The N-terminal predicted helical stretch of the insulin receptortyrosine kinase substrate p53 (IRSp53) is an evolutionaryconserved F-actin bundling domain involved in filopodiumformation. The domain has been named IMD after the IRSp53 andmissing in metastasis (MIM) proteins in which it occurs.Filopodium-inducing IMD activity is regulated by Cdc42 and Rac1and is SH3-independent [1]. IRSp53/MIM homology domain IMD