CRISPRpas: Programmable regulation of alternative polyadenylation by dCas9

ABSTRACT Well over half of human mRNA genes produce alternative polyadenylation (APA) isoforms that differ in mRNA metabolism due to 3’ UTR size changes or have variable coding potentials when coupled with alternative splicing. Aberrant APA is implicated in a growing number of human diseases. A programmable tool for APA regulation, hence, would be instrumental for understanding how APA events impact biological processes. Here, using a catalytically dead Cas9 (dCas9), we developed a method, named CRISPRpas, to alter cleavage and polyadenylation site (PAS) usage in 3’ UTRs or introns. We present key features that facilitate CRISPRpas, including targeting DNA strand, distance between PAS and targeting sequence, and strength of the PAS. For intronic PAS, we additionally analyze strengths of 5’ splice site and target location in intron. Our analyses implicate a dynamic competition between PAS usage and nascent RNA decay when RNA polymerase II elongation is blocked. We show modulation of APA of multiple endogenous genes including a gene that contains a single nucleotide polymorphism (SNP) that affects APA in the human population. CRISPRpas expands the CRISPR toolkit for perturbation of gene expression.