Functions as guanine nucleotide exchange factor for RAC1 (By similarity). Plays a role in semaphorin signaling via its interaction with PLXNA4. Plays a role in the assembly and disassembly of dendritic filopodia, the formation of dendritic spines, regulation of dendrite length and ultimately the formation of synapses. Interacts with PLXNA4. Detected in lateral motor column motor neurons and in preganglionic autonomic motor neurons of the column of Terni in the embryonic spinal cord (at protein level). Up-regulated by retinol. Intramolecular interaction between the DH domain and the PH domains can stabilize the protein in an autoinhibited conformation.