Project description:CRISPR-based gene perturbation enables unbiased investigations of single and combinatorial genotype-to-phenotype associations. In light of efforts to map combinatorial gene dependencies at scale, choosing an efficient and robust CRISPR-associated (Cas) nuclease is of utmost importance. Even though SpCas9 and AsCas12a are widely used for single, combinatorial, and orthogonal screenings, side-by-side comparisons remain sparse. Here, we systematically compared combinatorial SpCas9, AsCas12a, and CHyMErA in hTERT-immortalized retinal pigment epithelial cells and extracted performance-critical parameters for combinatorial and orthogonal CRISPR screens. Our analyses identified SpCas9 to be superior to enhanced and optimized AsCas12a, with CHyMErA being largely inactive in the tested conditions. Since AsCas12a contains RNA processing activity, we used arrayed dual-gRNAs to improve AsCas12a and CHyMErA applications. While this negatively influenced the effect size of combinatorial AsCas12a applications, it enhanced the performance of CHyMErA. This improved performance, however, was limited to AsCas12a dual-gRNAs, as SpCas9 gRNAs remained largely inactive. To avoid the use of hybrid gRNAs for orthogonal applications, we engineered the multiplex SpCas9-enAsCas12a system (multiSPAS) that avoids RNA processing for efficient orthogonal gene editing.
Project description:We report the PAMs of AsCas12a using a cell-free TXTL-based cleavage assay. By adding randomized PAM library and AsCas12a-gRNA in vitro, functional PAM sequences were cleaved, while non-functional PAMs remained. By amplifying the non-cleaved DNA, we use next-generation sequencing to analyze the depletion of functional PAMs of AsCas12a.
2019-01-01 | GSE123443 | GEO
Project description:Test the editing efficiency of AsCas12a and SpCas9 in different settings
Project description:we characterized a novel compact Cas12a ortholog, EbCas12a, from the Erysipelotrichia bacterium with activities in mammalian cells. It is with the PAM sequence of 5’-TTTV-3’ (V=A, G, C) and the smallest size of ~3.47kb among reported Cas12a orthologs so far. Moreover, enhanced EbCas12a (enEbCas12a) was also developed to have comparable editing efficiency with higher specificity to AsCas12a and LbCas12a in mammalian cells. With the help of the compact enEbCas12a, all-in-one AAV delivery system with crRNA for Cas12a was developed for both in vitro and in vivo. Altogether, with the help of the novel smallest high fidelity enEbCas12a, this first case of the all-in-one AAV delivery for Cas12a could greatly boost future gene therapy and scientific research.
Project description:RNA base editing represents a promising alternative for genome editing. Recent approaches harness the endogenous RNA editing enzyme ADAR to circumvent problems related to the ectopic expression of an editing enzyme, but they suffer from sequence restriction, lack of efficiency, and bystander editing. Here, we present in‐silico optimized CLUSTER guide RNAs, which bind their target mRNAs in a multivalent fashion and thereby enable editing with unprecedented precision as shown by next generation sequencing. CLUSTER guide RNAs can be genetically encoded and manufactured into viruses to work in various cell lines. They achieve on‐target editing on endogenous transcripts like GUSB and NUP43 with yields up to 45% without bystander editing and have been shown to recruit endogenous ADAR in vivo. The CLUSTER approach tremendously enlarges the sequence space available for guide RNA design and opens new avenues for drug development in the field of RNA base editing.
2021-09-20 | GSE184244 | GEO
Project description:Next Generation Sequencing data of HAP1 cells after genome editing with AsCas12a or SpCas9
Project description:We present a strategy to investigate regulatory elements that leverages programmable reagents to selectively inactivate their endogenous chromatin state. The reagents, which comprise fusions between transcription activator- like effector (TALE) repeat domains and the LSD1 histone demethylase, efficiently remove enhancer-associated chromatin modifications from target loci, without affecting control regions. We find that inactivation of enhancer chromatin by these fusions frequently causes down- regulation of proximal genes. Our study demonstrates the potential of 'epigenome editing' tools to characterize a critical class of functional genomic elements. ChIP-seq analysis of TALE-Fusion Proteins
Project description:Gene editing was used to modify an endogenous allele of USP13 in human HCT116 cells with the addition of a 1X FLAG/Streptavidin Binding Peptide dual epitope tag. Nuclear lysates were prepared and dual affinity purification was performed. Then, GelC/MS/MS was performed to identify proteins that were present after dual affinity purification from dual epitope-tagged cells but not from dual affinity purification from untagged parental cells.