Acts as an extracellular morphogen to establish at least two cellular response thresholds within the dorsal half of the drosophila embryo. Required for the proper development of the embryonic dorsal hypoderm, for viability of larvae and for cell viability of the epithelial cells in the imaginal disks. Acts together with scw (By similarity). Homodimer or heterodimer; disulfide-linked. Belongs to the TGF-beta family.