Communicating by touch – neurons are not alone

• Cytonemes synapse with cells they target for signal exchange.
• Signal exchange in cytoneme, axonal and dendritic synapses is analogous.
• Contact-dependent signal exchange is not unique to neurons.

Long-distance cell–cell communication is essential for organ development and function. Whereas neurons communicate at long distances by transferring signals at sites of direct contact (i.e., at synapses), it has been presumed that the only way other cell types signal is by dispersing signals through extracellular fluid – indirectly. Recent evidence from Drosophila suggests that non-neuronal cells also exchange signaling proteins at sites of direct contact, even when long distances separate the cells. We review here contact-mediated signaling in neurons and discuss how this signaling mechanism is shared by other cell types.