title: Retracing the path of planar cell polarity.
abstract: BACKGROUND
  The Planar Cell Polarity pathway (PCP) has been described as the main feature involved in patterning cell orientation in bilaterian tissues. Recently, a similar phenomenon was revealed in cnidarians, in which the inhibition of this pathway results in the absence of cilia orientation in larvae, consequently proving the functional conservation of PCP signaling between Cnidaria and Bilateria. Nevertheless, despite the growing accumulation of databases concerning basal lineages of metazoans, very few information concerning the existence of PCP components have been gathered outside of Bilateria and Cnidaria. Thus, the origin of this module or its prevalence in early emerging metazoans has yet to be elucidated.
  
  
  RESULTS
  The present study addresses this question by investigating the genomes and transcriptomes from all poriferan lineages in addition to Trichoplax (Placozoa) and Mnemiopsis (Ctenophora) genomes for the presence of the core components of this pathway. Our results confirm that several PCP components are metazoan innovations. In addition, we show that all members of the PCP pathway, including a bona fide Strabismus ortholog (Van gogh), are retrieved only in one sponge lineage (Homoscleromorpha) out of four. This highly suggests that the full PCP pathway dates back at least to the emergence of homoscleromorph sponges. Consequently, several secondary gene losses would have occurred in the three other poriferan lineages including Amphimedon queenslandica (Demospongiae). Several proteins were not retrieved either in placozoans or ctenophores leading us to discuss the difficulties to predict orthologous proteins in basally branching animals. Finally, we reveal how the study of multigene families may be helpful to unravel the relationships at the base of the metazoan tree.
  
  
  CONCLUSIONS
  The PCP pathway antedates the radiation of Porifera and may have arisen in the last common ancestor of animals. Oscarella species now appear as key organisms to understand the ancestral function of PCP signaling and its potential links with Wnt pathways.
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale (IMBE UMR 7263), Aix Marseille Université, CNRS, IRD, Avignon Université, Station marine d'Endoume, Batterie des Lions, 13007, Marseille, France. quentin.schenkelaars@unige.ch.|Department of Genetics and Evolution, Institute of Genetics and Genomics in Geneva (IGe3), Faculty of Sciences, University of Geneva, Geneva, Switzerland. quentin.schenkelaars@unige.ch.
authors.forename: Quentin
authors.initials: Q
authors.lastname: Schenkelaars
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale (IMBE UMR 7263), Aix Marseille Université, CNRS, IRD, Avignon Université, Station marine d'Endoume, Batterie des Lions, 13007, Marseille, France.
authors.forename: Laura
authors.initials: L
authors.lastname: Fierro-Constain
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale (IMBE UMR 7263), Aix Marseille Université, CNRS, IRD, Avignon Université, Station marine d'Endoume, Batterie des Lions, 13007, Marseille, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Renard
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale (IMBE UMR 7263), Aix Marseille Université, CNRS, IRD, Avignon Université, Station marine d'Endoume, Batterie des Lions, 13007, Marseille, France. carole.borchiellini@imbe.fr.|Department of Genetics and Evolution, Institute of Genetics and Genomics in Geneva (IGe3), Faculty of Sciences, University of Geneva, Geneva, Switzerland. carole.borchiellini@imbe.fr.
authors.forename: Carole
authors.initials: C
authors.lastname: Borchiellini
mesh_terms: D000818:Animals; D016764:Cell Polarity; D003063:Cnidaria / Q000235:genetics; D037302:Ctenophora / Q000235:genetics; D004330:Drosophila / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D016678:Genome; D010802:Phylogeny; D011161:Porifera / Q000145:classification / Q000166:cytology* / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D059467:Transcriptome
keywords: Ctenophora; Metazoan phylogeny; Multigene families; Placozoa; Planar cell polarity; Porifera; Van Gogh; Wnt signaling