title: Comparative transcriptome analysis between planarian Dugesia japonica and other platyhelminth species.
abstract: BACKGROUND
  Planarians are considered to be among the extant animals close to one of the earliest groups of organisms that acquired a central nervous system (CNS) during evolution. Planarians have a bilobed brain with nine lateral branches from which a variety of external signals are projected into different portions of the main lobes. Various interneurons process different signals to regulate behavior and learning/memory. Furthermore, planarians have robust regenerative ability and are attracting attention as a new model organism for the study of regeneration. Here we conducted large-scale EST analysis of the head region of the planarian Dugesia japonica to construct a database of the head-region transcriptome, and then performed comparative analyses among related species.
  
  
  RESULTS
  A total of 54,752 high-quality EST reads were obtained from a head library of the planarian Dugesia japonica, and 13,167 unigene sequences were produced by de novo assembly. A new method devised here revealed that proteins related to metabolism and defense mechanisms have high flexibility of amino-acid substitutions within the planarian family. Eight-two CNS-development genes were found in the planarian (cf. C. elegans 3; chicken 129). Comparative analysis revealed that 91% of the planarian CNS-development genes could be mapped onto the schistosome genome, but one-third of these shared genes were not expressed in the schistosome.
  
  
  CONCLUSIONS
  We constructed a database that is a useful resource for comparative planarian transcriptome studies. Analysis comparing homologous genes between two planarian species showed that the potential of genes is important for accumulation of amino-acid substitutions. The presence of many CNS-development genes in our database supports the notion that the planarian has a fundamental brain with regard to evolution and development at not only the morphological/functional, but also the genomic, level. In addition, our results indicate that the planarian CNS-development genes already existed before the divergence of planarians and schistosomes from their common ancestor.
authors: Department of Biophysics and Global COE Program, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto, Japan.
authors: Osamu
authors: O
authors: Nishimura
authors: Yukako
authors: Y
authors: Hirao
authors: Hiroshi
authors: H
authors: Tarui
authors: Kiyokazu
authors: K
authors: Agata
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002490:Central Nervous System / Q000378:metabolism; D020224:Expressed Sequence Tags; D020869:Gene Expression Profiling; D049751:Genome, Helminth / Q000235:genetics*; D010932:Planarians / Q000235:genetics*; D010986:Platyhelminths / Q000235:genetics*; D017422:Sequence Analysis, DNA