Cnidarians have contributed greatly to our understanding of animal evolution, emergence of stem cell systems and innate immunity. Genomes of Nematostella, Hydra and Acropora digitifera have been sequenced with that of Acropora millepora and Clytia hemyspherica to appear in the near future.
At the same time surprisingly little is known at the molecular level about scyphozoan and cubozoan jellyfishes which represent the highest level of morphological sophistication among cnidarians. These animals possess advanced sensory organs, exhibit complex behavioural traits and in contrast to Nematostella, Hydra and Acropora have complex life cycles with alternation of polyp and medusa generations (see Fig.1).
Fig.1: Phylogenetic position of Scyphozoa and the metagenetic life cycle of Aurelia aurita with planula, polyp and jellyfish stages. Polyp-to-jellyfish transition is a remarkable example of metamorphosis.
Several interesting questions can be explored:
- • Is the life cycle regulation machinery of Medusozoa (Hydrozoa, Cubozoa and Scyphozoa) similar to that in Bilateria?
- • How does one genome regulate the development of three completely different life forms?
- • Which signalling cascades relay environmental cues into morphogenetic events?
In order to answer these questions we started to investigated the molecular machinery controlling polyp to jellyfish transition in a moon jelly Aurelia aurita (see Fig.2).
Fig.2: Strobilation in Aurelia aurita. Single polyp transforms into a stack of segments which further develop into young jellyfishes.
Our AURELIA PROJECT started with sequencing of polyp, strobila and ephyra transcriptomes (expression Atlas 454). Following the sequence assembly and data analysis, genes responsible for metamorphosis were identified by oligonucleotide microarrays (microarray Atlas).
During the project large amounts of data (protocols, sequences, images, etc.) were rapidly accumulating. In order to cope with all that data we developed a database with web interface which currently stores our results and can be used by the scientific community and general public.
In the moon jelly Aurelia aurita the molecular machinery controlling transition of a sessile polyp into a free swimming jellyfish includes both conserved pathways such as retinoic acid signalling, hedgehog, Wnt and TGFß as well as a family of novel Scyphozoa-specific genes. Our findings uncover for the first time the molecules controlling the metagenic life cycle in an ancient metazoan.