Parallel duplication and partial subfunctionalization of β-catenin/armadillo during insect evolution.

β-Catenin is a multifunctional scaffolding protein with roles in Wnt signaling, cell adhesion, and centrosome separation. Here, we report on independent duplications of the insect β-Catenin ortholog armadillo (arm) in the red flour beetle Tribolium castaneum and the pea aphid Acyrthosiphon pisum. Detailed sequence analysis shows that in both species, one paralog lost critical residues of the α-Catenin binding domain, which is essential for cell adhesion, and accumulated a dramatically higher number of amino acid substitutions in the central Arm repeat domain. Residues associated with aspects of Wnt signaling, however, are conserved in both paralogs. Consistent with these molecular signatures, the effects of specific and combinatorial knockdown experiments in the Tribolium embryo indicate that the duplication resulted in redundant involvement in Wnt signaling of both β-Catenin paralogs but differential inheritance of the ancestral cell adhesion and centrosome separation functions. We conclude that the duplicated pea aphid and flour beetle β-catenin genes experienced partial subfunctionalization, which appears to be evolutionarily favored. Providing first evidence of genetic separability of the cell adhesion and centrosome separation functions, the duplicated Tribolium and Acyrthosiphon arm paralogs offer new inroads for context-specific analyses of β-Catenin. Our data also revealed the conservation of a C-terminally truncated Arm isoform in both singleton and duplicated homologs, suggesting an as yet unexplored role in Wnt signaling.