Cytoneme
Cytonemes are thin, cellular projections that are specialized for exchange of signaling proteins between cells. Cytonemes emanate from cells that make signaling proteins, extending directly to cells that receive signaling proteins. Cytonemes also extend directly from cells that receive signaling proteins to cells that make them. A cytoneme is a type of filopodium - a thin, tubular extension of a cell’s plasma membrane that has a core composed of tightly bundled, parallel actin filaments. Filopodia can extend more than 100 μm and have been measured as thin as 0.1 μm and as thick as 0.5 μm. Cytonemes with a diameter of approximately 0.2 μm and as long as 80 μm have been observed in the Drosophila wing imaginal disc. Many cell types have filopodia. The functions of filopodia have been attributed to pathfinding of neurons, early stages of synapse formation, antigen presentation by dendritic cells of the immune system, force generation by macrophages and virus transmission. They have been associated with wound closure, dorsal closure of Drosophila embryos, chemotaxis in Dictyostelium, Delta-Notch signaling, vasculogenesis, cell adhesion, cell migration, and cancer metastasis. Filopodia have been given various names: microspikes, pseudopods, thin filopodia, thick filopodia, gliopodia, myopodia, invadopodia, podosomes, telopodes, tunneling nanotubes