PerspectiveDevelopmental Biology

A Transition in the Middle Ear

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Science  22 Mar 2013:
Vol. 339, Issue 6126, pp. 1396-1397
DOI: 10.1126/science.1236645

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As a mammalian embryo develops, tubular tissues expand rapidly, often displacing resident mesenchymal cells, forming progressively enlarged areas such as the thoracic and abdominal cavities. Mechanistic explanations for such growth usually focus on cell proliferation and shape changes, or layering within the expanding tissue. On page 1453 of this issue, Thompson and Tucker (1) reveal that formation of the mammalian middle ear cavity is much more dynamic than thought, involving a programmed rupture of the epithelium and its replacement by a completely different cell type. In identifying two distinct origins of the cells that line the middle ear cavity, the authors overturn a long-held tenet of human embryology in suggesting that the process may be unique to mammals, perhaps in association with the evolution of the three middle ear sound-conducting bones.