TCD Scientists Discover Original Human Specific Genes

Posted on: 02 September 2009

Discovery of Novel Genes Could Unlock Mystery of What Makes Us Uniquely Human

Six million years since we shared a common ancestor with the chimpanzee,  researchers at Trinity College Dublin have made the first discovery of original human-specific genes.  The DNA of human and chimpanzee is 99% identical.  The small genetic differences between humans and chimpanzees have profound consequences and a major role in determining what it is to be human.  TCD scientists have now identified for the first time human-specific genes that originated during the evolution of humans following the separation from chimpanzees. These findings have just been published online in Genome Research. This research was supported by a President of Ireland Young Researcher Award from Science Foundation Ireland.

The prevailing wisdom in the field of molecular evolution was that new genes could only evolve from duplicated or rearranged versions of pre-existing genes.  It seemed highly unlikely that evolutionary processes could produce a functional protein-coding gene from what was once inactive DNA.

However, recent evidence suggests that this phenomenon does in fact occur.  Researchers have found genes that arose from non-coding DNA in flies, yeast, and primates.  No such genes had been found to be unique to humans until now, and the discovery by TCD scientists, Dr David Gonzalez Knowles and Dr Aoife McLysaght of the School of  Genetics and Microbiology and the Smurfit Institute of Genetics in Trinity College Dublin raises fascinating questions about how these genes might make us different from other primates.

Human evolution

In carrying out their research, the  TCD scientists conducted a rigorous evolutionary analysis of the human genome sequence in comparison with the genome sequence of other primates, including chimp and gorilla.  They searched for evidence of human genes that had newly-arisen since the common ancestor with chimpanzee and which are thus likely to have a role in human-specific traits.

They identified three human genes that have no counterpart in any other organism, not even the chimp, our closest relative.  “Then came the next challenge. We needed to demonstrate that the human DNA is really active as a gene,” commented  Dr McLysaght.

The researchers show that the human DNA is active as a gene because the proteins produced by these genes have been found.  These novel genes have originated from non-coding DNA during the 5-6 million years since we shared a common ancestor with chimp.  They estimate that around 18 human genes have originated by this mechanism during this time frame.

The authors gathered evidence from other studies that these three genes are actively transcribed and translated into proteins, but furthermore, they needed to show that the corresponding DNA sequences in other primates are inactive.  They found that these DNA sequences in several species of apes and monkeys contained differences that would likely disable a protein-coding gene, suggesting that these genes were inactive in the ancestral primate.

This discovery of novel protein-coding genes in humans is a significant finding, but raises a bigger question: What are the proteins encoded by these genes doing?  “They are unlike any other human genes and have the potential to have a profound impact,” Dr McLysaght noted. While these genes have not been characterised yet and their functions remain unknown, the TCD scientist added that it is tempting to speculate that human-specific genes are important for human-specific traits.