Cas13d-mediated isoform-specific RNA knockdown with a unified computational and experimental toolbox [Screen]

Alternative splicing is an essential mechanism for diversifying proteins, with different mature RNA isoforms producing different proteins with potentially distinct functions. Two major challenges in characterizing the cellular function of isoforms are the lack of both experimental methods to specifically and efficiently modulate isoform expression and computational tools for complex experimental design. To address these gaps, we developed and methodically tested a strategy which pairs the RNA-targeting CRISPR/Cas13d system with guide RNAs (gRNAs) that overlap exon-exon junctions in the mature RNA. We perform a high-throughput essentiality screen, numerous qPCR assays, and PacBio long read sequencing to affirm that our strategy works to specifically target the unique junctions of isoforms to robustly knockdown their RNA. In parallel, we provide computational tools for experimental design and screen analysis. Considering all possible splice junctions in current GENCODE annotations and our predictions of gRNA efficacy, we estimate that this strategy can target 94% of all human isoforms, including 29,238 protein-coding and 9,638 lncRNA isoforms that are specifically targetable with a gRNA spanning a unique splice junction. Overall design: Essentiality screen in an A375 monoclonal Cas13d-expressing cell line