Randomized PAM depletion of phylogenetically-diverse Cas12a nucleases
Ontology highlight
ABSTRACT:
PROVIDER: PRJNA539942 | ENA |
REPOSITORIES: ENA
Dataset's files
| Action | DRS | |||
|---|---|---|---|---|
| SRR8978750.fastq.gz | Fastqsanger.gz | |||
| SRR8978760.fastq.gz | Fastqsanger.gz | |||
| SRR8978751.fastq.gz | Fastqsanger.gz | |||
| SRR8978761.fastq.gz | Fastqsanger.gz | |||
| SRR8978752.fastq.gz | Fastqsanger.gz |
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Project description:We report the PAMs of phylogenetically-diverse Cas12a nucleases using a cell-free TXTL-based PAM screen. By adding a 5N randomized PAM library and Cas12a-gRNA in vitro, recognized PAM sequences were cleaved, while non-recognized PAMs remained. By amplifying the non-cleaved DNA, we used next-generation sequencing to analyze the depletion of functional PAMs of these Cas12a nucleases.
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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.
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Project description:We report the PAMs of NmeCas9 using a cell-free TXTL-based cleavage assay. By adding randomized PAM library and NmeCas9-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 NmeCas9.
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Project description:Randomized PAM depletion of AsCas12a
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Project description:CRISPR-Cas systems comprise diverse adaptive immune systems in prokaryotes whose RNA-directed nucleases have been co-opted for various technologies. Recent efforts have focused on expanding the number of known CRISPR-Cas subtypes to identify nucleases with novel properties. However, the functional diversity of nucleases within each subtype remains poorly explored. Here, we used cell-free transcription-translation systems and human cells to characterize six Cas12a single-effector nucleases from the V-A subtype, including nucleases sharing high sequence identity. While these nucleases readily utilized each other's guide RNAs, they exhibited distinct PAM profiles and apparent targeting activities that did not track based on phylogeny. In particular, two Cas12a nucleases encoded by Prevotella ihumii (PiCas12a) and Prevotella disiens (PdCas12a) shared over 95% amino-acid identity yet recognized distinct PAM profiles, with PiCas12a but not PdCas12a accommodating multiple G's in PAM positions -2 through -4 and T in position -1. Mutational analyses transitioning PiCas12a to PdCas12a resulted in PAM profiles distinct from either nuclease, allowing more flexible editing in human cells. Cas12a nucleases therefore can exhibit widely varying properties between otherwise related orthologs, suggesting selective pressure to diversify PAM recognition and supporting expansion of the CRISPR toolbox through ortholog mining and PAM engineering.
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Project description:Because of their smallness, the recently developed CRISPR-Cas12f nucleases can be effectively packaged into adeno-associated viruses for gene therapy. However, a systematic evaluation of the editing outcomes of CRISPR-Cas12f is lacking. In this study, we apply a high-throughput sequencing method to comprehensively assess the editing efficiency, specificity, and safety of four Cas12f proteins in parallel with that of Cas9 and two Cas12a proteins at multiple genomic sites. Cas12f nucleases achieve robust cleavage at most of the tested sites and mainly produce deletional fragments. In contrast, Cas9 and Cas12a show relatively higher editing efficiency at the vast majority of the tested sites. However, the off-target hotspots identified in the Cas9- and Cas12a-edited cells are negligibly detected in the Cas12f-edited cells. Moreover, compared to Cas9 and Cas12a nucleases, Cas12f nucleases reduce the levels of chromosomal translocations, large deletions, and integrated vectors by 2- to 3-fold. Therefore, our findings confirm the editing capacity of Cas12f and reveal the ability of this nuclease family to preserve genome integrity during genome editing.
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Project description:Systematic mapping of genetic interactions and interrogation of the functions of sizeable genomic segments in mammalian cells represent important goals of biomedical research. To advance these goals, we present a CRISPR-based screening system for combinatorial genetic manipulation that employs co-expression of Cas9 and Cas12a nucleases and machine learning-optimized libraries of hybrid Cas9-Cas12a guide RNAs. This system, named CHyMErA (Cas Hybrid for Multiplexed Editing and Screening Applications), outperforms genetic screens using Cas9 or Cas12a editing alone. Application of CHyMErA to the ablation of mammalian paralog gene pairs reveals extensive genetic interactions and uncovers phenotypes normally masked by functional redundancy. Application of CHyMErA in a chemo-genetic interaction screen identifies genes that impact cell growth in response to mTOR pathway inhibition. Moreover, by systematically targeting thousands of alternative splicing events, CHyMErA identifies exons underlying human cell line fitness. CHyMErA thus represents an effective screening approach for genetic interaction mapping and the functional analysis of sizeable genomic regions, such as alternative exons.
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