How human brain development diverged from great apes

Since humans diverged from a common ancestor shared with chimpanzees and the other great apes, the human brain has changed dramatically. However, the genetic and developmental processes responsible for this divergence are not fully understood. Cerebral organoids (brain-like tissues), grown from stem cells in a dish, offer the possibility to study the evolution of early brain development in the laboratory.

Barbara Treutlein and Gray Camp, now at D-BSSE and IOB, and their colleagues analysed human stem cell-derived cerebral organoids for four months through their course of development from pluripotent stem cells, using single-cell RNA-seq and ATAC-seq data, to explore the dynamics of gene expression and regulatory landscape in human organoids. The authors then examined chimpanzee and macaque cerebral organoids to understand how organoid development differs in humans. “We observed more pronounced cortical neuron maturation in chimpanzee and macaque organoids compared to human organoids at the same point of development”, said co-lead author Barbara Treutlein. “This would suggest that human neuronal development takes place more slowly than in the other two primates.”

Independent from that, the researchers observed genes with human-specific differential expression during the process of neurogenesis and neuronal maturation compared to chimpanzee and macaque organoids, many of which can be further linked with human-specific changes in chromatin accessibility landscapes. The majority of these regulatory regions harbour changes in the DNA sequence that are shared among all humans living today.