This gene encodes a member of a family of proteins that act as downstream effectors of the bone morphogenetic protein (BMP) signaling pathway. The encoded protein is phosphorylated by BMP receptors, which stimulates its binding to SMAD4 and translocation into the nucleus, where it functions as a regulator of transcription. Activity of this protein is important for embryonic development. Mutation of this gene results in defects in pulmonary vasculature. [provided by RefSeq, Mar 2013]