Cytonemes are thin, cellular projections that are specialized for exchange of signaling proteins between cells.
[1][3][4] 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.
[1] The term cytoneme was coined to denote the presence of cytoplasm in their interior (cyto-) and their finger-like appearance (-neme), and to distinguish their role as signaling, rather than structural or force-generating, organelles.
[6][7] The discovery of cytonemes in Drosophila imaginal discs[1] correlated for the first time the presence and behavior of filopodia with a known morphogen signaling protein - decapentaplegic.
[4] In Drosophila, cytonemes have been found in wing and eye imaginal discs,[3][10] trachea,[11][12] lymph glands[13] and ovaries.