Activated proto-oncogene vav (VAV) act as guanine nucleotide exchange factors (GEFs) for RAC1, catalysing the exchange of bound GDP for GTP. Endocytosis of large EPH:EFN complexes is dependent on RAC1-regulated actin polymerisation. RAC1 signaling is positively linked to EPH:EFN internalization but the exact link to clathrin endocytosis machinery remains unclear. Inhibiting RAC1 signalling and Arp2/3-driven actin polymerization in EPH receptor-expressing cells completely blocks both endocytosis of EPH:EFN complexes and cell retraction (Marston et al. 2003). In response to repulsive guidance molecules, the function of RAC1 changes from promoting actin polymerization associated with axon growth to driving endocytosis of the plasma membrane, resulting in growth cone collapse (Jurney et al. 2002).