La conférence ayant été filmée, je joins ci-dessous la vidéo qui en a été tirée, également disponible directement sur le site du Collège de France.

Vous trouverez reproduit ci-dessous le résumé de la conférence que j’y ai animée avec Véronique Barriel le 12 juin 2009.

En 2004, à l’occasion de l’exposition ”Au Temps des Mammouths” présentée à la Grande Galerie de l’Evolution, paléontologues et biologistes moléculaires du Muséum national d’Histoire naturelle offraient en chœur une réponse négative à la question : ”Peut-on faire revivre le mammouth ?”. Pourtant, cinq ans plus tard, l’hebdomadaire New Scientist a présenté sous le titre ”Ten extinct beasts that could walk the Earth again”, les images de 10 animaux que la science pourrait bientôt ressusciter. Parmi les 10 bêtes listées, on trouve non seulement le mammouth laineux (Mammuthus primigenius), mais aussi l’homme de Néandertal (Homo neanderthalensis). Comment en est-on arrivé là ? Info ou intox ?
On peut toujours exclure le clonage ”au sens strict” d’espèces disparues : l’état avancé de dégradation post-mortem du matériel génétique et cellulaire semble irréversible. Néanmoins, les développements de la biologie moléculaire nous offrent aujourd’hui d’autres perspectives de résurrection fondées sur les progrès fulgurants dans le domaine du séquençage des génomes. Tandis que les premiers fragments d’ADN mitochondrial de mammouths laineux furent publiés dans Nature dès 1990, il a fallu attendre 1997 pour en connaître autant de notre plus proche cousin, l’homme de Néandertal, dont la région hypervariable HVR1 de l’ADN mitochondrial  du spécimen type de Feildhofer (1856) fut publiée dans la prestigieuse revue Cell. Si dans de nombreux laboratoires du monde entier on a vu dès lors fleurir des séquences d’ADN ancien de quelques dizaines de nucléotides, les progrès sont restés lents et le travail fastidieux : il a fallu attendre 2006 (pour le mammouth) et 2008 (pour Néandertal) avant de parvenir au séquençage complet de leur génome mitochondrial, ce petit génome circulaire d’origine bactérienne d’environ 16,000 nucléotides, cible privilégiée car présent en un nombre de copies cellulaires bien supérieur à celui de l’ADN nucléaire.
Avec ces séquences s’est imposé un constat flagrant : le séquençage de génomes nucléaires d’espèces éteintes par le couple classique PCR ciblée/clonage est vouée à l’échec, leurs 3 à 4 milliards nucléotides offrant un puzzle impossible à reconstruire ainsi. La révolution méthodologique est venue avec l’avènement de la méthode dite ”454″ de séquençage à la volée de banques d’ADN, parfaitement adaptée aux spécificités de l’ADN ancien, et qui permet de démultiplier les données génomiques tout en minimisant le coût, la main-d’œuvre et le temps nécessaires. Nous voilà à l’aube de l’achèvement de puzzles moléculaires de millions de pièces plus complexes que le séquençage du génome humain, et encore hors de portée il y a cinq ans.
En fait, dans le cas du mammouth comme de Néandertal, nous entrons déjà dans l’ère post-génomique des comparaisons fonctionnelles qui nous permettront, à terme, d’accéder à des informations biologiques qui ne se sont pas fossilisées : langage articulé, couleur des poils et des cheveux, adaptations métaboliques au froid glaciaire (etc) n’en sont que les prémices.
Quant à faire revivre ces organismes, c’est un pas qui a déjà été franchi pour des génomes viraux et bactériens ; nul doute que ce même pas sera franchi bientôt pour des génomes structurellement plus complexes comme celui du mammouth ou de Néandertal. Il est donc grand temps de nous interroger sur les implications éthiques de ces “progrès” dans la réalisation des rêves naguère chimériques de la biologie moderne.

“Le progrès c’est l’histoire des impossibilités réalisées”: le clonage du mammouth et de néandertal est-il en cours? de Régis & Véronique Barriel
In Programme et Résumés du Colloque “Cent cinquante après l’Origine des espèces: du darwinisme de Darwin à l’évolutionnisme contemporain”, page 35.

Genomics Digital Lab

Je viens d’achever un travail de traduction en version française du contenu de la suite éducative du “Genomics Digital Lab” (GDL), édité par la société canadienne Spongelab Interactive.

