Injury-induced ASCL1 expression orchestrates a transitory cell state required for repair of the neonatal cerebellum.

To understand repair processes, it is critical to identify the molecular foundations underlying progenitor diversity and plasticity. Upon injury to the neonatal cerebellum, a normally gliogenic -expressing progenitor (NEP) in the Bergmann glia layer (BgL) undergoes adaptive reprograming to restore granule cell production. However, the cellular states and genes regulating the NEP fate switch are unknown. Using single-cell RNA sequencing and fate mapping, we defined molecular subtypes of NEPs and their lineages under homeostasis and repair. NEPs contain two major subtypes: astrogliogenic and neurogenic NEPs that are further subdivided based on their location, lineage, and differentiation status. Upon injury, an transitory cellular state arises from BgL-NEPs. Furthermore, mutational analysis revealed that induction of is required for adaptive reprogramming by orchestrating a glial-to-neural switch in vivo following injury. Thus, we provide molecular and cellular insights into context-dependent progenitor plasticity and repair mechanisms in the brain.