SCO-Spondin is a large protein that exists in most chordates and is encoded in humans by the SSPO gene. SCO-Spondin is a glycoprotein which is over 550 kDa in size. SCO-Spondin is a matricellular protein, secreted by the subcommissural organ (SCO) located beneath the posterior commissure located at the entrance of the Sylvian aqueduct, into the cerebrospinal fluid (CSF). SCO-spondin has the binding features of an LDL-binding protein. SCO-spondin has been characterized in zebrafish, mouse, and birds.