DNA from the ancient hominins, Neanderthals and Denisovans, was inherited by modern humans. These archaic variants are mostly neutral, but some have been found to result from positive selection. In other words, these variants may have improved survival by helping humans adapt to new environments as they populated the world.
In this study, researchers examined the MUC19 gene, which encodes a mucin related to immunity, in admixed Americans. They found a haplotype that originated in hominins. This DNA includes features linked to Denisovans, but it was first passed through Neanderthals before reaching modern humans. This genetic region is also surrounded by an extended copy of a tandem repeat. Based on positive selection patterns, we can indicate this haplotype was favored by natural selection in Indigenous American populations while their ancestors were migrating into the Americas.
It was found that modern admixed Americans had an increased number of variable number tandem repeats at the MUC19 gene. The tandem repeat expansion increased the length of an exon coding for a MUC19 protein. We can also see that there is a relationship between the number of VNTRs and the number of introgressed haplotypes, in which individuals with introgressed haplotypes had a higher number of VNTRs. Furthermore, it was found that there are high frequencies of nine Denisovan variants of the archaic haplotype in American populations.
Overall, this study highlights the importance of the MUC19 gene for studying adaptive introgression. Through this, multiple introgression events can be observed: Denisovans to Neanderthals and Neanderthals to modern humans. This research has the future potential to help explain how indigenous Americans adapted to their environments.
Article link:
https://www.science.org/doi/10.1126/science.adl0882
Additional source:
https://newsroom.uw.edu/news-releases/archaic-gene-variant-may-have-aided-adaptation-to-americas/
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