A paper, published on March 6th in the open access journal Public Library of Science (PLoS) Genetics, shows an unexpected discovery: a gene which had long been silenced, became functional again in the course of the evolution of the great apes, humans among them, some twenty million years ago.

Nowadays, this gene- known as IRMG- plays a role in the human immunological system and is of great medical interest due to its potential involvement in an important digestive inflammatory disorder: Crohn's disease.

This Research was performed by Cemalettin Bekpen and directed by Evan Eichler (University of Washington, Seattle, USA) together with a team of researchers, among whom is Tomàs Marquès-Bonet, co-author of the work and researcher at the Evolutionary Biology Institute (UPF-CSIC), now doing postdoctoral research at Washington University.

Tomàs Marquès-Bonet highlights that "in this research we prove, for the first time, the death of the gene in the common ancestor of the apes of the New and the Old world and its later resurrection in the lineage of great apes and humans. As this gene is linked to our system to combat pathogens, we can speculate as to the possible repercussions that this gene has had in expansion into new territories or its connection with certain diseases. Again, genetics provides us with an excellent example of plasticity and adaptation to the environment"

Repeated and mobile DNA fragments are able to generate changes in the genome

By reconstructing the evolution of the gene throughout its history, this research has proved that approximately 20 years ago, a mobile element of the genome's DNA located itself before the silenced gene and, by regenerating its promoter area, awakened it. Some mammals, such as rodents, still have several copies of the IRMG gene, but as primates evolved, they had gradually lost it until having a single, inactive copy of this gene, some 50 million years ago.

This discovering constitutes new evidence that the genome, far from being something static, is dynamic and flexible and continuously changing. This flexibility can be especially useful in the battle against resistant infectious agents.

"The human genome contains hundreds of genes which have been silenced at some point and we now know that could become functional again and even change the evolutionary course of our species. We cannot  say that a gene is dead until it is definitively eliminated from the genome" said Tomàs Marquès-Bonet.

The above graphic sums up the death and resurrection of the IRGM gene in humans. According to the commonly accepted phylogenetic tree for primates, green indicates the functional gene and red the silenced gene. Genetic analysis suggests that this gene disappeared around 50 million years ago as a result of genetic changes that interrupted its expression and functionality.

Reference Works:

Cemalettin Bekpen, Tomas Marques-Bonet, Can Alkan, Francesca Antonacci, Maria Bruna Leogrande, Mario Ventura, Jeffrey M. Kidd, Priscillia Siswara, Jonathan C. Howard, Evan E. Eichler (2009), "Death and Resurrection of the Human IRGM Gene, PLoS Genetics. doi:10.1371/journal.pgen.1000403.