The Clytia genome reveals the origins of the jellyfish

Méduse Clytia © Marion Lechable and Alexandre Jan
Méduse Clytia © Marion Lechable and Alexandre Jan

Research teams from the Villefranche-sur-Mer Developmental Biology Laboratory (jointly managed by Sorbonne University and CNRS), in collaboration with the Biological Institute Paris-Seine (Sorbonne University), CEA-Genoscope and the University of Vienna have decoded the genome of the jellyfish Clytia. Their study some of which are also present in humans, and questions the evolutionary origin of this cnidarian that appeared more than 500 million years.

Most people associate jellyfish with rather unpleasant and painful encounters at the beach. The Australian "sea wasp" box jellyfish is among the most toxic animals on the planet. Jellyfish, as well as corals, sea anemones and the freshwater polyp hydra belong to the cnidarians, a very old lineage of stinging animals. Jellyfish, however, are not all dangerous: most of those of the hydrozoan group are less than a few centimeters and harmless to man. They include the common species Clytia hemisphaerica, whose genome has been decoded by researchers from the Developmental Biology Laboratory of Villefranche-sur-Mer in collaboration with the Genoscope, a team of the IBPS (Sorbonne University) and the University of Vienna.
This jellyfish is currently being adopted as a new lab-rat for experimentation by several laboratories around the world. Behind the simplicity of this species (and of many other species of jellyfish) lies a complex life cycle alternating between three forms. A swimming larva metamorphoses into a polyp living on the bottom of the sea, which generates by budding the swimming jellyfish.
This first analysis of the Clytia genome focused on uncovering which genes are involved in making the jellyfish form. The researchers surprisingly discovered that only a small proportion of "new" genes special to the jellyfish were involved. These animals were thus mainly constructed during evolution by reusing ancient genes. Some of the many ancient genes in the Clytia genome were previously well known for regulating embryonic development in other animals, including humans. But in Clytia, these "old" genes have a new function: Instead of regulating development of the embryo, they act in the nervous system and tentacles of the adult jellyfish.

Analysis of the Clytia genome has thus revealed that the jellyfish uses some ancient genes along with a few new ones in novel combinations. These fascinating creatures certainly will have many other surprises to reveal.


The genome of the jellyfish Clytia hemisphaerica and the evolution of the cnidarian life-cycle , L. Leclère, C. Horin, S. Chevalier, P. Lapébie, P. Dru, S. Peron, M. Jager, T. Condamine, K. Pottin, S. Romano, J. Steger, C. Sinigaglia, C. Barreau, G. Quiroga Artigas, A. Ruggiero, C. Fourrage, J. E. M. Kraus, J. Poulain, J-M. Aury, P. Wincker, E. Quéinnec, U. Technau, M. Manuel, T. Momose, E. Houliston and R. R. Copley. Nature Ecology & Evolution.

[1] These results corroborate the conclusions of a recently published study: The genome of the jellyfish Aurelia and the evolution of animal complexity, David A. Gold et al., Nature Ecology & Evolution 3, 96-104.