Enables coreceptor activity. Acts upstream of or within several processes, including platelet-derived growth factor receptor signaling pathway; positive regulation of MAPK cascade; and ruffle assembly. Located in plasma membrane and ruffle. Is expressed in several structures, including brain; jaw; respiratory system; retina; and skeleton. Human ortholog(s) of this gene implicated in relapsing-remitting multiple sclerosis. Orthologous to human CSPG4 (chondroitin sulfate proteoglycan 4).