The Year in CRISPRs - 6

The Year in CRISPRs * Less "Delete," More "Copy-Paste" from CRISPR Gene Editing

NHEJ repair can only be used to create short
genomic deletions, but does not support
precise gene modification or the insertion
and replacement of gene segments.
The MDC researchers succeeded in
increasing the efficiency of the more precisely
working HDR repair system by temporarily
inhibiting the most dominant repair protein
of NHEJ, the enzyme DNA Ligase IV. In their
approach, they used various inhibitors such as
proteins and small molecules. They also used
what MDC researcher Ralf Kühn, Ph.D., called a
"trick of nature"-the suppression of Ligase IV
with the proteins of adeno viruses.
"We suppressed the NHEJ key molecules
KU70, KU80 or DNA ligase IV by gene silencing,

| GENengnews.com

the ligase IV inhibitor SCR7 or the co-expression
of adenovirus 4 E1B55K and E4orf6 proteins in a
'traffic light' and other reporter systems," wrote
the authors of the Nature Genetics article.
"Suppression of KU70 and DNA ligase IV promotes
the efficiency of HDR four- to fivefold. When
co-expressed with the Cas9 system, E1B55K and
E4orf6 improved the efficiency of HDR up to
eightfold and essentially abolished NHEJ activity
in both human and mouse cell lines."
CRISPR technology is already used in the
laboratory to correct genetic defects in mice.
Researchers also plan to modify the genetic set
up of induced pluripotent stem cells (iPS), which
can be differentiated into specialized cell types
or tissues. That is, researchers are able to use the
new tool to introduce patient-derived mutations

into the genome of iPS cells for studying the
onset of human diseases. "Another future goal,
however, is to use CRISPR for somatic gene
therapy in humans with severe diseases," MDC
researcher Klaus Rajewsky, M.D., pointed out.
Dr. Rajewsky added that the new capabilities
to precisely edit the genome have sparked off
an intense debate in the United States and elsewhere, since the new precision tools could also
be applied to modifying the genome in human
germ cells or embryos. Although manipulation of
the human germline is prohibited by law in many
countries, including Germany, a global ban is not
in effect. The MDC researchers are fascinated by
the new opportunities the CRISPR-Cas9 system
offers for biomedical research, but strictly reject
genetic modification of the human germline. n

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The Year in CRISPRs

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