A fundamental question in cell biology is, how do cells control how strongly to stick to each other? Sometimes, cells need to be quite tightly glued together, for example in the lining of a blood vessel. At other times, they need to be able to peel apart. Understanding how cells can stick or unstick from each other is important for understanding tissue growth and wound healing. Cancers metastasize when tumor cells can come unstuck from a tumor and spread to other tissues.