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, e.g., Mothers Against Drunk Driving, or (MADD). The nomenclature for this protein, like that of Sonic hedgehog, has been criticized for its frivolity
Read more about this topic: Mothers Against Decapentaplegic Homolog 2