title: The nervous system of Xenacoelomorpha: a genomic perspective.
abstract: Xenacoelomorpha is, most probably, a monophyletic group that includes three clades: Acoela, Nemertodermatida and Xenoturbellida. The group still has contentious phylogenetic affinities; though most authors place it as the sister group of the remaining bilaterians, some would include it as a fourth phylum within the Deuterostomia. Over the past few years, our group, along with others, has undertaken a systematic study of the microscopic anatomy of these worms; our main aim is to understand the structure and development of the nervous system. This research plan has been aided by the use of molecular/developmental tools, the most important of which has been the sequencing of the complete genomes and transcriptomes of different members of the three clades. The data obtained has been used to analyse the evolutionary history of gene families and to study their expression patterns during development, in both space and time. A major focus of our research is the origin of 'cephalized' (centralized) nervous systems. How complex brains are assembled from simpler neuronal arrays has been a matter of intense debate for at least 100 years. We are now tackling this issue using Xenacoelomorpha models. These represent an ideal system for this work because the members of the three clades have nervous systems with different degrees of cephalization; from the relatively simple sub-epithelial net of Xenoturbella to the compact brain of acoels. How this process of 'progressive' cephalization is reflected in the genomes or transcriptomes of these three groups of animals is the subject of this paper.
authors.affiliation: Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Perea-Atienza
authors.affiliation: Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain.
authors.forename: Brenda
authors.initials: B
authors.lastname: Gavilán
authors.affiliation: Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Chiodin
authors.affiliation: Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain Institut de Biomedicina de la Universitat de Barcelona (IBUB), Av. Diagonal, 643, 08028 Barcelona, Catalonia, Spain.
authors.forename: Josep F
authors.initials: JF
authors.lastname: Abril
authors.affiliation: Ernst Morith Arndt University of Greifswald, Institute for Mathematics and Computer Science, Walther-Rathenau-Str. 47, 17487 Greifswald, Germany.
authors.forename: Katharina J
authors.initials: KJ
authors.lastname: Hoff
authors.affiliation: Dahlem Centre for Genome Research and Medical Systems Biology, Evolutionary and Environmental Genomics Group, Fabeckstraße 60-62, 14195 Berlin, Germany.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Poustka
authors.affiliation: Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys, 23 08010 Barcelona, Catalonia, Spain Pedro.martinez@ub.edu.
authors.forename: Pedro
authors.initials: P
authors.lastname: Martinez
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016678:Genome; D007448:Invertebrates / Q000033:anatomy & histology / Q000145:classification* / Q000235:genetics; D008969:Molecular Sequence Data; D009420:Nervous System / Q000033:anatomy & histology*; D010802:Phylogeny; D010986:Platyhelminths / Q000033:anatomy & histology / Q000145:classification
keywords: Acoela; Acoelomorpha; Evolution; GPCR; Neural system; Symsagittifera; Xenoturbella; bHLH; cephalization