Loss of the β-catenin homologue aardvark causes ectopic stalk formation in Dictyostelium

Abstract

Aardvark (Aar) is a Dictyostelium β-catenin homologue with both cytoskeletal and signal transduction roles during development. Here, we show that loss of aar causes a novel phenotype where multiple stalks appear during late development. Ectopic stalks are preceded by misexpression of the stalk marker ST–lacZ in the surrounding tissue. This process does not involve the kinase GSK-3. Mixing experiments show that ectopic ST–lacZ expression and stalk formation are cell non-autonomous. The protein–cellulose matrix surrounding the stalk of aar mutant fruiting bodies is defective, and damage to the stalk of wild-type fruiting bodies leads to ectopic ST–lacZ expression. We postulate that poor synthesis of the stalk tube matrix allows diffusion of a stalk cell-inducing factor into the surrounding tissue.