Rapid generation of ventral A9-like dopaminergic neurons from patterned iPSCs.

In vitro modelling of highly vulnerable nigral dopaminergic (DA) neuronal subtypes in Parkinson's disease (PD), is necessary for studying disease mechanisms. Here, we optimized a new approach by expressing the pioneer neurogenic transcription factor, Achaete-scute-like 1 (Ascl1), implicated in determining dopaminergic fate. Sequential small-molecule patterning of iPSCs into early floor plate mesencephalic progenitors, followed by inducible Ascl1 expression, rapidly differentiates midbrain DA neurons. Immunocytochemistry and transcriptomic analysis of these patterned Ascl1-driven DA neurons (PA-DANs) confirmed midbrain-lineage specificity. Importantly, we found an enrichment of DA subpopulations that corresponded to the adult human ventral SOX6-positive A9 DA subtypes vulnerable in PD. Furthermore, we combined these ventral A9-like PA-DANs with human iPSC-derived midbrain astrocytes and microglia in defined ratios to generate mature 3D A9-like assembled organoids that display characteristic spontaneous neuronal activity and electrical propagation along the axon. Our method efficiently generates a mature and functional A9-like DA neuronal platform to study PD.