Unit 5: Gene Editing And CRISPR Flashcards
(37 cards)
*What is gene editing?
Modifications directed at the genome, their contexts (epigenetic marks) or their results (transcripts) using endonuclease
Endonuclease=enzyme that cuts DNA
*What was the previous technology used for gene editing?
Recombinant DNA
*What gene editing tools do we use now?
- Zinc Finger Nucleases (ZFNs): High cost + difficulty, operating problems
- Transcription Activator-Like Effector Nucleases (TALENs): More difficult + expensive than CRISPR
- CRISPR-Cas
*What is CRISPR-Cas?
- It is a natural defence system against viruses in bacteria + archaea
- CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats
- Cas: CRISPR-associated
What are the stages of the natural system CRISPR-Cas was found in?
Accquisition, expression + interference
See diagram of how/where pg.6
Who was the Spanish scientist involved in the discovery of CRISPR?
Francisco Martínez Mojica
*Who won the Nobel Prize in Chemistry in 2020?
- Emmanuelle Charpentier + Jennifer A. Doudna
- “for the development of a method of genome editing
Who did Charpentier + Doudna fight over ownership of use of CRISPR-Cas with?
-Feng Zhang
*What is Germinal genetic modification?
In *reproductive cells (sperm + egg) are modified by introducing functional genes into their genome or by disrupting the wrong genes
- Takes place in *early embryonic development
When was research on use of CRISPR-Cas in germinal genetic genetic modification published?
- From 2015 onwards
- only 12 so far all from 2015-2019
- 2015 x1, 2016 x2, 2017 x5, 2018 x3, 2019 x3
*What are DNA repair mechanisms?
- Non-homologous end- joining (NHEJ)
- Homology- directed repair (HDR)
What are the risks of germinal gene editing?
- Off-target effects: modifications that occur in another area (uncontrolled)
- Repair by NHEJ route: random insertions or deletions (mutations on target, low efficiency HDR route)
- Mosaicism:
*Quotes on risks (from 2015 research paper)
- “Because the gene edited embryos are genetically mosaic, it would be impossible to predict gene editing outcomes through pre-implantation genetic diagnosis (PGD)”
- the pressing need to further improve the fidelity and specificity”
- “computational prediction based on sequence similarity to target sites failed to predict many off-target mutations”
- “not a current option due to both ethical and technical issues”
- “specificity of base editors needs more comprehensive investigation”
*What were the 3 research papers on CRISPR-Cas use in human embryos from 2020 on?
- *Frequent loss-of-heterozygosity in CRISPR-Cas-9-edited early human embryos
- *Allele-Specific Chromosomal Removal after Cas9 cleavage in human embryos
- *Frequent gene conversion in human embryos induced by double strand breaks
*How many human embryos were destroyed in 10 papers being published?
At least 866 human embryos destroyed (probably more)
*What are the ethical issues of genetic modifications on human embryos?
- Informed consent: inability of embryo to give it, will affect all its offspring, will be subject of research
- Therapy or reproductive option?: treatment foreseen before the conception of “patient”, questions about allocation of public resources
- Lead to less inclusive society + discrimination?: Private exploitation of techniques can lead to higher + lower genetic levels. “Genetic imperfection” would be choice of “irresponsible” parents (alr. happening in Spain e.g Down’s Syndrome)
- Ethical to produce “designer” children?: Germline gene editing opens door to human genetic improvement (case of children/ twins from China)
- Association with IVF
*In which cases is there no alternative for parents?
- 4-8 x 10^-8% of couples could benefit from gene editing of a certain gene
- cases of severe monogenic diseases in which all children would inherit the genotype of the disease
What is an autosomal dominant disease?
If one parent carries 2 disease-causing alleles (homozygous affected), all children will inherit the disease-causing genotype
What is an autosomal recessive disease?
If both parents carry 2 disease-causing alleles in the same gene (homozygous affected), all all children will inherit the disease-causing genotype
What are X-linked recessive diseases?
If the expectant mother carries 2 disease-causing alleles (homozygous affected) + father carries 1 disease-causing allele on his only X chromosome (hemizygous affected), all offspring would be affected
What was the Jiankui case?
- 2 twin girls born in 2018, whose DNA was modified with CRISPR/Cas to give them “protect” them against HIV
- Research has not been published
- Scientists agree it was irresponsible
What were the Jiankui case specifications?
- Falsified ethical approval documents
- Unfavourable benefit risk balance:
- chose target disease that can be prevented + treated
- Chose CCR5 gene which has important functions (still not fully known
- Experiment not considered therapeutic, it’s “improvement” - Embryonic destruction
*What is the current position of the scientific community?
- *Declared that in the future the clinical application of germline genetic edditing could become a realistic option
- *Door is not closed to a possible future use of germline gene therapy, but it is pointed out that today the unresolved issues make it innapropriate in embryos for later implantation
- *Requested continuation of research on embryos but failure to carry out any reproductive application
*What is the trend seen in scientists from Europe?
- *In March 2016 representative from more than 20 European countries came together to reflect on + promote responsible research with CRISPR-Cas. In July 2017, the consensus document was published which reflected this vision
- *Recommends conducting careful scientific research to built an evidence base
