Mapping cell-type- and age-dependent neuronal vulnerability through genome-wide in vivo CRISPRi screens in the mouse brain.

Current brain atlases are largely descriptive, cataloging correlative molecular snapshots such as gene expression signatures yet offering limited functional insight. Here, we develop a scalable, cell-type-resolved in vivo CRISPR interference (CRISPRi) platform enabling systematic gene function profiling in the mouse brain. Through genome-wide screens across four neuronal populations at three time points spanning youth to aging, we identify neuronal essential genes missed in vitro and define a consensus set of 269 neuronal core essential genes. The data reveal cell-type-specific genetic vulnerabilities, including divergent dependencies validated for exosome component 9 (Exosc9) and osteopetrosis-associated transmembrane protein 1 (Ostm1) between excitatory and inhibitory neurons. We uncover aging-specific dependencies enriched in mitochondrial and translational pathways, aligning with transcriptional changes in the aging human brain. Finally, we establish the CRISPRinvivo data portal as a community resource for in vivo screening. Altogether, this work provides a broadly applicable platform for in vivo functional genomics and a framework for building comprehensive gene-function brain atlases.