An F-Box/WD40 Repeat-Containing Protein Important for Dictyostelium Cell-Type Proportioning, Slug Behaviour, and Culmination

Abstract FbxA is a novel member of a family of proteins that contain an F-box and WD40 repeats and that target specific proteins for degradation via proteasomes. In fruiting bodies formed from cells where the fbxA gene is disrupted ( fbxA − cells), the spore mass fails to fully ascend the stalk. In addition, fbxA − slugs continue to migrate under environmental conditions where the parental strain immediately forms fruiting bodies. Consistent with this latter behaviour, the development of fbxA − cells is hypersensitive to ammonia, the signaling molecule that regulates the transition from the slug stage to terminal differentiation. The slug comprises an anterior prestalk region and a posterior prespore region and the fbxA mRNA is highly enriched in the prestalk cells. The prestalk zone of the slug is further subdivided into an anterior pstA region and a posterior pstO region. In fbxA − slugs the pstO region is reduced in size and the prespore region is proportionately expanded. Our results indicate that FbxA is part of a regulatory pathway that controls cell fate decisions and spatial patterning via regulated protein degradation.