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Nat Ecol Evol. 2019 May;3(5):801-810. doi: 10.1038/s41559-019-0833-2. Epub 2019 Mar 11.

The genome of the jellyfish Clytia hemisphaerica and the evolution of the cnidarian life-cycle.

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Laboratoire de Biologie du Développement de Villefranche-sur-mer, Sorbonne Université, CNRS, Villefranche-sur-mer, France.
Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Marseille, France.
Evolution Paris-Seine, Institut de Biologie Paris-Seine, Sorbonne Université, CNRS, Paris, France.
Institut de Systématique, Evolution, Biodiversité (ISYEB UMR 7205), Sorbonne Université, MNHN, CNRS, EPHE, Paris, France.
Laboratoire de Biologie du Développement (IBPS-LBD, UMR7622), Sorbonne Université, CNRS, Institut de Biologie Paris Seine, Paris, France.
Institut de Génomique Fonctionnelle de Lyon, École Normale Supérieure de Lyon, CNRS UMR 5242-INRA USC 1370, Lyon cedex 07, France.
The Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL, USA.
Centre de Recherche de Biologie cellulaire de Montpellier, CNRS UMR 5237, Université de Montpellier, Montpellier Cedex 5, France.
Service de Génétique UMR 781, Hôpital Necker-APHP, Paris, France.
Department for Molecular Evolution and Development, Centre of Organismal Systems Biology, University of Vienna, Vienna, Austria.
Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway.
Génomique Métabolique, Genoscope, Institut François Jacob, CEA, CNRS, Univ Evry, Université Paris-Saclay, Evry, France.
Genoscope, Institut de Biologie François-Jacob, Commissariat à l'Energie Atomique, Université Paris-Saclay, Evry, France.
Laboratoire de Biologie du Développement de Villefranche-sur-mer, Sorbonne Université, CNRS, Villefranche-sur-mer, France.


Jellyfish (medusae) are a distinctive life-cycle stage of medusozoan cnidarians. They are major marine predators, with integrated neurosensory, muscular and organ systems. The genetic foundations of this complex form are largely unknown. We report the draft genome of the hydrozoan jellyfish Clytia hemisphaerica and use multiple transcriptomes to determine gene use across life-cycle stages. Medusa, planula larva and polyp are each characterized by distinct transcriptome signatures reflecting abrupt life-cycle transitions and all deploy a mixture of phylogenetically old and new genes. Medusa-specific transcription factors, including many with bilaterian orthologues, associate with diverse neurosensory structures. Compared to Clytia, the polyp-only hydrozoan Hydra has lost many of the medusa-expressed transcription factors, despite similar overall rates of gene content evolution and sequence evolution. Absence of expression and gene loss among Clytia orthologues of genes patterning the anthozoan aboral pole, secondary axis and endomesoderm support simplification of planulae and polyps in Hydrozoa, including loss of bilateral symmetry. Consequently, although the polyp and planula are generally considered the ancestral cnidarian forms, in Clytia the medusa maximally deploys the ancestral cnidarian-bilaterian transcription factor gene complement.

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