Cette suite de “jeux éducatifs multimédia” a déjà reçu de nombreux prix et reconnaissances (NSF, World Summit, Award, Apple Staff’s pick, Science magazine), et devrait être bientôt distribuée en France.

Le programme de la conférence>

This conference will provide an opportunity for secondary school science teachers to hear from some of Canada’s leading bioscience researchers and to learn about activities and programs that will help with their delivery in the classroom. Laboratory workshop sessions will permit participants to gain some experience in performing lab activities that complement the current educational curriculum. Information about academic and career choices for students will be highlighted. The program will address current research developments in bioethics, biodiversity, biopharmaceuticals, agri-foods, nanotechnology, and many other areas of investigation that fall under the rubric of bioscience. It will also offer information about academic and career opportunities for students.

Woolly mammoths’ last stand before extinction in Siberia wasn’t made by natives — rather, the beasts had American roots, researchers have discovered. Woolly mammoths once roamed the Earth for more than a half-million years, ranging from Europe to Asia to North America. These Ice Age giants vanished from mainland Siberia by 9,000 years ago, although mammoths survived on Wrangel Island in the Arctic Ocean until roughly 3,700 years ago. “Scientists have always thought that because mammoths roamed such a huge territory — from Western Europe to Central North America — that North American woolly mammoths were a sideshow of no particular significance to the evolution of the species,” said researcher Hendrik Poinar, an evolutionary geneticist at McMaster University in Hamilton, Canada.

To uncover the real history of woolly mammoths, Poinar and his colleagues spent the last three years extracting ancient DNA from 160 mammoth samples over much of their former range across Europe, Asia and North America, from which they assembled a family tree.

Many scientists had thought woolly mammoths were essentially one big family connected across the roughly 1,000-mile-long Bering Land Bridge that once joined Alaska to eastern Siberia.

Instead, the Bering Land Bridge might have been a significant barrier rather than an open corridor between the east and the west, as mixing between mammoths of the Old World and New World seems rare, the new research shows.

The bridge might have been tundra-like and not good at supporting these large creatures, the researchers explained. These divided groups of woolly mammoths then diverged genetically to become distinct populations.

Mysteriously, the Siberian mammoths then abruptly dwindled roughly 40,000 years ago, with American migrants replacing them rapidly, the study found.

“Something really happened to those Siberian guys,” Poinar said. “They literally fell off the face of the Earth and were supplanted by North American mammoths.”

These findings had eluded scientists in the past because such a genetic switch is “difficult if not impossible to tell by looking at teeth, tusks and bones,” Poinar explained.

While such population replacements are not uncommon on a small scale, “ones occurring on a continental scale certainly are,” said researcher Ross MacPhee, curator of mammalogy at the American Museum of Natural History in New York.

Mystery remains

As to what led to this continental-level decline, “there is a very large unknown looming here,” MacPhee said.

He does not think competition between the different mammoth populations is a likely culprit. Human over-hunting also does not make sense.

“You have humans in both Asia and North America at that time, but no drop-out in North America at that time,” he added. “Disease of course immediately comes to mind, but we have nothing to go on for that yet.”

Evolutionary geneticist Régis Debruyne at McMaster University in Hamilton, Ontario, noted that “for more than a century, any discussion on the woolly mammoth has primarily focused on the well-studied Eurasian mammoths. Little attention was dedicated to the North American samples, and it was generally assumed their contribution to the evolutionary history of the species was negligible. This study certainly proves otherwise.”

MacPhee said: “Right now it seems that mammoths had a very complicated demise. Enormous crashes seem to be part of their story — this enormous crash in Siberia might have been a prequel for their final loss.”

Analysis of the DNA reveals the Siberian mammoths that the North Americans replaced might not actually have been woolly mammoths, Mammuthus primigenius, but another, more archaic species.

On the other hand, the original Siberian mammoths might have been woollies that inherited DNA from other species through ancient hybrid ancestors, Poinar said.

Further genetic analysis could reveal which possibility is true, “and maybe help identify certain genes that gave an evolutionary advantage somehow that allowed one of the mammoth populations to survive and the other die off,” he added.

Debruyne, Poinar, MacPhee and their colleagues detailed their findings online Sept. 4 in the journal Current Biology.

