The Developmental Brain Gene NPAS3 Contains the Largest Number of Accelerated Regulatory Sequences in the Human Genome

To identify the evolutionary genetic novelties that contributed to shape human-specific traits such as the use of a complex language, long term planning and exceptional learning abilities is one of the ultimate frontiers of modern biology. Evolutionary signatures of functional shifts could be detected by comparing non-coding regions that are highly conserved across mammals or primates and rapidly accumulated nucleotide substitutions only in the lineage leading to humans. Since gene loci densely populated with human accelerated elements (HAEs) are more likely to have contributed to human-specific novelties we sought to identify the transcriptional units and genomic 1 Mb intervals of the entire human genome carrying the highest number of HAEs. To this end we took advantage of four available datasets of human genomic accelerated regions obtained through different comparisons and algorithms and performed a meta-analysis of the combined data. We found that the brain developmental transcription factor NPAS3 contains the largest cluster of non-coding accelerated regions in the human genome with up to 14 elements that are highly conserved in mammals, including primates, but carry human-specific nucleotide substitutions. We then tested the ability of the 14 HAEs identified at the NPAS3 locus to act as transcriptional regulatory sequences in a reporter expression assay performed in transgenic zebrafish. We found that 11 out of the 14 HAEs present in NPAS3 act as transcriptional enhancers during development, particularly within the nervous system. Since NPAS3 is known to play a crucial role during mammalian brain development, our results indicate that the high density of HAEs present in the human NPAS3 locus could have modified the spatio-temporal expression pattern of NPAS3 in the developing human brain and, therefore, contributed to human brain evolution.