Giving neural precursors the finger

Epithelial cells communicate amongst themselves using finger-like projections, according to Cyrille de Joussineau, Daniel Alexandre, and colleagues (Université Montpellier II, Montpellier, France). The filopodia help individual fly neural precursors to create an island of nonneural cells around themselves, thus allowing the formation of discrete structures such as bristles at regular intervals.

The filopodia only become visible when single cells are labeled. Their inhibitory action is mediated by Delta attached to the filopodia, which contacts membrane-bound Notch on the surrounding, inhibited cells. The extent of visible filopodia roughly matched the range of inhibition. And overexpression of Delta increased the range of the filopodia, so Delta actually promotes formation of its own means of transport.

Inhibition of filopodial outgrowth did not prevent local Delta–Notch signaling, but did shut down longer range inhibition. The result was an increased density...