Thought to be involved during neural development in axonal navigation at the ventral midline of the neural tube (PubMed:15084255, PubMed:30843071). In spinal cord development plays a role in guiding commissural axons probably by preventing premature sensitivity to Slit proteins thus inhibiting Slit signaling through ROBO1 (PubMed:15084255). Required for hindbrain axon midline crossing (PubMed:30843071). Probably interacts with SLIT2. A number of isoforms are produced. Detected in embryonal spinal cord and hindbrain. At 10.5 dpc is expressed in long stripes in the dorso-ventral part of the neural tube. Later at 11.5, 12.5 and 13.5 dpc expression gradually moves dorsally and medially towards the roof plate. At 11.5 dpc highly expressed in spinal cord commissural exons before crossing the floor plate. After midline crossing initially continues to be expressed but then gets down-regulated. ROBO3 null deficient mice lack embryonal spinal chord commissural axons crossing the floor plate. The region from 1 to 53 was deduced from the genomic sequence and ESTs by similarity to the human sequence. Belongs to the immunoglobulin superfamily. ROBO family.