SPON1 is a member of a subgroup of the thrombospondin type 1 (TSR) class molecules, defined by two domains of homology, the FS1/FS2 and TSR domains. The TSRs of SPON1 proteins are typical of class 2 TSRs. SPON1, which is similar to thrombospondin, is a extracellular matrix attached molecule that promotes neurite outgrowth and inhibits angiogenesis. Analysis of gain and loss of function experiments reveal that SPON1 is required for accurate pathfinding of embryonic axons, and plays a dual role in patterning axonal trajectories. It promotes the outgrowth of commissural and inhibits the outgrowth of motor axons, and has also been implicated in inflammatory processes in the nervous system.