title: Anteroposterior patterning in hemichordates and the origins of the chordate nervous system.
abstract: The 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.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA. clowe@uclink4.berkeley.edu
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lowe
authors.forename: Mike
authors.initials: M
authors.lastname: Wu
authors.forename: Adrian
authors.initials: A
authors.lastname: Salic
authors.forename: Louise
authors.initials: L
authors.lastname: Evans
authors.forename: Eric
authors.initials: E
authors.lastname: Lander
authors.forename: Nicole
authors.initials: N
authors.lastname: Stange-Thomann
authors.forename: Christian E
authors.initials: CE
authors.lastname: Gruber
authors.forename: John
authors.initials: J
authors.lastname: Gerhart
authors.forename: Marc
authors.initials: M
authors.lastname: Kirschner
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics*; D002816:Chordata, Nonvertebrate / Q000166:cytology / Q000196:embryology* / Q000235:genetics; D004475:Ectoderm / Q000166:cytology / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000196:embryology; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D005801:Genes, Homeobox / Q000235:genetics; D007448:Invertebrates / Q000196:embryology* / Q000378:metabolism; D008969:Molecular Sequence Data; D009420:Nervous System / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D010802:Phylogeny; D012689:Sequence Homology, Nucleic Acid; D014714:Vertebrates / Q000196:embryology* / Q000378:metabolism