Rohit Bhattacharjee, Amity University, Kolkata
Analyses of endocasts revealing significant differences between Neanderthal and Homo sapiens neurocrania led to the conclusion that specific regions of the brain, especially the cerebellum, temporal and parietal lobes have expanded in the modern lineage owing to the differential growth of neural tissue. Other differences affecting subcortical regions are harder to detect but might exist. Although it is a challenge to probe the nature of brain tissue differences but the introduction to high-quality archaic genomes has opened many opportunities and research avenues to study the Homo sapiens brain evolution with unprecedented precision.
Researchers have explored the effects of Neanderthal and Denisovan introgressed variants in 44 modern human tissues finding downregulation by introgressed alleles in the brain, especially in the cerebellum and striatum. To determine the predicted expression of gene expression of the modern human-specific alleles, the advantage of the GTEX cis-eQTL dataset was taken enabling the researchers to think beyond variants affecting the structure and functionality of proteins and considering those that regulate genes expression. Data was extracted by determining Homo sapiens allele specificity using three high coverage archaic human genomes.
The variants list obtained shows regional enrichment of the modern human genome showing putative signals of positive selection bringing out the highly derived status of the cerebellum. Some of the genes affected by differential gene expression have been linked to clinical phenotypes or brain development, for example, BAZ1B, which is known to be responsible for craniofacial development in humans.
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