Mothers against decapentaplegic homolog 6

SMAD6 or mothers against decapentaplegic homolog 6 is a polypeptide that, as its name describes, is a homolog of the Drosophila gene "mothers against decapentaplegic". It belongs to the SMAD family of proteins, which belong to the TGFβ superfamily of modulators. Like many other TGFβ family members SMAD6 is involved in cell signalling. It acts as a regulator of TGFβ family (such as bone morphogenetic proteins) activity by competing with SMAD4 and preventing the transcription of SMAD4's gene products. There are two known isoforms of this protein.

Nomenclature
The SMAD proteins are homologs of both the drosophila protein, mothers against decapentaplegic (MAD) and the C. elegans protein SMA. The name is a combination of the two. During Drosophila research, it was found that a mutation in the gene, MAD, in the mother, repressed the gene, decapentaplegic, in the embryo. The phrase "Mothers against" was added since mothers often form organizations opposing various issues eg. Mothers Against Drunk Driving or (MADD).