title: Identification of a rudimentary neural crest in a non-vertebrate chordate.
abstract: Neural crest arises at the neural plate border, expresses a core set of regulatory genes and produces a diverse array of cell types, including ectomesenchyme derivatives that elaborate the vertebrate head. The evolution of neural crest has been proposed to be a key event leading to the appearance of new cell types that fostered the transition from filter feeding to active predation in ancestral vertebrates. However, the origin of neural crest remains controversial, as homologous cell types have not been unambiguously identified in non-vertebrate chordates. Here we show that the tunicate Ciona intestinalis possesses a cephalic melanocyte lineage (a9.49) similar to neural crest that can be reprogrammed into migrating 'ectomesenchyme' by the targeted misexpression of Twist (also known as twist-like 2). Our results suggest that the neural crest melanocyte regulatory network pre-dated the divergence of tunicates and vertebrates. We propose that the co-option of mesenchyme determinants, such as Twist, into the neural plate ectoderm was crucial to the emergence of the vertebrate 'new head'.
authors.affiliation: Center for Integrative Genomics, Division of Genetics, Genomics and Development, Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: Philip Barron
authors.initials: PB
authors.lastname: Abitua
authors.forename: Eileen
authors.initials: E
authors.lastname: Wagner
authors.forename: Ignacio A
authors.initials: IA
authors.lastname: Navarrete
authors.forename: Michael
authors.initials: M
authors.lastname: Levine
mesh_terms: D000818:Animals; D019070:Cell Lineage; D002465:Cell Movement; D002938:Ciona intestinalis / Q000033:anatomy & histology* / Q000166:cytology / Q000196:embryology* / Q000235:genetics; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D054262:Gastrulation; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018878:Limb Buds / Q000196:embryology / Q000378:metabolism; D051739:Microphthalmia-Associated Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009432:Neural Crest / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D054258:Neural Plate / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D010802:Phylogeny; D051879:Twist-Related Protein 1 / Q000235:genetics / Q000378:metabolism; D060449:Wnt Signaling Pathway
chemical_list: D051858:Forkhead Transcription Factors; D051739:Microphthalmia-Associated Transcription Factor; D051879:Twist-Related Protein 1