Separate and unequal Deltas

Among its many functions, the Notch pathway helps orchestrate the formation of somites that give rise to the vertebral column and other structures. The pathway appears to be full of redundancy. For example, mice carry four Notch genes and three for the Delta proteins that interact with the pathway. The jobs of two of the Delta proteins, DLL1 and DLL3, have remained unclear. Initial studies suggested that the proteins are interchangeable. But individually deleting the proteins, which are made in the same part of the mesoderm, induces different developmental defects, and a recent study suggested that DLL3 interferes with...