Mothers against decapentaplegic homolog 9

Mothers against decapentaplegic homolog 9 also known as SMAD9, SMAD8, and MADH6 is a is_associated_with::protein that in humans is enocoded by the SMAD9 gene.

SMAD9, as its name describes, is a homolog of the Drosophila gene: "is_associated_with::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, SMAD9 is involved in is_associated_with::cell signalling. When a is_associated_with::bone morphogenetic protein binds to a receptor (BMP type 1 receptor kinase) it causes SMAD9 to interact with is_associated_with::SMAD anchor for receptor activation (SARA).The binding of ligands causes the is_associated_with::phosphorylation of the SMAD9 protein and the dissociation from SARA and the association with is_associated_with::SMAD4. It is subsequently transferred to the nucleus where it forms complexes with other proteins and acts as a is_associated_with::transcription factor. SMAD9 is a receptor regulated SMAD (is_associated_with::R-SMAD) and is activated by bone morphogenetic protein type 1 receptor kinase. There are two is_associated_with::isoforms of the protein. Confusingly, it is also sometimes referred to as SMAD8 in the literature.

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, is_associated_with::decapentaplegic, in the embryo. The phrase "Mothers against" was added since mothers often form organizations opposing various issues e.g. is_associated_with::Mothers Against Drunk Driving or (MADD).