A tremendous amount of genetics research has been done in flies and tiny worms, in part because scientists have good tools for tweaking these creatures’ DNA. Now, by adapting a powerful method of RNA interference for use in mice, researchers have identified key pathways that cause skin cells to differentiate, eventually forming the flexible but protective outer casing of the body. The work illustrates the potential for performing relatively fast and complex genetic studies in a fellow mammal, and also provides a deeper understanding of cell differentiation in early development.