RNA exosome-mediated RNA surveillance governs developmental timing in the human cerebellum.

Defects in RNA metabolism are a defining feature of neurodevelopmental disease, yet how RNA decay pathways contribute to human brain development remains poorly understood. Mutations in ubiquitously expressed RNA surveillance factors often cause highly tissue-selective disease, highlighting a central paradox in human biology. The RNA exosome is a conserved ribonuclease complex traditionally viewed as a housekeeping machine for RNA turnover, yet recessive mutations in genes encoding structural subunits of the complex disproportionately cause neurological disease, suggesting an instructive role in nervous system development. Here, we show that the RNA exosome regulates the temporal progression of gene expression programs during human cerebellar differentiation. Using CRISPR-engineered human cerebellar organoids modeling EXOSC3 variants, we find that RNA exosome dysfunction does not broadly alter transcript abundance, but instead disrupts transitions between developmental states. Mutant organoids exhibit incomplete and mis-timed resolution of early transcriptional programs, altered lineage specificity, and impaired coordination of maturation-associated gene expression programs, with pronounced effects in neuronal lineages, particularly Purkinje cells and rhombic lip-derivatives. These defects are accompanied by disorganized laminar architecture and reduced coordination of neuronal activity, despite preserved intrinsic excitability. Together, our findings establish RNA surveillance as a key regulator of developmental timing, lineage fidelity, and neurodevelopmental disease.