans, these proteins still retain sufficient similarity to display functional redundancy in vivo.

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