Indiscriminate ssDNA cleavage activity of CRISPR-Cas12a induces no detectable off-target effects in mouse embryos.
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ABSTRACT:
SUBMITTER: Wei Y
PROVIDER: S-EPMC8403096 | biostudies-literature | 2021 Sep
REPOSITORIES: biostudies-literature
Publications
Indiscriminate ssDNA cleavage activity of CRISPR-Cas12a induces no detectable off-target effects in mouse embryos.
Wei Yu Y Zhou Yingsi Y Liu Yajing Y Ying Wenqin W Lv Ruiming R Zhao Qimeng Q Zhou Haibo H Zuo Erwei E Sun Yidi Y Yang Hui H Zhou Changyang C
Protein & cell 20210401 9
Similar Datasets
Project description:CRISPR-Cas12a (Cpf1) is a bacterial RNA-guided nuclease that cuts double-stranded DNA (dsDNA) at sites specified by a CRISPR RNA (crRNA) guide. Additional activities have been ascribed to this enzyme in vitro: site-specific (cis) single-stranded DNA (ssDNA) cleavage and indiscriminate (trans) degradation of ssDNA, RNA, and dsDNA after activation by a complementary target. The ability of Cas12a to cleave nucleic acids indiscriminately has been harnessed for many applications, including diagnostics, but it remains unknown if it contributes to bacterial immunity. Here, we provide evidence that cleavage of ssDNA in cis or in trans by Cas12a is insufficient to impact immunity. Using LbCas12a expressed in either Pseudomonas aeruginosa or Escherichia coli, we observed that cleavage of dsDNA targets did not elicit cell death or dormancy, suggesting insignificant levels of collateral damage against host RNA or DNA. Canonical immunity against invasive dsDNA also had no impact on the replicative fitness of co-infecting dsDNA phage, ssDNA phage or plasmid in trans. Lastly, crRNAs complementary to invasive ssDNA did not provide protection, suggesting that ssDNA cleavage does not occur in vivo or is insignificant. Overall, these results suggest that CRISPR-Cas12a immunity predominantly occurs via canonical targeting of dsDNA, and that the other activities do not significantly impact infection outcomes.
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Project description:CRISPR-Cas12a (Cpf1) proteins are RNA-guided enzymes that bind and cut DNA as components of bacterial adaptive immune systems. Like CRISPR-Cas9, Cas12a has been harnessed for genome editing on the basis of its ability to generate targeted, double-stranded DNA breaks. Here we show that RNA-guided DNA binding unleashes indiscriminate single-stranded DNA (ssDNA) cleavage activity by Cas12a that completely degrades ssDNA molecules. We find that target-activated, nonspecific single-stranded deoxyribonuclease (ssDNase) cleavage is also a property of other type V CRISPR-Cas12 enzymes. By combining Cas12a ssDNase activation with isothermal amplification, we create a method termed DNA endonuclease-targeted CRISPR trans reporter (DETECTR), which achieves attomolar sensitivity for DNA detection. DETECTR enables rapid and specific detection of human papillomavirus in patient samples, thereby providing a simple platform for molecular diagnostics.
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Project description:Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas12a is widely used for genome editing and diagnostics, so it is important to understand how RNA-guided DNA recognition activates the cleavage of the target strand (TS) following non-target-strand (NTS) cleavage. Here we used single-molecule magnetic tweezers, gel-based assays and nanopore sequencing to explore DNA unwinding and cleavage. In addition to dynamic and heterogenous R-loop formation, we also directly observed transient double-stranded DNA unwinding downstream of the 20-bp heteroduplex and, following NTS cleavage, formation of a hyperstable 'clamped' Cas12a-DNA intermediate necessary for TS cleavage. Annealing of a 4-nucleotide 3' CRISPR RNA overhang to the unwound TS downstream of the heteroduplex inhibited clamping and slowed TS cleavage by ~16-fold. Alanine substitution of a conserved aromatic amino acid in the REC2 subdomain that normally caps the R-loop relieved this inhibition but favoured stabilisation of unwound states, suggesting that the REC2 subdomain regulates access of the 3' CRISPR RNA to downstream DNA.
