Content area
Full Text
The complexity of the human brain has made it difficult to study many brain disorders in model organisms, highlighting the need for an in vitro model of human brain development. Here we have developed a human pluripotent stem cell-derived three-dimensional organoid culture system, termed cerebral organoids, that develop various discrete, although interdependent, brain regions. These include a cerebral cortex containing progenitor populations that organize and produce mature cortical neuron subtypes. Furthermore, cerebral organoids are shown to recapitulate features of human cortical development, namely characteristic progenitor zone organization with abundant outer radial glial stem cells. Finally, we use RNA interference and patient-specific induced pluripotent stem cells to model microcephaly, a disorder that has been difficult to recapitulate in mice. We demonstrate premature neuronal differentiation in patient organoids, a defect that could help to explain the disease phenotype. Together, these data show that three-dimensional organoids can recapitulate development and disease even in this most complex human tissue.
Mammalian brain development beginswith the expansion of the neuroepitheliumto generate radial glial stemcells (RGs)1. These RGs divide at the apical surface within the ventricular zone (VZ) to generate neurons and intermediate progenitors. Intermediate progenitors populate the adjacent subventricular zone (SVZ), whereas neurons migrate through the intermediate zone to populate specific layerswithin the cortical plate. In humans, the organization of progenitor zones is markedly more elaborate; the SVZ is split by an inner fibre layer (IFL) into an inner SVZ and an outer SVZ (OSVZ)2. The OSVZ represents an entirely separate progenitor layer populated by intermediate progenitors and a unique stem cell subset termed outer radial glia (oRG)3,4, which are only present to a limited degree in rodents5. Both the IFL andOSVZ are completely absent in mice6. These key differences allow for the striking expansion in neuronal output and brain size seen in humans7,8.
Primary microcephaly is a neurodevelopmental disorder in which brain size is markedly reduced9. Autosomal-recessive mutations have been identified in several genes, all of which encode proteins localizing to the mitotic spindle apparatus10. Heretofore, primary microcephaly pathogenesis has primarily been examined inmousemodels.However, mouse mutants for several of the knowngenes11-14 have failed to recapitulate the severely reduced brain size seen in human patients.
Given the dramatic differences between mice and humans, methods that recapitulate paradigms of human brain...