Development

Surprising Origins

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Science  21 Sep 2012:
Vol. 337, Issue 6101, pp. 1434
DOI: 10.1126/science.337.6101.1434-a
CREDIT: ISTOCKPHOTO/THINKSTOCK

Similarities exist between the inner ear hair cells of humans and the lateral line hair cells of fish. Both respond to mechanical movements, from sound waves or water, respectively, and both arise from placodes of head ectoderm during early development. Humans, however, do not have a lateral line sensory organ. Many amniotes, including birds and some reptiles, have a paratympanic organ (PTO) near the middle ear that similarly contains hair cells and responds to mechanical distortion, suggestive of an evolutionary linkage between the lateral line and the PTO. O'Neill et al. now show that these ideas are close to the mark, but not right on. Studying the PTO in chickens, the authors show that the PTO derives from an ectodermal placode close by, but distinct from, the placodes that generate geniculate neurons and the lateral line. Although the PTO and geniculate placodes are so close as to almost blend together, they are nonetheless distinguished by their patterns of transcription factor expression and the developmental progressions that follow. The authors suggest that the PTO placode represents its own developmental module, subject to evolutionary trajectories independent of those of the lateral line.

Nat. Commun. 3, 1041 (2012).

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