A man by the genome of Atapuerca - The País.com (Spain)

hominid fossils at the Sima de los Huesos at Atapuerca (Burgos), 400,000 years ago, forming the world’s largest collection of Middle Pleistocene human remains. And, so far, the oldest DNA recovered in temperate zones, ie not frozen in high latitudes, is around 100,000 or 120,000 years. It is a large distance. But scientists have overcome a major jump with a technical advance that can have huge implications on human paleontology. An international team, including Spanish researchers has succeeded in sequencing the mitochondrial genome from smaller DNA fragments obtained in samples from a bear bone which are mixed with fossils of hominids.

With this new technique, the genome of those preneandertales seems to be getting closer. “We hope that the methodology presented here will help to recover ancient DNA sequences from other organisms of the Middle Pleistocene. Fossils from the Pit of Bones are the target of such efforts, “write Jesse Dabney and his colleagues in the journal Proceedings of the National Academy of Sciences (USA) in presenting this week the complete mitochondrial genome of those ancestors of cave bears.

DNA is recovered oldest unfrozen areas

“Yes, of course I am optimistic about the possibility of obtaining DNA from human fossil pit, if any in the bear bones can have on contemporary human bones of those, what we have now with Bear DNA was not feasible very recently, “said Juan Luis Arsuaga, co-director of Atapuerca site and one of the authors of the new research. “And the human DNA of the chasm, mitochondrial also allow us to know his exact relationship to Neanderthals, modern humans and the common ancestor.”

Arctic ice cores were recovered and DNA fragments of plants and invertebrates around 800,000 years ago and was introduced last June a draft genome of horse bones from 560,000 to 780,000 years were preserved in permafrost in northern Canada. But in more temperate climates, the DNA does not keep well and so far, not been able to exceed the 100,000 or 120,000 years. The problem is that DNA degrades fragmented.

“Only trace amounts of DNA occasionally survive the decomposition of organic matter for a long time after the death of an organism,” the researchers explain. However, “the recovery of these ancient DNA molecules is very difficult because of their small size,” he added in his article.

Now these scientists, led by Jesse Dabney, Department of Evolutionary Anthropology Max Planck Institute (Germany) and with the participation of leading world authority on ancient DNA Svante Pääbo, have developed the methodology that allows them to work with fragments DNA tiny (only 30 bases, the chemical letters of genes) and reconstruct the genome of the mitochondria (cell organelle) that has about 16,000 bases. Also, they get enough copies to get high reliability. In this, he points Arsuaga, bioinformatics is essential.

These results “demonstrate that DNA can survive hundreds of thousands of years out of the permafrost and opens the prospect of getting more samples from this period are accessible to genetic studies,” the researchers write in Proceedings . Arsuaga sure that other teams are going to try now with other fossils.

As for the DNA

the cell nucleus, which give key information about the characters of individuals, of fossils as old … “I do not know, today nobody has succeeded” answers Arsuaga wisely. It also warns that the move to work with ancient DNA of bears and humans is not as easy as it might seem because, in the case of humans, scientists are faced with the problem of contamination of the samples, which requires a strict protocols of laboratory manipulation, while DNA bear current is not exactly in the environment.

The discovery of these molecules is difficult because of their small size

bear remains (Ursus deningeri ) in Atapuerca are very abundant in the Pit of Bones, which houses more than 200 fragments of skeletons. Some of them are on the same level of the reservoir that the remains of at least 28 human rescued so far. They had a size similar to modern brown bear and were ancestors of cave bears, huge animals that became extinct some 28,000 years ago. The mitochondrial genome analysis shows that ursus deningeri is an early divergence of the lineage to which they belong all cave bears of western Europe in the late Pleistocene, Dabney and colleagues conclude.

“Mitochondrial DNA is optimal to take the evolutionary tree species,” says Arsuaga, Professor of Paleontology at the University Complutense of Madrid and director of the Center for Research on Evolution and Human Behavior (from the Complutense and the Institute de Salud Carlos III). The same center are investigating two other authors of the article Proceedings : Cristina Valdiosera and Nuria Garcia bear expert.