Origins of Bilateral Symmetry: Hox and Dpp Expression in a Sea Anemone

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Science  28 May 2004:
Vol. 304, Issue 5675, pp. 1335-1337
DOI: 10.1126/science.1091946


Over 99% of modern animals are members of the evolutionary lineage Bilateria. The evolutionary success of Bilateria is credited partly to the origin of bilateral symmetry. Although animals of the phylum Cnidaria are not within the Bilateria, some representatives, such as the sea anemone Nematostella vectensis, exhibit bilateral symmetry. We show that Nematostella uses homologous genes to achieve bilateral symmetry: Multiple Hox genes are expressed in a staggered fashion along its primary body axis, and the transforming growth factor–β gene decapentaplegic (dpp) is expressed in an asymmetric fashion about its secondary body axis. These data suggest that bilateral symmetry arose before the evolutionary split of Cnidaria and Bilateria.

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