In mammalian embryos, the middle-ear chamber starts as a pouch that pokes out from the oral cavity. The roof of this cavity ruptures and fills with cells that then retract up over the bones of the middle ear, leaving an air-filled space.

Hannah Thompson and Abigail Tucker at King's College London looked at mice genetically engineered such that the descendants of cells in the developing ear could be tracked. This revealed a double origin for the epithelial cells within the cavity, and thus in two cell types. Cells lining the bottom of the cavity are thick and have cilia that robustly sweep away debris. Cells lining the roof are flat and offer little protection from debris or inflammation. The way in which the mammalian ear develops and our susceptibility to middle-ear infections may be related, the authors suggest.

Science 339, 1453–1456 (2013)