Mothers against decapentaplegic homolog 9 also known asSMAD9,SMAD8, andMADH6 is aprotein that in humans is encoded by theSMAD9 gene.[5]
SMAD9, as its name describes, is a homolog of theDrosophila gene: "Mothers against decapentaplegic". It belongs to theSMAD family of proteins, which belong to theTGFβ superfamily of modulators. Like many other TGFβ family members, SMAD9 is involved incell signalling. When abone morphogenetic protein binds to a receptor (BMP type 1 receptor kinase) it causes SMAD9 to interact withSMAD anchor for receptor activation (SARA).The binding of ligands causes thephosphorylation of the SMAD9 protein and the dissociation from SARA and the association withSMAD4. It is subsequently transferred to thenucleus where it forms complexes with other proteins and acts as atranscription factor. SMAD9 is areceptor regulated SMAD (R-SMAD) and is activated by bone morphogenetic protein type 1 receptor kinase. There are twoisoforms of the protein. Confusingly, it is also sometimes referred to as SMAD8 in the literature.
The SMAD proteins are homologs of both the drosophila protein, mothers against decapentaplegic (MAD) and theC. elegans protein SMA. The name is a combination of the two. DuringDrosophila 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 e.g.Mothers Against Drunk Driving or (MADD); and based on a tradition of such unusual naming within the gene research community.[6]
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