0092-867411372003Jun27CellAnteroposterior patterning in hemichordates and the origins of the chordate nervous system.853865853-65The chordate central nervous system has been hypothesized to originate from either a dorsal centralized, or a ventral centralized, or a noncentralized nervous system of a deuterostome ancestor. In an effort to resolve these issues, we examined the hemichordate Saccoglossus kowalevskii and studied the expression of orthologs of genes that are involved in patterning the chordate central nervous system. All 22 orthologs studied are expressed in the ectoderm in an anteroposterior arrangement nearly identical to that found in chordates. Domain topography is conserved between hemichordates and chordates despite the fact that hemichordates have a diffuse nerve net, whereas chordates have a centralized system. We propose that the deuterostome ancestor may have had a diffuse nervous system, which was later centralized during the evolution of the chordate lineage.LoweChristopher JCJDepartment of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA. clowe@uclink4.berkeley.eduWuMikeMSalicAdrianAEvansLouiseLLanderEricEStange-ThomannNicoleNGruberChristian ECEGerhartJohnJKirschnerMarcMengGENBANKAY313137AY313138AY313139AY313140AY313141AY313142AY313143AY313144AY313145AY313146AY313147AY313148AY313149AY313150AY313151AY313153AY313154AY313155AY313157AY313158AY313159AY318740AY3187411-R01-HD42724HDNICHD NIH HHSUnited StatesJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.Research Support, U.S. Gov't, P.H.S.