The first time the three children’s brains grew, things went so completely off the rails that they developed severe epilepsy and autism. Now biologists have used stem cells from these patients, who have a devastating disorder called Timothy syndrome, to grow their brains a second time — in miniature, in a lab dish.
The scientists reported in Nature on Wednesday that the mini-me cortices reprised the abnormal brain development so faithfully that the research might point the way toward preventing or treating the rare disorder.
Producing mini-Timothy-syndrome-brains-in-a-dish is only one of the remarkable new advances in the exploding science of “cerebral organoids,” miniature, three-dimensional human brain-like structures. These lab creations, scientists hope, will mimic severe psychiatric and neurological diseases such as schizophrenia, autism, and Alzheimer’s much better than mouse brains (the current go-to choice) do, revealing what goes wrong and offering a testing ground for experimental treatments.
But ever since cerebral organoids were first created from stem cells in 2013, they have ignited an intense ethical debate, including about whether they can suffer, feel pain, or be conscious — and whether they have human rights.
While that may seem far-fetched, a second study, also published in Nature Wednesday, described growing hundreds of cerebral organoids from the stem cells of healthy people for up to nine months and longer in special bioreactors. The mini-brains developed dozens of kinds of brain cells, from those that give rise to neurons in the cerebral cortex to those that connect the right brain and the left brain. And they linked up into working circuits — not producing thought or emotion, but pulsing with the same kind of electrical activity that enables human brains to do both.
“This shows that the approach has much greater potential than we ever imagined,” said Juergen Knoblich, of the Institute of Molecular Biotechnology in Austria, a pioneer in creating cerebral organoids who was not involved in either study. “They’ve shown that if you keep [the mini-brain] growing for a long enough time, it will generate the whole repertoire of cells we see in the human brain.”
Together, the new papers “give us unprecedented ways of looking at a human brain and its development,” said biologist Timothy O’Brien, of the University of Minnesota, who has also produced brain organoids from stem cells and was not involved in the new work. A key advance in both studies, he said, was “uncovering more layers of complexity, showing that these things really do look like human brains.”
In the Timothy syndrome study, scientists at Stanford University School of Medicine began with human cells called fibroblasts, donated by three patients. Using now-standard techniques, they put those cells through a biological time machine, returning them to an embryo-like stem cell state. By adding the proper nutrients, the researchers could not only spur these stem cells to grow into brain cells — done for more than a decade — but to form little balls.
Each is about 1/16 inch across and contains more than 1 million cells. Called cortical spheroids, they differ from cerebral organoids in that the former mimic specific regions of the brain, such as the front, rather than many sections.
Stanford’s Dr. Sergiu Pasca and his colleagues hoped the spheroids would reveal what goes wrong in Timothy syndrome. One batch mimicked a region deep in the brain, and another mimicked the cortex, the crevassed outer layer where thinking occurs. In fetuses, neurons from deep in the brain migrate and connect to neurons in the cortex, forming circuitry that supports thought, judgment, planning, and other higher-order functions.
After fusing the two cortical spheroids — cortex and deep layers — Pasca and his colleagues watched the neurons for days, seeing that those from the deep layer were terrible migrants. They stutter-stepped and stopped and started as if unsure whether or where to move. Yet they migrated more than neurons in normal brains, as if trying to make up for their confusion by barreling forward willy-nilly.
The spheroids, Pasca said, “help us see how brain development goes awry in patients with the different mutations linked to Timothy syndrome.” (Stanford has filed for a patent on generating brain-region-specific spheroids.)
Birey F, Andersen J, Makinson CD, Islam S, Wei W, Huber N, Fan HC, Metzler KRC, Panagiotakos G, Thom N, O'Rourke NA, Steinmetz LM, Bernstein JA, Hallmayer J, Huguenard JR, Paşca SP. Assembly of functionally integrated human forebrain spheroids. Nature. 2017 May 4;545(7652):54-59.
The development of the nervous system involves a coordinated succession of events including the migration of GABAergic (γ-aminobutyric-acid-releasing) neurons from ventral to dorsal forebrain and their integration into cortical circuits. However, these interregional interactions have not yet been modelled with human cells. Here we generate three-dimensional spheroids from human pluripotent stem cells that resemble either the dorsal or ventral forebrain and contain cortical glutamatergic or GABAergic neurons. These subdomain-specific forebrain spheroids can be assembled in vitro to recapitulate the saltatory migration of interneurons observed in the fetal forebrain. Using this system, we find that in Timothy syndrome-a neurodevelopmental disorder that is caused by mutations in the CaV1.2 calcium channel-interneurons display abnormal migratory saltations. We also show that after migration, interneurons functionally integrate with glutamatergic neurons to form a microphysiological system. We anticipate that this approach will be useful for studying neural development and disease, and for deriving spheroids that resemble other brain regions to assemble circuits in vitro.