Highlights d A CRISPR interference platform for genetic screens in human iPSC-derived neurons d Survival screens uncover genes essential for neurons, but not iPSCs or cancer cells d Single-cell RNA-seq screens reveal distinct neuronal roles for ubiquitous genes d Arrayed high-content screens uncover genes controlling neuronal morphology

SUMMARY Parkinson’s disease is characterized by the progressive loss of midbrain dopamine neurons. Dopamine replacement therapy with levodopa alleviates parkinsonian motor symptoms but is complicated by the development of involuntary movements, termed levodopa-induced dyskinesia (LID). Aberrant activity in the striatum has been hypothesized to cause LID. Here, to establish a direct link between striatal activity and dyskinesia, we combine optogenetics and a method to manipulate dyskinesia-associated neurons, targeted recombination in active populations (TRAP). We find that TRAPed cells are a stable subset of sensorimotor striatal neurons, predominantly from the direct pathway, and that reactivation of TRAPed striatal neurons causes dyskinesia in the absence of levodopa. Inhibition of TRAPed cells, but not a nonspecific subset of direct pathway neurons, ameliorates LID. These results establish that a distinct subset of striatal neurons is causally involved in LID and indicate that successful therapeutic strategies for treating LID may require targeting functionally selective neuronal subtypes.

Supporting Information: Figure S1 Figure. S1 -Endogenous tagging of endolysosomal compartments (A) Representative fluorescence microscopy images of CRISPRi-HEK293T cells with RAB7A-mNG 11 endogenously labeled with the split-mNeonGreen system. Cells were treated with AF555-tau fibrils for 22 hours. (B) Representative fluorescence microscopy images of HEK293T cells with mNG 11 -RAB7A (top) or LAMP1-mNG 11 (bottom) endogenously labeled with the split-mNeonGreen system.