Social Amoebae Linked by Nanotube Connections

Social amoebae are unicellular organisms that act in concert, requiring extensive communication. Pierre Stallforth and colleagues studied modes of communication among cells of the social amoeba Dictyostelium discoideum, using fluorescent labeling and various imaging techniques. The authors found that, in addition to signaling molecules drifting from cell to cell freely or inside membrane vesicles, the amoebae also create tunneling nanotubes that physically connect the membranes of cells. These actin-rich protrusions allow the transfer of cytoplasmic components and organelles over distances up to 100 μm. Such connections are found in multicellular organisms and metazoans, but previously unknown in social unicellular lineages. The nanotubes continue to function in cytoskeleton-perturbed conditions, which the authors induced with actin-depolymerizing agents, highlighting their importance to the organisms. The authors found various types of nanotubes, including branched forms connecting more than two cells. The protrusions were also occasionally seen connecting two different species of amoebae. According to the authors, tunneling nanotube connections could have played a role in the evolution of multicellularity, as intercellular communication is one of the most important traits driving this transition.