View Full Version : Horsing around 800,000-years-ago: DNA of prehistoric stallion unveiled

06-26-2013, 09:41 PM
Horsing around 800,000-years-ago: DNA of prehistoric stallion unveiled after scientists extract proteins from fragment of foot bone
The DNA is 10 times older than any that has been previously recovered
Genome dramatically extends the known limit of DNA survival
Bone of the ancient animal found in frozen Canadian Yukon

The genome of a prehistoric horse that roamed the plains of Canada almost 800,000 years ago has been unveiled.
It is about 10 times older than any DNA ever recovered and comes from a fragment of the ancient animal’s foot that had been so remarkably preserved in permafrost scientists were able to extract blood proteins.
Dating up to 780,000 years ago, the bone sheds fresh light on equine evolution and dramatically extends the known limit of DNA survival.
Scientists extracted the DNA from two pieces of 700,000-year-old horse bone found in the frozen Yukon

Professor Ludovic Orlando, of Copenhagen University, and colleagues mapped the animal’s genes and compared them to another ancient horse from around 43,000 years ago as well as five contemporary breeds, the only surviving wild horse called a Przewalski and a donkey.

State of the art DNA analysis techniques allowed them to sequence 73 proteins, including some found in the blood.
The study, published in Nature, showed the Equus lineage that gave rise to all modern-day horses, donkeys and zebras originated around four million years ago - twice the conventionally accepted time.

The genome - or complete DNA - is almost 10 times older than the previous record which was for an early human called a Denisovan that lived about 80,000 years ago.

It shows horse populations have fluctuated multiple times over the past two million years particularly during times of severe climatic change.

There is also evidence for continuous change in horses’ immune system and sense of smell throughout evolution.
And the findings support evidence Przewalski’s horses represent the last living wild horse population and reveal genes that were probably selected during domestication.
The study suggests a significant fraction of DNA fragments could survive for over a million years in the geosphere.

The piece of bone was dug up a decade ago at a fossil site known as Thistle Creek in the Yukon Territory.
Researchers from Denmark, China, Canada, the U.S., Switzerland, UK, Norway, France, Sweden and Saudi Arabia all collaborated to sequence the genome.
DNA molecules can survive in fossils well after an organism dies.
They do not survive as whole chromosomes but as short pieces that could be assembled back together, like a puzzle, the University of Bristol.
The university said occasionally enough molecules survive so that the full genome sequence of an extinct species can be resurrected, such as was done with the horse.
Over the past few years, the full genome sequence of a few ancient humans, including the Neanderthal Denisovan genome, have been characterized.

In March, scientists completed the first complete Neanderthal genome sequence.
They used only a toe bone and a tiny fragment of finger to map out the entire genetic code of Denisovan man.

Evidence suggests that the Denisovans, a little-known ancient cousin of modern humans who lived in Siberia around 50,000 years ago, had dark skin, brown hair and brown eyes.

Prof Orlando said: 'We first got excited when we detected the signature of amino-acids that suggested proteins had survived.

'We got more excited when we proved able to directly sequence collagen peptides.
'When we detected blood proteins, it really started looking promising because those are barely preserved.
'At that stage, it could well be that ancient DNA could also be preserved.

'Our data represent the oldest full genome sequence determined so far.
'We also find that horse population size fluctuated multiple times over the past two million years, particularly during periods of severe climatic changes.

'We estimate the Przewalski’s and domestic horse populations diverged 38 to 72 thousand years before present and find no evidence of recent mixture between the domestic horse breeds and the Przewalski’s horse investigated.

'This supports the contention Przewalski’s horses represent the last surviving wild horse population.'
Named after a Russian explorer, Przewalski’s horses are native to Mongolia and once freely roamed the steppe along the China border.

They have since been kept and bred in captivity and have recently been reintroduced in Mongolia.
Dr Craig Millar, of the University of Auckland, and Prof David Lambert, of Griffith University in Australia, reviewed the study for the journal and said its implications go 'well beyond the evolution of horses.'

Dr Millar said: 'Until this study, many experts would have thought it was impossible to recover a genome from a sample of this age because of the rapid degradation of DNA into ever shorter fragments that occurs following the death of an organism.

'The decay is driven initially by the body’s own enzymes, and the actions of enzymes from microorganisms soon follow - death shuts down the normal defences that protect an organism against such fates.'