Znhit3 regulates p53/p21 signaling and governs cerebellar granule cell development.

Mutations in ZNHIT3 are strongly associated with progressive encephalopathy with edema, hypsarrhythmia and optic atrophy (PEHO syndrome), characterized by severe cerebellar atrophy and profound intellectual disability; however, their role in cerebellar development remains unknown. By developing spatiotemporally-regulated conditional Znhit3 knockout mice, we discovered that Znhit3 is essential for granule cell progenitor survival, proliferation, differentiation, and migration. Knockout of Znhit3 caused loss of granule cell progenitors due to apoptosis, premature cell-cycle exit, and migration arrest and resulted in progressive anterior-lobe atrophy and motor deficits. The granule cell progenitor-autonomous defects secondarily impaired Purkinje cell alignment, dendritic maturation, and synaptic organization. Transcriptomic analyses revealed activation of the p53/p21 pathway, rRNA processing defects, and nucleolar stress. Genetic or pharmacologic inhibition of p53/p21 signaling rescued granule cell progenitor development and restored cerebellar architecture in the Znhit3-knockout mice. Thus, ZNHIT3 is a critical regulator of ribosome biogenesis and cerebellar growth, suggesting nucleolar stress-p53/p21 signaling as a potential therapeutic target in ZNHIT3-related disorders.