An Irish geneticist has discovered that genes that work together to achieve a common result also tend to sit close to one another on the genome, writes Dick Ahlstrom
BIRDS OF A FEATHER flock together - and so, it seems do genes. Important research from Trinity College, Dublin, has shown that separate genes, whose proteins interact, often tend to be located close by one another within a person's genetic blueprint. The interacting genes form "clusters" and being near neighbours increases the chance that the cluster will be passed on to the next generation.
The work by Dr Aoife McLysaght and Takashi Makino appeared in the print edition of the prestigious journal, Molecular Biology and Evolutionrecently. The research focused on the idea that while genes within the DNA carry information, the actual structure of the genome also encodes biological information.
"The genome isn't just like a bag of genes or genes on a string," says McLysaght. She found that gene proximity on the genome has a biological function. "The genes beside one another are more likely to be connected."
McLysaght lectures in genetics in the Smurfit Institute of Genetics and in 2005 won one of the highest accolades given by research-funder Science Foundation Ireland - a SFI President of Ireland Young Researcher Award, presented by President McAleese.
The two researchers were looking for "gene clusters" in the human genome, closely linked genes whose resultant proteins were known to interact. Protein-to-protein interactions would usually occur where some important biological function was taking place, she says. "Gene clusters should exist. They have been known in bacteria for years, but this has been less clear in higher animals."
They started to search for gene clusters and immediately started to find them, discovering 83 pairs of interacting genes within a short length of DNA just a million steps long. Human DNA has about three-billion steps in total. "We were looking at these interacting genes and where they were located on a chromosome. They were more likely to be near one another."
This startling hit-rate was much higher than might have been expected as a chance occurrence, she says. And this in turn implies a powerful evolutionary advantage linked to clustered genes.
"If they are beside each other on the chromosome, they will be inherited together and transfer as a combination more often than if they were on separate chromosomes," McLysaght states.
"If there is a biological advantage to this, there should be evolutionary pressure to keep them together. That implies there is a biological meaning to having them close together."
Their search revealed much more. Many of the clusters involved genes that were an important part of the body's immune system, which protects against infection. "We looked at what the genes were and found they were often genes involved in the immune system. We didn't go looking for immune system genes, we were looking for clustered genes and they happened to be immune system genes."
They tended to be a part of the adaptive antibody-based immune response, something that in evolutionary terms emerged at about the time vertebrates started to appear in the fossil record. The adaptive system is well conserved in the vertebrate family but not in the invertebrates, which depend on a system known as the innate immune system.
This implies a powerful evolutionary link between gene clustering and the development of the adaptive immune response. "If this is really important, we should see it in all genomes," she says.
McLysaght's group is now looking at how the clusters evolved and if they evolved in a similar way across genomes. The initial results suggest gene clustering developed more strongly along the human lineage.