PASCA LAB Scientists know little about the earlier development of the human brain. As a result, they also have limited data about how exactly human brain development might relate to neuropsychiatric disorders, such as autism and schizophrenia. Since 2013, however , scientists having been learning the developing human brain using neurons derived from human caused pluripotent stem cells (iPSCs), which are cultured in 3 dimensions into pea-size structures that mimic the full body organ. Two studies published today (April 26) in Nature advance these research strategies. In one paper, Harvard’ s Paula Arlotta and co-workers described the development of organoids, or “ mini brains. ” In the other, Stanford’ s Sergiu Pasca and co-workers used neural spheroids— balls of tissue containing greater than a million neurons each— to study the interactions of 2 brain regions crucial to the development of the cerebral cortex.
“ The major conclusion is the confirmation/validation that the individual pluripotent stem cells are plastic enough to generate the particular diversity of cells necessary to recreate human, early stages associated with neurodevelopment in a dish, ” Alysson Muotri, who research neurological diseases using iPSCs at University of Ca, San Diego, but was not involved in either study, told The Scientist in an email. “ Every neuroscientist working with early brain development will be thrilled by reading these articles. ”
Scientists hope to use brain organoids and spheroids to study neurodevelopment and neuropsychiatric disorders; these mini brains have already been utilized to study Zika virus infection– linked microcephaly and autism spectrum disorders.
See “ Opinion: Brand new Models for ASDs”
Because many neuropsychiatric disorders are influenced by a person’ s genetics, it really is difficult to study these diseases in standard animal versions. Instead, these types of diseases “ must be modeled using the cellular material from the patient, because that’ s the only way that you can have the genome of that patient, ” Arlotta said. “ This really is really what justifies fundamentally the need for these human versions. ”
“ These two studies complement one another really well, ” University of Pennsylvania neuroscientist Guo-li Ming, who also was not involved in the work, wrote in an e-mail. “ The organoids generated are different in these 2 studies, with the Arlotta one using the whole-brain protocol plus focusing on cellular diversity. The Pasca paper, however, [involves] generating brain region-specific organoids plus try[ing] to put individual pieces together. ”
Pasca’ s team studied a phase in fetal brain development in which GABAergic, usually inhibitory interneurons in the deep forebrain migrate toward excitatory, glutamatergic neurons closer to the brain’ s dorsal surface— an area that develops into the cerebral cortex and contains both neuronal types. To that end, the researchers differentiated iPSCs to create both GABAergic and glutamatergic neural spheroids, fused the 2 spheroids in a tube, and observed their interactions.
As expected, the interneurons migrated, in a jumping, or even “ saltatory” manner, toward the glutamatergic neurons. Then, “ they change their morphology…. The dendrites they have become more complex, but more importantly they start making cable connections with the glutamatergic cells, ” Pasca told The Scientist . In spheroids derived from cells associated with patients with Timothy syndrome, a form of autism that comes from a gain-of-function mutation in a calcium channel, this immigration was aberrant; blocking the calcium channel with a medication restored normal migration.
“ Pasca’ ersus paper shows, for the first time, that assembling pieces of stem cell– derived human forebrain can be mimicked in vitro, ” Muotri wrote. “ This is important because several neurodevelopment problems have defects on these early stages, but [until now] there were no in vitro models to study these types of processes. ”
Arlotta’ s team modified a previous protocol for developing mini brains so they could survive for more than nine months— longer compared to had been achieved in previous studies. The brain organoids full grown to the point that they started to develop mature features, such as dendritic spines, and began firing in synchronized patterns feature of neuronal networks, the researchers reported. The group used single-cell mRNA sequencing to characterize the cellular types present in the brain organoids at both three months plus six months, finding that, by six months, the organoids included 7 different neuronal cell types, including retinal and cortical cells, and even more subtypes. Notably, the researchers found, the particular retinal cells responded to light.
“ Initially we have a system in which we use a normal, sort of semiphysiological sensory stimulus to stimulate neurons within the organoids, ” Arlotta said. This is important, she said, because in learning neuropsychiatric disorders, researchers want to study brain organoids within settings as close as possible to human physiological problems. “ Rather than generating optogenetic channels, here we have tissues that respond to normal sensory stimuli like light. ”
F. Birey et al., “ Assembly of functionally integrated human forebrain spheroids, ” Nature, doi: 10. 1038/nature22330, 2017.
G. Quadrato ou al., “ Cell diversity and network dynamics within photosensitive human brain organoids, ” Nature, doi: 10. 1038/nature22047, 2017.