Poison exon splicing in the human brain: a new frontier for understanding and targeting neurological disorders

Abstract

BackgroundPoison exons (PE) are highly conserved exons whose inclusion creates premature termination codons (PTCs) and triggers nonsense-mediated decay (NMD) of the mature transcript. Despite their important role in post-transcriptional regulation, PEs remain poorly annotated due to the lack of systematic transcriptome-wide approaches. ResultsA comparative analysis of 957 eukaryotic transcriptomes revealed that Homo Sapiens exhibits the highest enrichment of NMD-targeted isoforms. By systematically predicting and annotating splicing events that generate PTCs, we found 9,814 PEs in the human genome. Using RNA-seq dataset from GTEx and BrainSpan, we analyzed PE splicing across tissues and developmental stages and identified 83 PEs uniquely found in the human brain, 973 PEs with brain-specific differential splicing, and 1,284 PEs differentially spliced during brain development. By integrating ClinVar variant annotations with SpliceAI predictions, we identified 1,625 pathogenic variants associated with neurological disorders that are predicted to affect the splicing of 743 PEs, and we functionally validated the impact of a subset of them using CRISPR prime-editing in human cells. Functional characterization of the deep intronic NDUFAF6 c.420+784C>T variant associated with Leigh syndrome demonstrated increased PE inclusion and a significant reduction in NDUFAF6 protein levels in iPSC-derived induced neurons. Mutant cells also exhibited impaired mitochondrial membrane potential compared to controls. Together, these findings provide functional evidence that the c.420+784C>T variant promotes aberrant PE inclusion, leading to reduced NDUFAF6 expression and mitochondrial dysfunction. ConclusionsOur findings highlight PEs as pivotal regulators of gene expression in the human brain and support the therapeutic targeting of PE splicing in neurological diseases.