My postdoctoral research involved studying the evolution of gene regulation in primates. Since human and chimpanzee gene sequences are so similar, differences in the timing and position of gene expression are thought to be a major cause of the differences between the two species. The example I always give is that the genes responsible for hair growth are very similar in humans and chimps, but are expressed much more widely in our hirsute cousins.
The Brain Gain?
My own research focused on one gene at a time, but that’s an old school approach in a field that’s dominated by genome sequencing and high throughput analysis. Several recent studies have assessed global gene expression differences between humans and other primates, including a 2002 paper from Svante Pääbo’s group at the Max-Planck-Institute for Evolutionary Anthropology in Germany.
This paper caused quite a stir when I presented it at our lab’s monthly journal club. Pääbo’s group showed that the rate of change of gene and protein expression patterns was greatest in the human brain; in contrast, the patterns observed in the blood and liver were much more similar between species. It’s very gratifying and reassuring to us humans to confirm that it’s our brains that make us special.
You are what you eat
Now, 6 years later, the same group has published a new study that investigates a variable that is usually ignored; the effect of diet on gene expression. Lab mice were fed either their regular diet, the same diet as the chimpanzees in the Institute’s care (fruit, vegetables and, bizarrely, yoghurt), the cooked food from the Institute’s cafeteria, or McDonald’s fast food (the full list of foods given is available as Table S1 at the link above).
The gene expression patterns observed in the liver were significantly different between animals fed the mouse, chimp and human diets. However there was no significant difference between the gene expression patterns observed in the two human diet groups. This suggests that the inclusion of common features such as meat and other cooked foods, rather than the actual nutritional content of the diet, was the driving force behind the human-specific gene expression changes.
Interestingly, diet was thought to account for ~10% of human-chimp gene expression differences in the liver, but did not contribute to the different gene expression patterns observed in the brain.
This was a very thought-provoking study. New technologies allow us to do these amazing whole-genome comparisons, but we run the risk of letting our technical expertise get ahead of our ability to analyse the data, or proceeding too quickly to stop and think about hidden variables. It had never occurred to me that the results reported in the 2002 paper might be influenced by different diets. As it turns out, the rapid human-specific changes seen in the brain are probably still valid, but future studies are going to have to somehow incorporate and control for Pääbo’s new findings.
Interesting times ahead…
