Enables Roundabout binding activity. Acts upstream of or within several processes, including axon guidance; nuclear migration; and tangential migration from the subventricular zone to the olfactory bulb. Located in extracellular space. Is expressed in several structures, including alimentary system; branchial arch; central nervous system; olfactory system; and retina. Orthologous to human SLIT1 (slit guidance ligand 1). [provided by Alliance of Genome Resources, Apr 2022]