Attractive and repulsive functions of Slit are mediated by different receptors in the Drosophila trachea.

Oxygen delivery in many animals is enabled by the formation of unicellular capillary tubes that penetrate target tissues to facilitate gas exchange. We show that the tortuous outgrowth of tracheal unicellular branches towards their target tissues is controlled by complex local interactions with target cells. Slit, a phylogenetically conserved axonal guidance signal, is expressed in several tracheal targets and is required both for attraction and repulsion of tracheal branches.