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Phage-mediated delivery of CRISPR payloads.
Over the past decade, improvements in sequencing technologies and computational tools have advanced our understanding of the composition and function of microbial communities in various environments. Now, in order to manipulate and engineer these communities, we need technologies that enable broadly applicable and specific alterations to establish and modulate the molecular basis for their functional roles. Recent advances in bacteriophage engineering strategies, synthetic biology techniques, and in silico approaches have greatly expanded our ability to perform in situ perturbations. Clustered regularly interspaced short palindromic repeats-Cas systems in particular can provide an efficient means of engineering phages, and can also be delivered as a recombinant payload to perform precision genome editing directly in the host environment. Modified Cas effectors have been developed that allow for increasingly diverse edits with applications in the fields of medicine, food, and agriculture. In this review, we discuss recent advances in using bacteriophages to deliver various clustered regularly interspaced short palindromic repeats-Cas effectors. While challenges remain regarding the phylogenetic breadth of deployment, recombinant phages generally present a unique and effective means to rationally engineering microbial community function and composition.
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CRISPR's Twisted Tales: Clarifying Misconceptions about Heritable Genome Editing.
The raging controversy about whether heritable genome editing should be permitted is shaped and structured by the prevailing and countervailing narratives in circulation. In recent years, considerable shortcomings have come to characterize this discourse; it is now time to identify and correct a number of serious misunderstandings and distortions that have taken hold. This essay begins by briefly evaluating reactions to the November 2018 announcement that gene-edited babies had been born; it asserts that widespread agreement about the researcher's recklessness and dire ethical violations concealed deep fault lines among participants in the heritable genome editing debate. It goes on to consider several key omissions and misrepresentations that distort public understanding and undermine genuine debate. It suggests that the conversation must be refocused away from technical, medical, and scientific considerations toward matters of societal meanings, values, context, and consequences. It concludes with criteria for a broadly inclusive and meaningful decision-making process about whether heritable genome editing has any place in the shared and just future to which we aspire.
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Meeting Report: German Genetics Society-Genome Editing with CRISPR.
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CRISPR-mediated Transfection of Brugia malayi.
The application of reverse genetics in the human filarial parasites has lagged due to the difficult biology of these organisms. Recently, we developed a co-culture system that permitted the infective larval stage of Brugia malayi to be transfected and efficiently develop to fecund adults. This was exploited to develop a piggyBac transposon-based toolkit that can be used to produce parasites with transgene sequences stably integrated into the parasite genome. However, the piggyBac system has generally been supplanted by Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) based technology, which allows precise editing of a genome. Here we report adapting the piggyBac mediated transfection system of B. malayi for CRISPR mediated knock-in insertion into the parasite genome. Suitable CRISPR insertion sites were identified in intergenic regions of the B. malayi genome. A dual reporter piggybac vector was modified, replacing the piggyBac inverted terminal repeat regions with sequences flanking the insertion site. B. malayi molting L3 were transfected with a synthetic guide RNA, the modified plasmid and the CAS9 nuclease. The transfected parasites were implanted into gerbils and allowed to develop into adults. Progeny microfilariae were recovered and screened for expression of a secreted luciferase reporter encoded in the plasmid. Approximately 3% of the microfilariae were found to secrete luciferase; all contained the transgenic sequences inserted at the expected location in the parasite genome. Using an adaptor mediated PCR assay, transgenic microfilariae were examined for the presence of off target insertions; no off-target insertions were found. These data demonstrate that CRISPR can be used to modify the genome of B. malayi, opening the way to precisely edit the genome of this important human filarial parasite.
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Base editing-mediated perturbation of endogenous PKM1/2 splicing facilitates isoform-specific functional analysis in vitro and in vivo.