Funding for this study was provided in part by Canada’s Natural Science and Engineering Research Council, the International Human Frontiers Science Program Organization, Canada’s Social Sciences and Humanities Research Council, the Canadian Research Chairs program and the Discovery Channel.

In a surprising reversal of conventional wisdom, a DNA-based study has revealed that the last of the woolly mammoths—which lived between 40,000 and 4,000 years ago—had roots that were exclusively North American. The research, which appears in the September issue of Current Biology, is expected to cause some controversy within the paleontological community.

“Scientists have always thought that because mammoths roamed such a huge territory—from Western Europe to Central North America—that North American woolly mammoths were a sideshow of no particular significance to the evolution of the species,” said Hendrik Poinar, associate professor in the departments of Anthropology, and Pathology & Molecular Medicine at McMaster University.

Poinar and Régis Debruyne, a postdoctoral research fellow in Poinar’s lab, spent the last three years collecting and sampling mammoths over much of their former range in Siberia and North America, extracting DNA and meticulously piecing together, comparing and overlapping hundreds of mammoth specimen using the second largest ancient DNA dataset available.

“Migrations over Beringia [the land bridge that once spanned the Bering Strait] were rare; it served as a filter to keep eastern and western groups or populations of woollies apart, says Poinar. “However, it now appears that mammoths established themselves in North America much earlier than presumed, then migrated back to Siberia, and eventually replaced all pre-existing haplotypes of mammoths.”

“Small-scale population replacements, as we call them, are not a rare phenomenon within species, but ones occurring on a continental scale certainly are,” says Ross MacPhee, curator of mammalogy at the American Museum of Natural History, and one of the researchers on the study. “We never expected that there might have been a complete overturn in woolly mammoths, but this is the sort of discoveries that are being made using ancient DNA. Bones and teeth are not always sensitive guides.”

“Like paleontologists, molecular biologists have long been operating under a geographic bias,” says Debruyne. “For more than a century, any discussion on the woolly mammoth has primarily focused on the well-studied Eurasian mammoths. Little attention was dedicated to the North American samples, and it was generally assumed their contribution to the evolutionary history of the species was negligible. This study certainly proves otherwise.”

The origin of mammoths is controversial in itself. Some scientists believe that the first proto-mammoths arose in Africa about seven-million years ago in concert with ancestors of the Asian elephant. Around five to six million years ago, an early mammoth species migrated north into China, Siberia and, eventually, North America. This early dispersal into North America gave rise to a new mammoth known as the Columbian mammoth. Much later, back in Siberia, a cold-adapted form—the woolly mammoth—evolved and eventually crossed over the Beringian land bridge into present-day Alaska and the Yukon.

What happened next, says Poinar, is a mystery: The Siberian genetic forms began to disappear and were replaced by North American migrants.

“The study of evolution is an evolution in itself,” says Poinar. “This latest research shows we’re drilling down and getting a closer and better understanding of the origins of life on our planet.”

Cette annonce a ete relayee par de nombreux medias, principalement sur le web:

E! Science News

It is common to think of the land bridge that existed from time to time across what is now the Bering Strait as a one-way affair. After all, the route through the area known as Beringia is thought to be how many animals and humans made their way out of Asia and into North America.

But there were no “Eastbound Only” signs. Some animals — camel ancestors, for example — went the other way, from North America into Asia. And there is no reason that a species could not go both ways, if conditions were right. That appears to be the case with the woolly mammoth, according to a major phylogenetic analysis.

Hendrik Poinar of McMaster University in Hamilton, Ontario, and colleagues looked at mitochondrial DNA from 160 mammoth samples from across Eurasia and North America as a way of determining who was related to whom. They identified several groups, or clades — some endemic to Siberia and other parts of Asia and others to North America, having been separated after mammoths first migrated eastward more than 1.5 million years ago.

But as they report in Current Biology, the researchers found that at some point in the last 150,000 years, North American mammoths migrated back to Siberia. “When they’re coming back in, the endemic Siberian populations start to crash,” Dr. Poinar said, and by about 40,000 years ago, the North American mammoths had completely taken over.

Whether the Siberian mammoths died out on their own (because of what is called genetic drift) or were outcompeted and outfoxed by their North American relatives is not known, though Dr. Poinar suspects it is not coincidental that the Siberian animals began to die out when North American animals started arriving.

