Homodimer; disulfide-linked. Expression is correlated temporally and spatially with somitogenesis. At late gastrula stage, expressed in the posterior presumptive neural plate. During somitogenesis, expression becomes restricted along the dorsoventral axis of the trunk neural tube in an anterior-to-posterior progression so that upon completion of somitogenesis, expression is seen exclusively in the ventral spinal cord with the exclusion of the floor plate and adjacent neural cells. By shh. Belongs to the TGF-beta family.