OBJECTIVES: PKM1 and PKM2, which are generated from the alternative splicing of PKM gene, play important roles in tumourigenesis and embryonic development as rate-limiting enzymes in glycolytic pathway. However, because of the lack of appropriate techniques, the specific functions of the 2 PKM splicing isoforms have not been clarified endogenously yet. MATERIALS AND METHODS: In this study, we used CRISPR-based base editors to perturbate the endogenous alternative splicing of PKM by introducing mutations into the splicing junction sites in HCT116 cells and zebrafish embryos. Sanger sequencing, agarose gel electrophoresis and targeted deep sequencing assays were utilized for identifying mutation efficiencies and detecting PKM1/2 splicing isoforms. Cell proliferation assays and RNA-seq analysis were performed to describe the effects of perturbation of PKM1/2 splicing in tumour cell growth and zebrafish embryo development. RESULTS: The splicing sites of PKM, a 5' donor site of GT and a 3' acceptor site of AG, were efficiently mutated by cytosine base editor (CBE; BE4max) and adenine base editor (ABE; ABEmax-NG) with guide RNAs (gRNAs) targeting the splicing sites flanking exons 9 and 10 in HCT116 cells and/or zebrafish embryos. The mutations of the 5' donor sites of GT flanking exons 9 or 10 into GC resulted in specific loss of PKM1 or PKM2 expression as well as the increase in PKM2 or PKM1 respectively. Specific loss of PKM1 promoted cell proliferation of HCT116 cells and upregulated the expression of cell cycle regulators related to DNA replication and cell cycle phase transition. In contrast, specific loss of PKM2 suppressed cell growth of HCT116 cells and resulted in growth retardation of zebrafish. Meanwhile, we found that mutation of PKM1/2 splicing sites also perturbated the expression of non-canonical PKM isoforms and produced some novel splicing isoforms. CONCLUSIONS: This work proved that CRISPR-based base editing strategy can be used to disrupt the endogenous alternative splicing of genes of interest to study the function of specific splicing isoforms in vitro and in vivo. It also reminded us to notice some novel or undesirable splicing isoforms by targeting the splicing junction sites using base editors. In sum, we establish a platform to perturbate endogenous RNA splicing for functional investigation or genetic correction of abnormal splicing events in human diseases.
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Playing God? Media coverage of CRISPR in the United States.
Announcements in 2017 and 2018 that scientists used a gene editing technique called Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) to permanently alter human embryos have highlighted the urgency in regulating the technology's ethical, political, and legal implications. To better understand how a regulatory regime might evolve in response to CRISPR, we must examine how the media covers it. This article reviews online and television news sources in the United States to determine the tone, content, and frequency in media coverage of CRISPR. We find that coverage remained ambiguous and infrequent, as scientific research into CRISPR's clinical potential for treating human disease surged. This infrequent coverage indicates that the media have not yet established the salience of CRISPR to a degree that engages the public or policymakers, though the issue will continue to gain importance as CRISPR transitions from experimental efforts into clinical practice.
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CRISPR-mediated multiplexed genetic manipulation.
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China's CRISPR revolution.
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Applications of CRISPR Technologies Across the Food Supply Chain.
The food industry faces a 2050 deadline for the advancement and expansion of the food supply chain to support the world's growing population. Improvements are needed across crops, livestock, and microbes to achieve this goal. Since 2005, researchers have been attempting to make the necessary strides to reach this milestone, but attempts have fallen short. With the introduction of clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) proteins, the food production field is now able to achieve some of its most exciting advancements since the Green Revolution. This review introduces the concept of applying CRISPR-Cas technology as a genome-editing tool for use in the food supply chain, focusing on its implementation to date in crop, livestock, and microbe production, advancement of products to market, and regulatory and societal hurdles that need to be overcome.
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Editor's cut: DNA cleavage by CRISPR RNA-guided nucleases Cas9 and Cas12a.
Discovered as an adaptive immune system of prokaryotes, CRISPR-Cas provides many promising applications. DNA-cleaving Cas enzymes like Cas9 and Cas12a, are of great interest for genome editing. The specificity of these DNA nucleases is determined by RNA guides, providing great targeting adaptability. Besides this general method of programmable DNA cleavage, these nucleases have different biochemical characteristics, that can be exploited for different applications. Although Cas nucleases are highly promising, some room for improvement remains. New developments and discoveries like base editing, prime editing, and CRISPR-associated transposons might address some of these challenges.
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