Commissureless regulates Roundabout (Robo) levels and as a result regulates controls axon guidance across the embryo midline [1-2].

1: Drosophila Nedd4, a ubiquitin ligase, is recruited by Commissureless to control cell surface levels of the roundabout receptor. Myat A, Henry P, McCabe V, Flintoft L, Rotin D, Tear G; Neuron. 2002;35:447-459. PMID:12165468

2: Comm function in commissural axon guidance: cell-autonomous sorting of Robo in vivo. Keleman K, Ribeiro C, Dickson BJ; Nat Neurosci. 2005;8:156-163. PMID:15657595