Appears to regulate cell differentiation within the neural tube. May regulate the differentiation of cell types along the dorsoventral axis of the neural tube, acting in conjunction with distinct ventralizing signals from the notochord and floor plate. Controls the cell differentiation in the neural tube in several ways: (1) promotes the differentiation of cell types that derive from the dorsal neural tube. (2) ensures that the dorsal neural tube is refractory to ventralizing species from the notochord. (3) can diffuse and influence the fate of cells in more ventral regions of the neural tube. Homodimer; disulfide-linked. Expressed selectively in the dorsal neural tube. Lower levels seen in kidney and myotomal cells. Is not expressed in neural cells at stages before neural tube closure. Is expressed at high levels in the dorsal third of the neural tube, beginning at the time of neural tube closure, but not by ventral neural cells or by nonneural cells. Dorsal restriction persists in the spinal cord at stages after the onset of neuronal differentiation. At later stages of spinal development, is restricted to the dorsomedial region of the spinal cord, including but not confined to the roof plate. Belongs to the TGF-beta family.