title: Comparative study of Hippo pathway genes in cellular conveyor belts of a ctenophore and a cnidarian.
abstract: BACKGROUND
  The Hippo pathway regulates growth rate and organ size in fly and mouse, notably through control of cell proliferation. Molecular interactions at the heart of this pathway are known to have originated in the unicellular ancestry of metazoans. They notably involve a cascade of phosphorylations triggered by the kinase Hippo, with subsequent nuclear to cytoplasmic shift of Yorkie localisation, preventing its binding to the transcription factor Scalloped, thereby silencing proliferation genes. There are few comparative expression data of Hippo pathway genes in non-model animal species and notably none in non-bilaterian phyla.
  
  
  RESULTS
  All core Hippo pathway genes could be retrieved from the ctenophore Pleurobrachia pileus and the hydrozoan cnidarian Clytia hemisphaerica, with the important exception of Yorkie in ctenophore. Expression study of the Hippo, Salvador and Scalloped genes in tentacle "cellular conveyor belts" of these two organisms revealed striking differences. In P. pileus, their transcripts were detected in areas where undifferentiated progenitors intensely proliferate and where expression of cyclins B and D was also seen. In C. hemisphaerica, these three genes and Yorkie are expressed not only in the proliferating but also in the differentiation zone of the tentacle bulb and in mature tentacle cells. However, using an antibody designed against the C. hemiphaerica Yorkie protein, we show in two distinct cell lineages of the medusa that Yorkie localisation is predominantly nuclear in areas of active cell proliferation and mainly cytoplasmic elsewhere.
  
  
  CONCLUSIONS
  This is the first evidence of nucleocytoplasmic Yorkie shift in association with the arrest of cell proliferation in a cnidarian, strongly evoking the cell division-promoting role of this protein and its inhibition by the activated Hippo pathway in bilaterian models. Our results furthermore highlight important differences in terms of deployment and regulation of Hippo pathway genes between cnidarians and ctenophores.
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie (UPMC), Institut de Biologie Paris-Seine (IBPS) CNRS, UMR 7138 Evolution Paris-Seine, Case 05, 7 quai St Bernard, 75005 Paris, France.
authors.forename: Alicia
authors.initials: A
authors.lastname: Coste
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie (UPMC), Institut de Biologie Paris-Seine (IBPS) CNRS, UMR 7138 Evolution Paris-Seine, Case 05, 7 quai St Bernard, 75005 Paris, France.
authors.forename: Muriel
authors.initials: M
authors.lastname: Jager
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie (UPMC), Institut de Biologie Paris-Seine (IBPS) CNRS, UMR 7138 Evolution Paris-Seine, Case 05, 7 quai St Bernard, 75005 Paris, France.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Chambon
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie (UPMC), Institut de Biologie Paris-Seine (IBPS) CNRS, UMR 7138 Evolution Paris-Seine, Case 05, 7 quai St Bernard, 75005 Paris, France.
authors.forename: Michaël
authors.initials: M
authors.lastname: Manuel
keywords: Cell proliferation; Cnidaria; Ctenophora; Development; Evolution; Growth; Hippo pathway; Yorkie