When scientists sequenced the Neanderthal genome in 2010, it became apparent that prehistoric dalliances had taken place between Neanderthals and our European and Asian ancestors.
A faint afterglow of these matings is still present in the genomes of modern humans. Around 2% of the genomes of non-Africans is of Neanderthal origin.
In some cases, carrying the Neanderthal version of a gene has been linked to changes in fat metabolism, depression and lupus risk.
But the mechanism behind such associations has remained a mystery.
In this study, researchers from the University of Washington looked at the RNA read-outs of Neanderthal gene variants in modern humans.
They used a database from the Genotype-Tissue Expression (GTEx) Project, and homed in on cases where a person had one human and one Neanderthal copy of any given gene.
Looking across 52 different body tissues, they compared the number of read-outs for the Neanderthal versus the human gene variant. This gave the researchers a picture of how ‘switched on’ Neanderthal genes are compared to their human equivalents, throughout the body.
The team looked at more than 2000 gene pairs. In 767 of these, either the Neanderthal or the human versions was consistently more ‘switched on’ across all tissues – the split was roughly 50-50.
Genes associated with auto-immune diseases, schizophrenia, cleft lip, depression, autism and obesity all cropped up as being regulated differently depending on their origin, and could explain why carrying Neanderthal versions of some genes changes disease risk.
In the brain and testes, read-outs of Neanderthal gene variants were especially low. This suggests that these tissues have undergone more rapid evolution since our divergence from the Neanderthal lineage some 700,000 years ago.
“Hybridisation wasn’t just something that happened 50,000 years ago that we don’t have to worry about anymore,” says geneticist Joshua Akey from the University of Washington, a co-author on the study. “Those little bits and pieces, our Neanderthal relics, are influencing gene expression in pervasive and important ways.”