Cell surface proteoglycan that bears heparan sulfate. Regulates non-canonical Wnt signaling, being necessary and sufficient for fibronectrin-mediated translocation of dvl2/dsh to the plasma membrane. Required for proper convergent extension movements during gastrulation, which shape the neural plate, and for subsequent neural tube closure. Interacts with the Wnt receptor fzd7 and its signal transducer dvl2/dsh. Expressed in the animal hemisphere from the 4-cell to the blastula stage. During gastrulation, expressed in the involuting dorsal mesoderm and ectoderm. After involution, localized mainly to the anterior neuroectoderm. At later stages, expressed in the brain, branchial arches, pronephros, tailbud, and at low levels in the somites. Expressed both maternally and zygotically. Belongs to the syndecan proteoglycan family.