Scientists unravel DNA of ancient horse

Scientists claim to have unravelled the DNA of an ancient ancestor of present day horse that lived some 700,000 years ago, a record-breaking feat in the young field of palaeo-genomics.

The find points to an ancient ancestor common to horses, donkeys and zebras who lived some four million years ago, twice as early as thought.

According to researchers, the breakthrough also raises hopes that many fossils deemed useless for DNA sampling might in fact be treasure troves of genetic information.

The team said in a report in the journal Nature, that the tale began 10 years ago, with the discovery of a piece of fossilised horse bone in the permafrost at a location called Thistle Creek, in Canada's Yukon territory.

According to French researcher Ludovic Orlando at the Centre for Geogenetics at Denmark's Museum of Natural History, it was a piece of metapodial bone from the leg.

He said it was a fragment about 15 centimetres long by eight centimetres wide.

It was revealed on radiodating the site where the bone was found, that the organic material there, decomposed leaves, etc, was deposited about 735,000 years ago.

Thanks to the deep chill, the sample had been astonishingly preserved but damage to its cells would have happened over the millennia limiting chances of teasing useful DNA out of it.

This find predates all previous ancient DNA sequences by over 500,000 years.

It was revealed in the initial analysis of the bone that despite previous periods of thawing during inter-glacial warm periods, the sample still contained biological materials - connective tissue and blood-clotting proteins - that were normally not present in the type of ancient material.

Pulverising a fragment of the bone, the multi-national team of researchers recovered its DNA. It was next subjected to high-throughput, gene sequencing to unravel the blueprint of ancient equine.

The first approach produced poor yields of horse-derived sequences, so they turned to a technology that could directly analyse single molecules of DNA.

This proved much more successful, however they still had an abundance of data to plough through.

With the help of high-powered computers and an existing horse genome sequence as a reference, the scientists identified the DNA motifs of the ancient horse , separating these from the DNA of contaminating organisms, such as bacteria accumulated from the environment.

From the resulting equine DNA fragments, they were able to reconstruct a draft of its genome and although the derived sequence data only covered around 70 per cent of the entire genome, this proved to be sufficient foundation for some revealing analyses.

(See: Genome of 700,000-year-old horse sequenced)