gene editing: from biblical times to the present klaus rajewsky max-delbrück-center for molecular...
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Gene editing: From biblical times to the present
Klaus Rajewsky
Max-Delbrück-Center for Molecular Medicine, Berlin
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• ~4000 years ago: Breeding of domestic animals Jacob (Genesis 30, 43)
• 1866 Inheritance of specific traits and their segregation in germ cells Gregor Mendel
• 1870-1902 Discovery of Chromosomes Walter Flemming, Eduard van Beneden, Walter S. Sutton and others
• 1900: Rediscovery of Mendel’s laws of inheritance Hugo de Vries and Karl Ehrich Correns
• Gene mutations as drivers of evolution Hugo De Vries (plants); T.H. Morgan, J. Muller (flies)
Historical milestones towards gene editing I
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• 1944 DNA as the carrier of genetic information Oswald T. Avery, Colin MacLeod & Maclyn McCarty
• 1953 The DNA double helix Duplication of DNA James D. Watson & Francis Crick
• 1961-1968: The genetic triplet code and its translation into the amino acid sequence of proteins (the “Central Dogma”). Control of gene expression. • Since 1972: Recombinant DNA technology, mapping and sequencing of genes and genomes. Transgenesis.
• 1984-2003: The Human Genome Project
Historical milestones towards gene editing II
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• 1944 DNA as the carrier of genetic information Oswald T. Avery, Colin MacLeod & Maclyn McCarty
• 1953 The DNA double helix Duplication of DNA James D. Watson & Francis Crick
• 1961-1968: The genetic triplet code and its translation into the amino acid sequence of proteins (the “Central Dogma”). Control of gene expression.• Since 1972: Recombinant DNA technology, mapping and sequencing of genes and genomes. Transgenesis.
• 1984-2003: The Human Genome Project
-> Gregor Mendel’s “cell elements” now understood at the molecular level!
Historical milestones towards gene editing II
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The human genome: A 2-meter DNA filament organized
into chromosomes, with ~25,000 genes
Cell
Cell nucleus1/1000 mm
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Primary RNA
Exon Intron
mRNA
PGene (DNA)
ProteinThe DNA Double Helix
The Central Dogma
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Genes and gene expression
• Each gene encodes a particular protein.
• Each cell in our organism contains the complete genome, but different cell types express different patterns of genes.
The function of cells depends on an intact pattern of protein expression.
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Mutations:
• Change the base sequence of genes• Disturb protein function• Occur spontaneously or• Are caused by environmental cues
Most mutations are repaired by the cell!
Insufficient repairCell damage, cancer, inherited diseases
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Inherited diseases
Caused by gene mutations, transmitted through the germ line from
generation to generation.Inherited diseases can be mono- or
polygenic.
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How can we intentionally mutate or repair genes in the
genome?
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?
How to “find” a gene?
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ACC
TGGTCAAACGGCTAG
If one knows the base sequence…
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ACC
T-AG-CG-CT-AC-GA-TA-TA-TC-GG-CG-CC-GT-AAG
…through a DNA of complementary base sequence!
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Gene targeting:
Targeting Vector (DNA)
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Target gene
Mutant gene
Targeting vector
Homology arm Homology arm
RecombinationRecombination
Target gene and mutant gene find each other through base complementarity; this is occasionally followed by substitution of the target gene by the mutant gene through a process called recombination.
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Mutant gene
Gene substitution by a mutant gene
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Classical gene targeting in mouse embryonic stem (ES)
cells
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Each cell of this “inner cell mass” can give rise to a complete mouse. As embryonic stem (ES) cells they can be propagated in cell culture indefinitely.
Blastocyst
Mouse embryonic development and embryonic stem (ES) cells
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Classical gene targeting in the mouse
From Capecchi M.1994, with modifications
Oliver Smithies, Mario Capecchi, Martin Evans
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Recombinase-assisted targeted mutagenesis
Conditional gene targeting
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Cre
Cre
Cre is a bacteriophage-derived enzyme which binds paired DNA target sequences called loxP and excises the DNA between
them – also in mammalian cells
Brian Sauer, Heiner Westphal, Jamey Marth
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Conditional gene targeting: The Cre Zoo 1996
LoxP-flanked, fully active target gene
Target gene specificallydeleted in a particular cell type
Cell-type specificCre transgenes
From Rajewsky, K. et al. 1996, with modifications
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Conditional gene targeting: The Cre Zoo 1996
Allows gene editing in somatic cells in vivo
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Classical gene targeting is a very inefficient process because of the low frequency of spontaneous recombination.
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Classical gene targeting is a very inefficient process because of the low frequency of spontaneous recombination.
But the rate of recombination can be dramatically increased by the introduction of a DNA break in the target gene!
Initiation of cellular DNA repair
Rouet, Smih & Jasin 1994Puchta, Dujon & Hohn 1993
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Target gene
Non-homologous end joining: Gene inactivation
Homology with an added donor template: Gene correction
DNA break
Repair of a DNA double strand break with two
different possible outcomes
*
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Two pathways of repair of a DNA double strand break
Gene Inactivation
Precise gene modification
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Since then: Search for and engineering of sequence-specific DNA nucleases
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Since then: Search for and engineering of sequence-specific DNA nucleases
Meganucleases, Zinc finger nucleases, TALE nuclease fusions,
And finally:
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The CRISPR/Cas9 system:
Cas9 is a bacterial DNA nuclease associated with a guide RNA that docks the nuclease to a target gene through base complementarity.
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The CRISPR/Cas9 system:
Cas9 is a bacterial DNA nuclease associated with a guide RNA that docks the nuclease to a target gene through base complementarity.The base sequence of the guide RNA can be freely chosen, therefore the nuclease can be targeted to any target gene in the genome.
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Target gene
Repair through non-homologous end joining:Gene inactivation
Repair through homology with a donor template: Gene repair
+ +
Guide-RNA allows the introduction of specific DNA breaks
CRISPR/Cas9 finds and cuts (almost) any
target gene in mammalian cells!
DNA break*
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Where to go with this amazingly efficient technology in the human?
.
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Where to go with this amazingly efficient technology in the human?
We have become masters in the art of manipulating genes, but our
understanding of their function and interaction is far more limited.
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Where to go with this amazingly efficient technology in the
human?