Thursday, July 12, 2012

Resurrection: bringing old genes back to life

As evolutionary processes such as selection pressure continue to endanger life's existence, many animal species have become extinct over the course of millions and billions of years. Once they go extinct, there is no way to bring them back on earth: a species is defined as a group of animals that are capable of interbreeding and producing fertile offspring. That means that once the last member of the group is gone, no new offspring of that species can be produced. A loss of animal species means a loss of biodiversity, which is why some scientists have tried to find ways to 'resurrect' extinct organisms, which also tells us something about why they went extinct. To do this, researchers try to obtain DNA still present on bones found from fossils or other remains. Because DNA contains the building blocks for building an organism, animal species can theoretically be brought back to life. Scientists from the Georgia Institute of Technology have set a first step in that direction.

A gene found in an ancient bacterium that roamed the earth 500 million years ago was of interest to the scientists. This gene, called Elongation Factor-Tu, still plays a role in survival of bacteria, but this particular ancient form is no longer around. Nevertheless, it can still be built into a bacterium and do its job, as the researchers proved. According to them, E. coli bacteria with the ancient gene have managed to survive for over a thousand generations, which means we can safely assume it is compatible.
While the gene does not give E. coli any particular ancient characteristics, this proof-of-principle does give scientists the possibility to study evolution. While that may not sound very interesting, it does tell us something about how life adapted over the course of hundreds of millions of years. "This is as close as we can get to rewinding and replaying the molecular tape of life", one of the scientists involved with the research said. Evolution pressurizes existence and forces change in genetic sequences in order to adapt to changing environments, which is why ancient genes help us reconstruct what happened in the past.

The scientists noted that bacteria supplied with the ancient EF-Tu gene were not as healthy as their modern-day counterparts. However, over time these particular E. coli strains recovered, and started growing at ordinary rates. That means the bacteria were able to adapt to the situation of having received an ancient survival gene, which  had not been exposed to the last 500 million years of evolution and gradual improvement. However, instead of the ancient EF-Tu mutating to a more modern form, the scientists found that the genes of proteins interacting with it were modified over time. It shows a novel evolutionary path lead up to the experimentally induced 'modernization' of E. coli.

By putting old genes in modern bacteria, the scientists hope to answer outstanding questions about evolution. But perhaps, we may also be able to bring back genes that control ancient features that we have not seen on the earth for millions of years. However, simply replacing a gene with an older counterpart is much easier than introducing genes in organisms that induce functional changes. Resurrection of ancient building blocks of life is nevertheless an interesting subject.
E. coli, as seen with an electron microscope.

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