Modeling OTUD7A loss-of-function mutation in schizophrenia-associated 15q13.3 microdeletion in human neurons

The edited lines introduced a premature termination at rs757148409/p.Arg89Ter. The mutant iNs showed a ~50% decrease in OTUD7A protein expression without undergoing nonsense-mediated mRNA decay. The mutant iNs also exhibited marked reduction of dendritic complexity, synaptic puncta density of AMPA receptor subunit GluA1 and postsynaptic scaffold PSD-95, as well as neural firing rate and network activity. Congruent with the neural phenotypic alterations in mutant iNs, our transcriptomic analysis showed that the set of OTUD7A LoF downregulated genes was significantly enriched for synapse development and function, and was associated with SZ and other neuropsychiatric disorders. These results suggest that the OTUD7A LoF mutation rs757148409 impairs neurodevelopment and synaptic function in human neurons, providing mechanistic insight into the possible role of OTUD7A in driving neuropsychiatric phenotypes associated with the 15q13.3 microdeletion. Overall design: Identifying causative gene(s) within large genomic regions of copy number variants (CNVs) associated with neuropsychiatric disorders is challenging. Otu deubiquitinase 7a (Otud7a) knockout mice recapitulate some phenotypes associated with the 15q13.3 microdeletion syndrome, leading to the hypothesis that OTUD7A is the driver of this CNV's neuropsychiatric phenotypes. Here, by targeted sequencing of 1,779 SZ cases and 1,418 controls we identified three putative OTUD7A loss-of-function (LoF) mutations in cases, but none in controls. We then modeled one of these OTUD7A LoFs, rs757148409, in human induced pluripotent stem cell (hiPSC)-derived induced excitatory neurons (iNs) by CRISPR/Cas9 engineering.