title: Chordate roots of the vertebrate nervous system: expanding the molecular toolkit.
abstract: The vertebrate brain is highly complex with millions to billions of neurons. During development, the neural plate border region gives rise to the neural crest, cranial placodes and, in anamniotes, to Rohon-Beard sensory neurons, whereas the boundary region of the midbrain and hindbrain develops organizer properties. Comparisons of developmental gene expression and neuroanatomy between vertebrates and the basal chordate amphioxus, which has only thousands of neurons and lacks a neural crest, most placodes and a midbrain-hindbrain organizer, indicate that these vertebrate features were built on a foundation already present in the ancestral chordate. Recent advances in genomics have provided insights into the elaboration of the molecular toolkit at the invertebrate-vertebrate transition that may have facilitated the evolution of these vertebrate characteristics.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0202, USA. lzholland@ucsd.edu
authors.forename: Linda Z
authors.initials: LZ
authors.lastname: Holland
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000502:physiology; D002816:Chordata, Nonvertebrate / Q000033:anatomy & histology / Q000196:embryology / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D050437:Genes, Developmental; D006801:Humans; D009420:Nervous System / Q000166:cytology / Q000196:embryology / Q000254:growth & development; D009432:Neural Crest / Q000502:physiology; D014714:Vertebrates / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology