Controls axon guidance across the CNS midline by preventing the delivery of Robo to the growth cone. Interacts (probably via PY-motifs) with Nedd4 (via WW2 domain) (PubMed:12165468, PubMed:16531238). Interacts with Robo (PubMed:12165468). The cytoplasmic domain is required for function in axon guidance. Ubiquitinated by Nedd4; which promotes endocytosis of the comm/robo complex and comm proteasomal degradation (PubMed:12165468). Not ubiquitinated by Nedd4 (PubMed:15657595). Belongs to the commissureless family.