Cytonemes extend their reach

Thomas B Kornberg

Author Affiliations

  • Thomas B Kornberg, 1 Cardiovascular Research Institute, University of California, San Francisco, CA, USA

Cytonemes are specialized filopodia, first described in the Drosophila wing imaginal disc, that were proposed to mediate long distance signalling during development. A recent report from Barna and colleagues (Sanders et al, 2013) published in Nature shows that cytonemes in the chick limb bud carry SHH signalling proteins out to signal receiving cells, thus highlighting their evolutionarily conserved roles in cell–cell communication.

Our textbooks inform us that long distance signalling by animal cells is carried out in either of two ways. One, specific for neurons, involves signal exchange at sites of direct contact. The cell body of a neuron can be far from target cells (even metres away), but neurons extend processes that can bridge the distance to the target cell. Non‐neuronal cells, in contrast, are hemmed in by their neighbours, their contacts limited to nearest neighbours, and they use the other mode: signal release at the surface of signal‐producing cells, followed by dispersion in extracellular fluid so that released signals eventually bind to receptors on target cells.

This clean dichotomy of form and function that has long been thought to distinguish neurons from all other cells appears no longer valid. Several lines of evidence now show that non‐neuronal cells also extend asymmetric processes—filopodia—that mediate long‐range …

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