Unique immune system in Atlantic cod
An international team of researchers has used high-throughput sequencing technology to make a striking discovery that changes fundamental ideas about the evolution of the immune system in vertebrates. These results are published in Nature.
The team, led by researchers from the University of Oslo, and including collaboration from the Wellcome Trust Sanger Institute, found that an important component of the immune system is absent in Atlantic cod. In other vertebrates, including humans, this component helps fight disease due to bacterial infections and parasites.
“The overall aim of this initiative was to obtain the entire genome sequence of the Atlantic cod by utilizing new technology. We had not expected to find that Atlantic cod has lost such a crucial component of its immune system.
“All vertebrates, including humans, have a complex immune system that fights disease. This immune system, like the genetic code, originated only once in evolutionary history. Therefore, all vertebrates share similar components of this system and we expected that Atlantic cod possessed a minimum set of genes responsible for these components. Nevertheless, despite some very hard searching, we concluded that some genes were missing.”
Professor Kjetill S. Jakobsen at the Centre for Ecological and Evolutionary Synthesis (CEES) University of Oslo, who led the team of researchers
In fact, Atlantic cod has lost the genes that are essential for the function of the major histocompatibility complex (MHC) II pathway. In humans, the malfunction of this pathway leads to severe disease or even death. Atlantic cod, however, is not exceptionally susceptible to disease under natural conditions.
Interestingly, other genes in the Atlantic cod genome are far more numerous than expected. For example, a highly expanded number of MHC I genes and Toll-like receptor (TLR) genes were found, indicating that Atlantic cod relies relatively more on these genes for its immune response and has developed unique mechanisms to deal with bacterial infections.
Knowledge of such alternative mechanisms will greatly help understanding of the evolution of immune function in vertebrates and even humans, and will allow for more targeted vaccine development – aiding disease management and the process of domestication of Atlantic cod.
“Ensembl provided the gene annotation for cod. This assembly was one of the first based on new sequencing technology reads that we’ve annotated. We applied a combination of methods previously used in other genomes, aligning protein evidence from other species, and projecting annotation from another fish species. The projection method combines parts of the assembly together where necessary to create more complete gene models.”
Dr Steve Searle Joint Head of Vertebrate Genome Annotation, from the Sanger Institute
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The Wellcome Trust Sanger Institute
The Wellcome Trust Sanger Institute, which receives the majority of its funding from the Wellcome Trust, was founded in 1992. The Institute is responsible for the completion of the sequence of approximately one-third of the human genome as well as genomes of model organisms and more than 90 pathogen genomes. In October 2006, new funding was awarded by the Wellcome Trust to exploit the wealth of genome data now available to answer important questions about health and disease.
The Wellcome Trust
The Wellcome Trust is a global charitable foundation dedicated to achieving extraordinary improvements in human and animal health. We support the brightest minds in biomedical research and the medical humanities. Our breadth of support includes public engagement, education and the application of research to improve health. We are independent of both political and commercial interests.
