Stem Cell-Based Cerebral Organoids Enable in Vitro Study of Human Brain Development and Microcephaly

Investigators at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences (Vienna) have developed a human pluripotent stem cell-derived three-dimensional organoid culture system, termed cerebral organoids, which develop various discrete, although interdependent, brain regions. These include a cerebral cortex containing progenitor populations that organize and produce mature cortical neuron subtypes.

The investigators reported in the August 28, 2013, online edition of the journal Nature that after 15–20 days of culture growth cerebral organoids formed that consisted of continuous tissue (neuroepithelia) surrounding a fluid-filled cavity that was reminiscent of a cerebral ventricle. After 20–30 days, defined brain regions, including a cerebral cortex, retina, meninges, as well as choroid plexus, developed. After two months, the mini-brains reached a maximum size, but they could survive indefinitely (currently up to 10 months) in a spinning bioreactor. Further growth, however, was not achieved, most likely due to the lack of a circulation system and hence a lack of nutrients and oxygen at the core of the mini-brains

Cerebral organoids were shown to recapitulate features of human cortical development, namely characteristic progenitor zone organization with abundant outer radial glial stem cells. The investigators used RNA interference and patient-specific induced pluripotent stem cells to model microcephaly, a disorder that has been difficult to recapitulate in mice. They demonstrated premature neuronal differentiation in patient organoids, a defect that could help to explain the disease phenotype.

Senior author Dr. Jürgen Knoblich, deputy scientific director of the Institute of Molecular Biotechnology of the Austrian Academy of Sciences, said, "We modified an established approach to generate so-called neuroectoderm, a cell layer from which the nervous system derives. Fragments of this tissue were then maintained in a 3D-culture and embedded in droplets of a specific gel that provided a scaffold for complex tissue growth. In order to enhance nutrient absorption, we later transferred the gel droplets to a spinning bioreactor. Within three to four weeks defined brain regions were formed."

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