Morphogen Pipeline Developmental effects of morphogens are often thought to result from release of such signaling proteins from a cell, which then diffuse away to act by binding to receptors on distant target cells. But evidence is accumulating that another mechanism exists for such communication. Endothelial cells in the fruit fly have long, skinny extensions that reach away from cells for long distances, and these “cytonemes” can take up morphogens from adjacent cells. A key experiment to support a signaling role of such structures would be to show that disruption of cytonemes disrupts signal transduction. Roy et al. (p. 10.1126/science.1244624 , published online 2 January; see the Perspective by Rørth ) provide such evidence and conclude that the fly morphogen known as decapentaplegic (a relative of transforming growth factor.β) must be transported through cytonemes to promote proper development of the trachea.