The Year in CRISPRs - 5

Less "Delete,"
More "Copy-Paste" from

CRISPR Gene Editing
C

RISPR, the gene-editing tool that has been
all the rage the past few years, does not
modify the genome as neatly or predictably
as a word processer might alter a document.
Wherever the CRISPR cursor lands in a
mammalian genome, the outcome-a short
deletion or, possibly, a copy-paste-depends on
the relative efficiencies of two different DNA
repair mechanisms. Most often, a CRISPR-induced
double-strand break is repaired via a mechanism
that tends to favor short deletions, limiting
CRISPR's utility as gene-insertion tool. This
repair mechanism, however, can be suppressed,
effectively increasing the efficiency of the other
5

| GENengnews.com

mechanism, the one that may be more
desirable-if the idea is to insert preplanned
genetic modifications.
A means of favoring CRISPR's "copy-paste"
functionality was achieved by scientists at the
Max Delbrück Center for Molecular Medicine
(MDC) Berlin-Buch. They described their
technique March 24 in Nature Biotechnology, in
an article entitled, "Increasing the efficiency of
homology-directed repair for CRISPR-Cas9induced precise gene editing in mammalian cells."
The homology-directed repair (HDR) pathway

enables the insertion of preplanned genetic
modifications using engineered DNA molecules
that share identical sequence regions with the
targeted gene and which are recognized as a
repair template. Thus, HDR repair is very precise
but occurs only at low frequency in
mammalian cells.
The other repair system, called nonhomologous end-joining (NHEJ) is more
efficient in nature but less precise, since it readily
reconnects free DNA ends without repair
template, thereby frequently deleting short
sequences from the genome. Therefore,


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The Year in CRISPRs

Table of Contents for the Digital Edition of The Year in CRISPRs

Contents
The Year in CRISPRs - 1
The Year in CRISPRs - 2
The Year in CRISPRs - 3
The Year in CRISPRs - Contents
The Year in CRISPRs - 5
The Year in CRISPRs - 6
The Year in CRISPRs - 7
The Year in CRISPRs - 8
The Year in CRISPRs - 9
The Year in CRISPRs - 10
The Year in CRISPRs - 11
The Year in CRISPRs - 12
The Year in CRISPRs - 13
The Year in CRISPRs - 14
The Year in CRISPRs - 15
The Year in CRISPRs - 16
The Year in CRISPRs - 17
The Year in CRISPRs - 18
The Year in CRISPRs - 19
The Year in CRISPRs - 20
The Year in CRISPRs - 21
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