Disruption of cortical excitatory and inhibitory neuron development has been implicated in autism spectrum disorder (ASD) by postmortem brain analyses and ASD risk genes. Identifying how key cortical lineages emerge and are balanced — in both neurotypical and ASD individuals — is therefore the critical next step.

In the current project, Flora Vaccarino and colleagues plan to use a multi-regional and topographically organized organoid system and a lentivirus barcoding system that tags the progeny of individual precursor cells to chart the emergence of excitatory and inhibitory lineages from common precursors. Their major goal is to decipher whether precursor cells from ASD individuals perform different lineage choices than neurotypical controls, explaining the altered balance between different types of neurons that are often observed. The transcriptome data that her lab will acquire in parallel with lineage tracing will allow further exploration of potential mechanisms underlying lineage imbalance in ASD.

Vaccarino’s team will simultaneously generate cortical, basal ganglia and thalamic organoids from induced pluripotent stem cells derived from both neurotypical and ASD individuals and characterize their cellular composition and spatial organization. They will also tag individual precursor cells within early basal ganglia, cortical and thalamic organoids, fuse the tagged organoids into cortico-basal ganglia-thalamic assembloids to promote neuronal network formation and maturation, and analyze the corresponding lineages to investigate the timing of lineage allocation, size of the progenitor pools and divergence from common progenitors.

Altered proportions of excitatory and inhibitory neurons have been postulated to occur in the forebrain of individuals with ASD, which in principle can be attributed to a variety of causes, from differential fate choice to differential proliferation, maturation and death. The impact of the proposed research will be to establish whether this neuronal imbalance is due to a true lineage imbalance (i.e., where certain progenitors are intrinsically programmed to make different fate choices) as opposed to an imbalance variably dictated by cell-extrinsic, microenvironmental cues.