(RNA-seq-SHSY5Y) Hao-Fountain syndrome protein USP7 mediates neuronal differentiation via BCOR-ncPRC1.1

Pathogenic variants of ubiquitin-specific protease 7 (USP7) cause the neurodevelopmental disorder Hao-Fountain syndrome. However, which of its pleiotropic substrates are relevant for neurodevelopment has remained unclear. Here, we present a combination of quantitative proteomics, transcriptomics and epigenomics to define the core USP7 circuitry during neurodifferentiation. USP7 activity is required for the transcriptional programs that direct the differentiation of human ESCs to neural stem cells, and neuronal differentiation of SHSY5Y neuroblastoma cells. In addition to other substrates, including TRIM27, USP7 controls the dosage of the Polycomb H2AK119ub1 ubiquitin ligases ncPRC1.1 and ncPRC1.6. We found that BCOR-ncPRC1.1, but not ncPRC1.6 or TRIM27, is a key effector of USP7-dependent neuronal differentiation. Indeed, BCOR-ncPRC1.1 mediates the majority of USP7-dependent gene regulation during this process. Besides providing a detailed map of the USP7 regulome during neuronal differentiation, our results suggest that Hao-Fountain syndrome and ncPRC1.1-associated neurodevelopmental disorders involve dysregulation of a shared epigenetic network.