Research | Functional palaeogenetics
Genetic basis of phenotypic differences
Melanie Pruvost | Holger Römpler | Nadin Rohland
- Blond mammoths
A new field of research that we recently started is the functional analysis of nuclear genes in both extant and extinct non-model organisms. As adaptation works through positive selection on nuclear genes we want to investigate candidate genes that are likely to contribute to adaptive differences between species. To show that such analyses are possible also for extinct species, we amplified and expressed one of the key genes for coat color, the MC1R gene from mammoth, in collaboration with Prof. Torsten Schöneberg and Dr. Holger Römpler from the University of Leipzig. This analysis showed that mammoths carried both a functional variant of this gene and one with strongly reduced activity. Intriguingly, a research team around Prof. Hopi Hoekstra from Harvard University identified the same mutation in a population of the mouse species Peromyscus polionotus where it is the major gene responsible for lighter hair color. Based on these results one can speculate that mammoths may have been polymorphic in coat color. Recently, together with Prof. Carles Lalueza-Fox from the University of Barcelona, we also investigated this gene in Neanderthals. We found a variant that does not occur in modern humans but also shows reduced activity. This result raises the possibility that some Neanderthals had lighter hair and skin color, similar to modern Europeans. We also amplified this gene in the extinct cave bear, but did not find any differences in the amino acid sequence compared to living brown bears. Currently we are investigating all living bear species, including coat color variants such as the golden moon bear, a blond variant of the Asian black bear, the glacier bear and several other variants.
- Red-haired Neanderthal
We also started to investigate the lysozyme gene in extant and extinct sloth species. It has been known for a long time that living tree sloths have a ruminant-like digestion. This type of digestion occurs also in true ruminants, colobine monkey and a bird, the hoatzin. Intriguingly, all these species have a specialized lysozyme that is expressed in the stomach and adapted to the low pH value there. Moreover, all species share certain amino acid substitutions that evolved in parallel due to the same evolutionary pressure. It has been shown only recently that living three-toed sloths also express a lysozyme in the stomach that works best at pH 3. However, to date no DNA sequences are available. We are currently developing an expression and test system for lysozyme and want to sequence the lysozyme gene from both the living tree sloth and at least one species of extinct ground sloth to better understand the digestive system especially of the extinct species.
Finally, in collaboration with Dr. Melanie Pruvost from the German Archeological Institute and Dr. Arne Ludwig from the Institute for Zoo and Wildlife Research in Berlin, we have started to investigate coat color variation in early domestic horses. Horses are exceptionally well suited for such studies as the genetic basis has been determined for the majority of coat color variants. Therefore, by typing a number of SNPs (single nucleotide polymorphisms) one can determine quite exactly what color a horse carried during life even from 10,000 year-old bones.
