Cytonemes and tunneling nanotubules in cell–cell communication and viral pathogenesis

Cells use a variety of intercellular structures, including gap junctions and synapses, for cell–cell communication. Here, we present recent advances in the understanding of thin membrane bridges that function in cell–cell signaling and intercellular transport. Cytonemes or filopodial bridges connect neighboring cells via mechanisms of adhesion, which enable ligand-receptor-mediated transfer of surface-associated cargoes from cell to cell. By contrast, tunneling nanotubes establish tubular conduits between cells that provide for the exchange of both cell-surface molecules and cytoplasmic content. We propose models for the biogenesis of both types of membrane bridges and describe how viruses use these structures for the purpose of cell-to-cell spread.