title: Ascidians as excellent chordate models for studying the development of the nervous system during embryogenesis and metamorphosis.
abstract: The swimming larvae of the chordate ascidians possess a dorsal hollowed central nervous system (CNS), which is homologous to that of vertebrates. Despite the homology, the ascidian CNS consists of a countable number of cells. The simple nervous system of ascidians provides an excellent experimental system to study the developmental mechanisms of the chordate nervous system. The neural fate of the cells consisting of the ascidian CNS is determined in both autonomous and non-autonomous fashion during the cleavage stage. The ascidian neural plate performs the morphogenetic movement of neural tube closure that resembles that in vertebrate neural tube formation. Following neurulation, the CNS is separated into five distinct regions, whose homology with the regions of vertebrate CNS has been discussed. Following their larval stage, ascidians undergo a metamorphosis and become sessile adults. The metamorphosis is completed quickly, and therefore the metamorphosis of ascidians is a good experimental system to observe the reorganization of the CNS during metamorphosis. A recent study has shown that the major parts of the larval CNS remain after the metamorphosis to form the adult CNS. In contrast to such a conserved manner of CNS reorganization, most larval neurons disappear during metamorphosis. The larval glial cells in the CNS are the major source for the formation of the adult CNS, and some of the glial cells produce adult neurons.
authors.affiliation: Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka, 415-0025, Japan. sasakura@kurofune.shimoda.tsukuba.ac.jp
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Sasakura
authors.forename: Kaoru
authors.initials: K
authors.lastname: Mita
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Ogura
authors.forename: Takeo
authors.initials: T
authors.lastname: Horie
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D019521:Body Patterning; D002454:Cell Differentiation; D019070:Cell Lineage; D002938:Ciona intestinalis / Q000196:embryology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D047108:Embryonic Development; D018398:Homeodomain Proteins / Q000502:physiology; D008675:Metamorphosis, Biological; D009420:Nervous System / Q000166:cytology / Q000196:embryology / Q000254:growth & development*; D058953:Neural Stem Cells / Q000166:cytology / Q000502:physiology; D054259:Neural Tube / Q000166:cytology / Q000502:physiology; D009672:Notochord / Q000166:cytology / Q000502:physiology; D013550:Swimming / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology
chemical_list: D018398:Homeodomain Proteins; C111484:Hox 5 protein, Ciona intestinalis; D014157:Transcription Factors