Either way, the mammoths that finally became extinct about 10,000 years ago were not of Siberian lineage. “I’m not sure the Russians would be happy that their iconic wooly mammoth has North American origins,” Dr. Poinar said.

A lire sur le site de Scientific American, l’article de Jordan Lite, a propos de notre article sur la phylogeographie des mammouths pleistocenes.

What a long, strange evolutionary trip. The last of the woolly mammoths had North American, not Asian roots, new science suggests.
Many scientists thought the woolly mammoths — relatives of the elephant — represented one large population that spanned the Bering Land Bridge between present-day Alaska and Siberia.

Some of those mammoths crossed from Siberia into North America 200,000 years ago. Now, DNA analysis of woolly mammoth fossils shows that from 40,000 to 10,000 years ago, all of the beasts in Siberia showed North American genetic fingerprints, indicating that a cataclysmic event wiped out the species’ Siberian predecessors. The findings, based on analysis of 160 remains from North America, Europe and Asia, are in today’s Cell Biology.

“That we find such complete disappearance of the early Siberian groups is pretty remarkable,” said Ross MacPhee, curator of vertebrate zoology at the American Museum of Natural History, who co-authored the paper. “It sounds like something really bad happened around 40,000 years ago that resulted in their collapse on that continent. It’s a strange and provocative finding.”

Another author, Hendrik Poinar of McMaster University, said in a news release that the discovery suggests that woolly mammoths migrated across the Bering Land Bridge earlier than previously thought, then returned to Siberia to replace the older population.

Still unknown is how other species changed during the extinction of the Siberian woolly mammoth, MacPhee said.

“If we knew more about some of these other Ice Age species, we might know more about why these losses occurred in the first place,” he said. “It’s one of the biggest puzzles in extinction biology.”

Can the long-extinct mammoth be resurrected through the alchemy of modern biology?
Such hopes were raised yet again last week by the recent discovery, in the permafrost of Siberia’s Yamal peninsula, of a 6-month-old female that died perhaps 10,000 years ago.

“It’s a lovely little baby mammoth indeed, found in perfect condition,” Alexei Tikhonov, the deputy director of the Zoological Institute of the Russian Academy of Sciences, told Reuters last week.

The best hope would be if some of her eggs had been preserved in arrested state, much the way human eggs are stored in the freezers of fertility clinics. Sperm from an elephant could possibly tickle the egg awake from its long hibernation.

But mammoths rarely die in the controlled-temperature conditions necessary to preserve eggs without harm. Intact organs are seldom found. To retrieve viable sperm or eggs “seems an even more remote chance,” said Alex Greenwood, a biologist at Old Dominion University in Norfolk, Va., who has worked on mammoth DNA.

The alternative, far more laborious, would be to analyze the sequence of DNA units in the mammoth’s genome, make a copy of the DNA, and have it take over an elephant’s egg.

Each of those steps has long seemed impossible. But advances in the last few months have made each seem slightly less daunting. Analyzing the DNA sequence is complicated by the fact that ancient DNA, when it can be retrieved at all from fossil bones, is always highly degraded. The genome in every cell breaks down after death into thousands of small fragments of DNA.

But a new kind of DNA decoding machine happens to use such fragments as its starting material. At McMaster University in Canada, Hendrik Poinar and Régis Debruyne plan to use of one the machines, from 454 Life Sciences, to reconstruct a mammoth genome. The remaining obstacle is money. If they had $1 million, they could generate a rough draft of a mammoth genome in about a month, Dr. Debruyne said.

The reconstructed sequence of DNA units would then need to be turned into an actual mammoth genome. Mammalian genomes are made up of chromosomes of about 100 million DNA units in length and are beyond the capacity of current synthesis. Still, researchers at the Venter Institute in Rockville, Md., say they are close to synthesizing the genome of a bacterium that is 500,000 units long.

The third problem is that the DNA molecule in each chromosome is festooned with special proteins that control and read out its genetic information. No one knows how to add these proteins to DNA, but Venter Institute researchers showed last month that, at least in the case of bacteria, a naked piece of DNA inserted into a cell will somehow acquire the right control proteins and then take over the cell.

Resurrecting the mammoth is still not possible, but has become at least worth thinking about.