Scientists at the Washington University School of Medicine in St. Louis have discovered a new link between two key proteins that regulate the placement of cell parts. Special placement of the various parts of a cell — a phenomenon scientists call cellular polarity — is essential for many life-sustaining functions. During development, moving parts to a particular region of a cell allows that region to become specialized when the cell divides. In a mature organism, cellular polarity allows a single cell to develop sides with multiple functions. For example, a cell that is part of an organ will develop different specialized properties on its sides that abut other organ cells (known to scientists as the basolateral surfaces) than on the sides of the cell that face the organ’s exterior or cavities (known as the apical surfaces).