title: Ancient deuterostome origins of vertebrate brain signalling centres.
abstract: Neuroectodermal signalling centres induce and pattern many novel vertebrate brain structures but are absent, or divergent, in invertebrate chordates. This has led to the idea that signalling-centre genetic programs were first assembled in stem vertebrates and potentially drove morphological innovations of the brain. However, this scenario presumes that extant cephalochordates accurately represent ancestral chordate characters, which has not been tested using close chordate outgroups. Here we report that genetic programs homologous to three vertebrate signalling centres-the anterior neural ridge, zona limitans intrathalamica and isthmic organizer-are present in the hemichordate Saccoglossus kowalevskii. Fgf8/17/18 (a single gene homologous to vertebrate Fgf8, Fgf17 and Fgf18), sfrp1/5, hh and wnt1 are expressed in vertebrate-like arrangements in hemichordate ectoderm, and homologous genetic mechanisms regulate ectodermal patterning in both animals. We propose that these genetic programs were components of an unexpectedly complex, ancient genetic regulatory scaffold for deuterostome body patterning that degenerated in amphioxus and ascidians, but was retained to pattern divergent structures in hemichordates and vertebrates.
authors.affiliation: Committee on Evolutionary Biology, The University of Chicago, 1025 East 57th Street, Chicago, Illinois 60637, USA.
authors.forename: Ariel M
authors.initials: AM
authors.lastname: Pani
authors.forename: Erin E
authors.initials: EE
authors.lastname: Mullarkey
authors.forename: Jochanan
authors.initials: J
authors.lastname: Aronowicz
authors.forename: Stavroula
authors.initials: S
authors.lastname: Assimacopoulos
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Grove
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lowe
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology* / Q000196:embryology* / Q000502:physiology; D043344:Chordata / Q000033:anatomy & histology* / Q000196:embryology* / Q000235:genetics / Q000502:physiology; D005346:Fibroblast Growth Factors / Q000378:metabolism; D053823:Hedgehog Proteins / Q000378:metabolism; D051379:Mice; D015398:Signal Transduction; D014714:Vertebrates / Q000033:anatomy & histology* / Q000196:embryology* / Q000235:genetics / Q000502:physiology; D060449:Wnt Signaling Pathway
chemical_list: D053823:Hedgehog Proteins; D005346:Fibroblast Growth Factors