Fig. 3.

Schematic representations of three distinct nanoscaled cellular protrusions and proposed modes of cell-to-cell communication. (a) A TNT-mediating membrane continuity between cells. (a₁) Organelles like endocytic vesicles and mitochondria are transported uni-directionally between cells by an actin-dependent mechanism. (b) Nanotubular bridge between cells displaying a junctional border. (b₁) Distinct viral particles are transported either at the surface of the nanotube by a receptor-dependent mechanism using actin retrograde flow or inside the cellular nanotube by an actin-dependent mechanism. (c) Cellular nanotube (cytoneme) extending toward a target cell by chemotaxis. (c₁) Signaling molecules secreted by the target cell are proposed to be endocytosed by a receptor-mediated mechanism at the tip of the cytoneme and transported in a retrograde manner toward the cell body of the receiving cell. The arrows (a–c) indicate the direction of transfer