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Project description:Cas12a (also called Cpf1) is a representative type V-A CRISPR effector RNA-guided DNA endonuclease, which provides an alternative to type II CRISPR-Cas9 for genome editing. Previous studies have revealed that Cas12a has unique features distinct from Cas9, but the detailed mechanisms of target searching and DNA cleavage by Cas12a are still unclear. Here, we directly observe this entire process by using single-molecule fluorescence assays to study Cas12a from Acidaminococcus sp. (AsCas12a). We determine that AsCas12a ribonucleoproteins search for their on-target site by a one-dimensional diffusion along elongated DNA molecules and induce cleavage in the two DNA strands in a well-defined order, beginning with the non-target strand. Furthermore, the protospacer-adjacent motif (PAM) for AsCas12a makes only a limited contribution of DNA unwinding during R-loop formation and shows a negligible role in the process of DNA cleavage, in contrast to the Cas9 PAM.
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Project description:CRISPR RNAs (crRNAs) that direct target DNA cleavage by Type V Cas12a nucleases consist of constant repeat-derived 5'-scaffold moiety and variable 3'-spacer moieties. Here, we demonstrate that removal of most of the 20-nucleotide scaffold has only a slight effect on in vitro target DNA cleavage by a Cas12a ortholog from Acidaminococcus sp. (AsCas12a). In fact, residual cleavage was observed even in the presence of a 20-nucleotide crRNA spacer moiety only. crRNAs split into separate scaffold and spacer RNAs catalyzed highly specific and efficient cleavage of target DNA by AsCas12a in vitro and in lysates of human cells. In addition to dsDNA target cleavage, AsCas12a programmed with split crRNAs also catalyzed specific ssDNA target cleavage and non-specific ssDNA degradation (collateral activity). V-A effector nucleases from Francisella novicida (FnCas12a) and Lachnospiraceae bacterium (LbCas12a) were also functional with split crRNAs. Thus, the ability of V-A effectors to use split crRNAs appears to be a general property. Though higher concentrations of split crRNA components are needed to achieve efficient target cleavage, split crRNAs open new lines of inquiry into the mechanisms of target recognition and cleavage and may stimulate further development of single-tube multiplex and/or parallel diagnostic tests based on Cas12a nucleases.
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Project description:The CRISPR diagnostic (CRISPR-Dx) technology that employs the trans-cleavage activities has shown great potential in diagnostic sensitivity, specificity, convenience, and portability, and has been recognized as the next-generation diagnostic methods. However, due to the lack of standardized definition of Cas trans-cleavage enzymatic units, it is difficult to standardize the present CRISPR-Dx systems, which have undoubtedly impeded the development of the CRISPR-Dx industry. To solve the problem, we here first systematically optimized the reaction systems for Cas12a, and then defined its trans-cleavage units (transU), which we believe will be of great importance and interest to researchers in both molecular diagnostic industry and basic research. Moreover, a simple protocol was provided to facilitate a step-by-step measurement of the Cas12a transU, which can also act as a reference for the definition of the transU for other Cas proteins.
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Project description:Cas12a is a type V-A CRISPR-Cas RNA-guided endonuclease. It cleaves dsDNA at specific site, and then is activated for nonspecific ssDNA cleavage in trans in vitro. The immune function of the trans activity is still unknown. To address this question, we constructed a Cas12a targeting system in Escherichia coli, where Cas12a cleaved a high-copy target plasmid to unleash the trans ssDNA cleavage activity. Then, we analyzed the effect of the Cas12a targeting on a non-target plasmid and a ssDNA phage. The results show that Cas12a efficiently eliminates target plasmid but exerts no impact on the maintenance of the non-target plasmid or plague formation efficiency of the phage. In addition, a two-spacer CRISPR array, which facilitates target plasmid depletion, still has no detectable effect on the non-target plasmid or phage either. Together, the data suggest that the trans ssDNA cleavage of Cas12a does not contribute to immunity in vivo.
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