Jurassic Park. There, with that obvious reference out of the way, we can get started. Can we actually revive organisms (focusing on animals here) that have gone extinct? How? And how far away is it? These are the questions that form the backbone of a recent review article.
After a brief historical introduction, some new sources that can be and are used for aDNA recovery are discussed, each of which has contributed to the understanding of the life and evolution of extinct animals:
- Coprolites, or fossilized fecal material. Can contain DNA from both the animal and its food. (examples: moa, ground sloth.)
- Eggshells. Both from the in- and outside of ancient eggshells, DNA can be collected. (examples: Labrador duck, moas and other large, flightless birds, or ratites.)
- Feathers. Short sequences have been recovered from both the central shaft and the side-branches (or barbs) of feathers from extinct groups. (example: again moa.)
- Hair. Important source of aDNA. While the outside of the keratin shaft (fancy word for the hair) is prone to be contaminated by microbes, aDNA can be extracted from inside the hair, strongly decreasing contamination. (examples: wooly mammoth, bison, horse, human.)
- Sediment. It is even possible to extract aDNA from soil samples without any obvious, visible animal remains. (examples: large herbivores, such as horse and mammoths.)
These new materials that have proved suitable for ancient DNA extraction have contributes to our understanding of several animal groups. The authors mention the radiation of (yes, you guessed it) moa populations, the evolutionary relationships between bear groups (Polar, Cave and Brown), and, of course, the evolution and life of mammoths.
In fact, the wooly mammoth is the first extinct species to have its whole genome sequenced (in 2008). And more, ancient mammoth genes have even been activated. Both genes involved in hair color and hemoglobin expression have been activated. This latter effort, for example, has taught us that mammoth hemoglobin worked more efficiently in cold temperatures when compared to that of an Asian elephant.
Finally, the researchers discuss the possibilities with regard to resurrecting extinct species. They see three potential approaches:
- Nuclear transfer. According to the authors, at present the technique with the best chance of success. In short, nuclear transfer involves removing the nucleus from a donor cell and the insertion of the nucleus of the beastie we want. Recent research has shown this is possible with mice nuclei that had been frozen for 16 years. However, the writers caution, finding and inserting a nucleus of several thousands of years old is quite a bit harder. (But what about, for example, Tasmanian tigers, I wonder?)
- Chromosome reconstruction. Advances in DNA sequencing techniques, along with methods for successful extraction from old tissues, increase the possibility of obtaining fairly complete sequences from extinct animals. But, DNA needs to packaged in the right way, and with the correct extra materials, into chromosomes. This is hard for several reasons. Technologies for doing this are out there, but need further development in order to achieve this. If it can be made to work, however, it has the advantage that an intact nucleus of the extinct animal is not necessary.
- Gradual gene replacement. By gradually replacing genes in a living animal, perhaps reviving an extinct animal is possible? However, DON’T think about an elephant changing into a mammoth, or something like that. But, an animal’s development is largely controlled by genomic factors, one might wonder what can happen if, during development, an extant animal’s genes were gradually replaced by extinct counterpart (and the necessary control regions, transcription factors and other genetic stuff). This, as you can imagine, is the most contentious proposal and, if it works, expression of some extinct traits is more likely than the creation of a completely extinct animal.
Anyway, where does this leave us according to the authors? Well, here’s their conclusion:
The spectacular development of a fully functional ‘normal’ mouse from the nucleus of a cell from a mouse that had been stored at -20°C for 16 years, suggests that nuclear transfer technology might be the best candidate for the recovery of an extinct animal. In conjunction with recent chromosome reconstruction methods and gradual gene replacement methods, the recovery of an extinct animal may be entering the realm of ‘not quite so impossible’.
In other words, mammoths in the zoo won’t be for tomorrow, but might one day become a real possibility…
Huynen, L., Millar, C., & Lambert, D. (2012). Resurrecting ancient animal genomes: The extinct moa and more BioEssays DOI: 10.1002/bies.201200040