The human brain is dramatically expanded compared with other mammals such as rodents, and is three times larger than those of our closest relatives, the other great apes. How this human-specific expansion occurs is not yet known, mainly because of technical and ethical limitations with more traditional approaches. In order to investigate human brain expansion, we have performed comparative assays using cerebral organoids, a 3D self-organizing model of the developing brain. Our comparative analyses of human and great ape brain organoids reveal key differences in cell shape that uncover a previously unidentified transition phase of neural stem cells that is protracted in humans. These changes in cell shape affect tissue morphogenesis and thus influence size and neuron generation. Thus, our results suggest that by fine-tuning early cell shape transitions, evolution has found a way to influence brain size in dramatic ways.
Contact: martina.bernhard [at] mpi.nl