The function of PP2A/B56 in non-metazoan multicellular development

DB56, the Dictyostelium B56 homolog, displayed high sequence homology to other eukaryotic B56 subunits of the PP2A and a specific association with the PP2A catalytic subunit. Cells lacking DB56, psrA−, displayed higher PP2A phosphatase activity compared with the wild type, ∼10 hr of delayed expression of ecmA and ecmB prestalk markers, and inefficient culmination. The prespore marker cotB declined as wild-type cells culminate, but no such decline was observed from psrA− cells. Interestingly, psrA− cells exhibited higher GSK3 kinase activity. Furthermore, the expression of the dominant negative GSK3 mutant (K84/85M) in psrA− cells improved both prestalk and prespore expression patterns similarly to wild-type cells. However, culmination was not restored in psrA− cells expressing dominant negative GSK3, which suggests that PP2A/DB56 has an extra target during terminal differentiation. This report shows that PP2A/DB56 controls not only metazoan development, but also non-metazoan cell fate decision processes.