Evolution and humans: driven by transposons (Evolution)

by David Turell @, Tuesday, October 24, 2017, 20:14 (2364 days ago) @ David Turell

Studies of Neanderthal, Denisovan, and hominin genomes show that retrotransposons drove the development:



"Transposable Elements are biologically important components of eukaryote genomes. In particular, non-LTR retrotransposons (N-LTRrs) extensively shaped the human genome throughout evolution. In this study, we compared retrotransposon insertions differentially present in the genomes of Anatomically Modern Humans, Neanderthals, Denisovans and Chimpanzees, in order to assess the possible impact of retrotransposition in
the differentiation of the human lineage. Briefly, we first identified species-specific N-LTRrs and established their distribution in present day human populations. These analyses shortlisted a group of N-LTRr insertions that were found exclusively in Anatomically Modern Humans. Notably, these insertions targeted genes more frequently than randomly expected and are associated with an increase in the number of transcriptional/splicing variants of those genes they inserted in. The analysis of the functionality of genes targeted by human-specific N-LTRr insertions seems to reflect phenotypic changes that occurred during
human evolution. Furthermore, the expression of genes containing the most recent N-LTRr insertions is enriched in the brain, especially in undifferentiated neurons, and these genes associate in networks related to neuron maturation and migration. Additionally, we also identified candidate N-LTRr insertions that have likely produced new functional variants exclusive to modern humans, which show traces of positive selection and are now fixed in all present-day human populations. In sum, our results strongly suggest that N-LTRr
impacted our differentiation as a species and have been a constant source of genomic variability all throughout the evolution of the human lineage.


"The results presented in this study suggest that non-LTR retrotransposons mediated processes might have played a more than marginal role in recent human evolution. Their distribution in present-day individuals can be useful as a phylogenetic marker and highlights interactions and population dynamics that occurred after the separation from the chimpanzee lineage. RIs display patterns of maintenance and diffusion in modern populations that reflect slow but constant generation of variability. As the new variants can be co-opted at a later moment, selective pressures could arise resulting in the fixation of those variants. Indeed, non-LTR
retrotransposon activity results in an expansion of the genic pool of hominids, and can directly generate new functionalities for human genes and/or their transcripts. RIs are also possibly involved, as well, in the differentiation processes of the human brain and its increase in complexity that took place all throughout the evolution of the human lineage. In some instances, as for the AluYg6 insertion on chr1q25.3 and the AluYb9 insertion on chr10q25.3, the effects of RIs on their target in cis might have been key contributors to the molecular differentiation of the AMH genomes. Indeed, the impact of non-LTR retrotransposonsons on human evolution described here likely reflect the tip of a much large iceberg, as our study is limited to a few Neanderthal, Denisovan and Chimpanzee genomes, and because only RI-impacts on cis could be analyzed. However, the contribution of non-LTR retrotransposition, whose understanding still needs to be further developed, is starting to shed light on the variety and complexity of RI-driven evolutionary processes that
shaped our genome and will continue to influence our evolution in the future. "

Comment: We can see that evolution at this stage of human development appears driven by retrotransposons hopping around the genome. The case can be made hat it was God driven, since the improvements happened over such a short time of 8 million years. Chance random mutations would not do this, according to theory. Specific segments of a certain order of bases is required.

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