Cytoneme

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.

Cytonemes take up and transport morphogens. This micrograph shows tissues from a Drosophila larva whose tracheal cells are marked with membrane-tethered mCherry fluorescent protein. Some of the cytonemes that extend from the tracheal branch contact the underlying wing imaginal disc and transport the Dpp morphogen protein (marked with green fluorescent protein) to the tracheal cells. [ citation needed ]