Introducing the brain: How human compares to primates (Introduction)

by David Turell , Friday, October 13, 2023, 16:57 (197 days ago) @ David Turell

Apes, Chimps, etc.:

https://www.sciencemagazinedigital.org/sciencemagazine/library/item/13_october_2023/414...

"RATIONALE: Single-nucleus RNA sequencing (snRNA-seq) offers a relatively unbiased characterization of cellular diversity of brain regions. Comparative transcriptomic analysis enables the identification of molecular and cellular features that are conserved and specialized but is often limited by the number of species analyzed. We applied deep transcriptomic profiling of the cerebral cortex of humans and four nonhuman primate (NHP) species to identify homologous cell types and human specializations.

***

"Profiling gorillas enabled discrimination of which human and chimpanzee expression differences are specialized in humans. We discovered that chimpanzee neurons have gene expression profiles that are more similar to those of gorilla neurons than to those of human neurons, despite chimpanzees and humans sharing a more-recent common ancestor. By contrast, glial expression changes were consistent with evolutionary distances and were more rapid than neuronal expression changes in all species. Thus, our data support a faster divergence of neuronal, but not glial, expression on the human lineage...We leveraged published datasets to link human-specific DEGs (differentially expressed genes) to regions of the genome with human-accelerated mutations or deletions (HARs and hCONDELs). This led to the surprising discovery that a large fraction of human-specific DEGs (15 to 40%), and particularly those associated with synaptic connections and signaling, were near these genomic regions that are under adaptive selection.

"CONCLUSION: Our study found that MTG (middle temporal gyrus) cell types are largely conserved across approximately 40 million years of primate evolution, and the composition and spatial positioning of cell types are shared among great apes. In each species, hundreds of genes exhibit cell type–specific expression changes, particularly in pathways related to neuronal and glial communication. Human-specific DEGs are enriched near likely adaptive genomic changes and are poised to contribute to human-specialized cortical function.re largely conserved across approximately 40 million years of primate evolution, and the composition and spatial positioning of cell types are shared among great apes. In each species, hundreds of genes exhibit cell type–specific expression changes, particularly in pathways related to neuronal and glial communication. Human-specific DEGs are enriched near likely adaptive genomic changes and are poised to contribute to human-specialized cortical function.

"Profiling gorillas enabled discrimination of which human and chimpanzee expression differences are specialized in humans. We discovered that chimpanzee neurons have gene expression profiles that are more similar to those of gorilla neurons than to those of human neurons, despite chimpanzees and humans sharing a more-recent common ancestor. By contrast, glial expression changes were consistent with evolutionary distances and were more rapid than neuronal expression changes in all species. Thus, our data support a faster divergence of neuronal, but not glial, expression on the human lineage. For all primate species, many differentially expressed genes (DEGs) were specific to one or a few cell types and were significantly enriched in molecular pathways related to synaptic connectivity and signaling. Hundreds of genes had human-specific differences in transcript isoform usage, and these genes were largely distinct from DEGs...This led to the surprising discovery that a large fraction of human-specific DEGs (15 to 40%), and particularly those associated with synaptic connections and signaling, were near these genomic regions that are under adaptive selection."

Comment: somehow, with very similar DNA's our brain cells are very different in type and organization. HAR's have been described here in the past as a driving reason for our evolutionary differences. None of the differences should be surprising. From a teleological viewpoint we are a very different result than one would expect based on what preceded us.