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Research method

CRISPR-Cas9 Genome Editing

9 studies

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CRISPR in this library is two different objects that share a name. In bacteria it is an adaptive immune array of repeats and spacers; papers can catalogue those arrays without editing anything. In experimental cells and plants it is a programmable nuclease or RNA-targeting enzyme (Cas9, dCas9, Cas13a) used to cut, bind, or interfere with a chosen sequence. The student question 'what is CRISPR?' therefore has to ask which of those jobs the paper actually did.

Researchers reach for Cas enzymes when they need a targeted cut, a promoter pull-down, or sequence-specific viral interference; they reach for CRISPR-array scans when they are describing prokaryotic genomes. The method answers either 'what happens if we target this sequence?' or 'where are these arrays and what might they fold into?' Mixing those answers is the characteristic mistake this page exists to prevent. Native-array papers do not demonstrate genome editing; Cas-tool papers do not, by themselves, map every CRISPR locus in nature.

Studies

9

Findings

4

7 supporting · 0 challenging · 0 qualifying citations

Open tensions

2

Currently

What we know

  1. Native CRISPR arrays can be studied as sequence and predicted RNA structure without any editing experiment. A scan of 439 genomes found 561 arrays in 195 genomes; some repeat clusters had consistently high folding potential, taken as support for RNA intermediates — computational structure, not a Cas9 knockout.
  2. Cas13a can be programmed as an antiviral in plants. Targeting different TuMV genomic regions reduced GFP and viral accumulation, showing sequence-specific RNA-virus interference rather than a DNA double-strand break. Guide choice still mattered, and the paper is not a field deployment against all RNA viruses.
  3. Catalytically dead Cas9 can be used as a locus-specific hook. dCas9 chromatin immunoprecipitation (CasIP) in MDA-MB231 cells pulled RNAs at the FLI1 promoter and helped identify FECR1, a FLI1 exonic circRNA that activates FLI1 and promotes invasion — a dCas9 affinity experiment, not a knockout screen.
  4. Many papers in the CRISPR index mention CRISPR or Cas proteins in passing while the actual experiment is something else (APEX2 proximity labelling, pan-genome presence/absence, ChIP-seq of histone acylations, scRNA-seq of endoderm). Those hits show why a body-count lexicon over-recruits; they are not additional editing results.

Largest unresolved question

The strongest tension is naming. The 2007 array paper and the Listeria pan-genome treat CRISPR as a genomic feature of bacteria; the Cas13a and dCas9 papers treat CRISPR–Cas as a laboratory tool. Both usages are historically connected, but a finding about repeat RNA folding does not license a claim about editing a human promoter, and a CasIP result does not catalogue environmental CRISPR diversity.

Procedure

How it works

The main stages of the method. Specific protocols and analysis choices vary between studies.

  1. Decide whether the object is an array or a tool

    In bacteria, CRISPR is a repeat-spacer immune array that can be catalogued without editing anything. In experimental cells and plants it is a programmable Cas enzyme. Mixing those jobs is the characteristic mistake this page exists to prevent.

  2. Catalogue native arrays, or programme an enzyme

    Array papers scan genomes for repeats, spacers, and predicted RNA folds. Tool papers load Cas9, dCas9, or Cas13a with a guide against a chosen sequence. Computational folding potential is not direct RNA-structure proof for every array.

  3. Cut, bind, or interfere at the target

    Cas9 can make a DNA double-strand break; dCas9 can bind without cutting; Cas13a can interfere with an RNA virus. Calling every experiment a knockout is false for this set.

  4. Score the intended molecular outcome

    Editing papers report a mutant allele, a promoter pull-down, or reduced viral GFP. Native-array papers report where arrays sit and what they might fold into. Those are not interchangeable results.

  5. Do not read an array catalogue as a knockout

    CRISPR answers either what happens if this sequence is targeted, or where these arrays are. Native-array papers do not demonstrate genome editing; a Cas13a GFP drop in plants is sequence-specific interference, not a field antiviral for any RNA virus.

Common misconceptions

  • CRISPR in a paper always means the authors knocked out a gene with Cas9.

    In this library CRISPR often means a bacterial repeat-spacer array (439 genomes, 561 arrays) or a non-cutting tool (dCas9 CasIP, Cas13a RNA interference). Gene knockout and knockdown is a separate method page when loss-of-function is actually what was done.

  • If Cas13a reduces viral GFP in plants, CRISPR is ready as a field antiviral for any RNA virus.

    Interference depended on which TuMV region was targeted; the paper does not demonstrate deployment across viruses or environments.

  • Computational folding of CRISPR repeats proves those RNAs exist and function in the cell.

    The 2007 paper reports folding-potential scores across clusters as support for RNA intermediates, and explicitly is not direct RNA-structure proof for every array.

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