Christian de Caestecker, a Ph.D. student in the lab of Ian Macara, Louise B. McGavock Professor and chair of the Department of Cell and Developmental Biology, has proposed and validated a mechanism that addresses a decades-old mystery surrounding epithelial cells. de Caestecker's research, published in Nature Cell Biology, sheds light on the process by which epithelial cells, polarized cells that face the outside world, sort and deliver the specialized proteins they need at each cell's top (outermost) surface.