Sea urchins are echinoderms and belong to the deuterostome group. They occupy a phylogenetic position outside of the chordates, but are nevertheless closely related. They are bilaterians although adults have pentaradial symmetry (they belong to the same group as starfish). However, embryos have bilateral symmetry until metamorphosis. 

The species Paracentrotus lividus is found in the Mediterranean Sea, in the East Atlantic Ocean and even in the English Channel

EMBRC expertise:  

Access

• Optimised shipping conditions;
• Sex determination is carried out using electrical impulses;
• Optimisation of aquarium conditions and extension of the spawning period;
• Improvement of spawning conditions and life cycle can be managed to produce juveniles after 30 days of the larval phase (but 72 h between fertilisation and the last larval phase), fed with cultivated micro-algae;
• Induction of metamorphosis;
• Established protocol for holding coelomocytes (immune system cells) in culture conditions for 30 days.

Available tools

• This organism produces gametes in large quantities.  Fertilisation can be carried out in vitro with a fertilisation success of nearly 100%. Early development is synchronous, providing a large quantity of embryos at the same stage. This synchrony facilitates proteomics approaches, for example.
• The embryos are transparent and are thus suitable for cell imaging techniques, in toto hybridisation and immunohistochemistry and for the use of fluorescent markers.
• Functional analyses are straightforward; eggs and embryos of up to 8 cells can be micro-injected with synthetic RNA, anti-sense oligonucleotides and plasmids for the analysis of gene regulation. The embryos can be transplanted with cells. The genome can be modified using the TALEN technique.  
• Due to their small size, embryos are suited to pharmacological approaches, treatments with different types of molecule (chemical agents, natural substances) and require only small quantities.

Scientific advantages of this model organism   

• The sea urchin is an experimental model of choice for developmental biology.
• Their genome has not undergone total duplication, facilitating functional gene analyses due to the near absence of redundancy.
• The study of segregation of the endomesoderm lineage into the endoderm and the mesoderm, the emergence of left-right symmetry, the epithelial-mesenchymal transition, etc.
• Characterisation of the gene regulation networks (GRN) and signalling pathways that control these processes.
• It is another powerful model for studies on the cell cycle and translational control.
• Paracentrotus lividus has been chosen as a model in Europe for the large number of genomic tools that have been developed during the Marine Genomics programme.

Available genetic resources:

Given that its life cycle requires 2 to 3 years to reach sexual maturity, mutant lines are difficult to obtain.

Databases

• The genome of Paracentrotus lividus is currently being sequenced. Genomic tools are available for this species (cDNA and EST libraries, macroarrays)
• The genome of a closely related species found on the west coast of the United States Strongylocentrotus purpuratus was sequenced in 2006: 814 million base pairs and 23,000 genes.

Potential applications: 

• Eggs are simple and quick to use for bioassays, for screening for new anti-proliferative compounds, intracellular targets and toxins, for the assessment of the impact of heavy metals (Cu, Cr, Cd, Ni, etc.), pH, ions (PO4-2), contaminants, etc.  – system validated by the American Environmental Protection Agency (EPA).
• Toxicological risk assessment;
• Experimental model for designing an assessment method for testing the cancerogenic potential of molecules.