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What is CRISPR?
- CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats.
- CRISPR - Cas9 is the most prominent genome editing technique .
- It allows researchers to permanently modify genes in living cells and organisms.
- This can be used to correct mutations at precise locations in the human genome to treat genetic causes of diseases.
- Correcting the mutation in an embryo ensures that the child is born healthy and the defective gene is not passed on to future generations.
How does it work?
- The gene editing tool has two components :
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- a single-guide RNA (sgRNA) that contains a sequence that can bind to DNA.
- the Cas9 enzyme which acts as a molecular scissor that can cleave DNA.
- In order to selectively edit a desired sequence in DNA, the sgRNA is designed to find and bind to the target.
- The genetic sequence of the sgRNA matches the target sequence of the DNA that has to be edited.
- Upon finding its target, the Cas9 enzyme swings into an active form that cuts both strands of the target DNA.
- One of the two main DNA-repair pathways in the cell then gets activated to repair the double-stranded breaks.
- While one of the repair mechanisms result in changes to the DNA sequence, the other is more suitable for introducing specific sequences to enable tailored repair.
- In theory, the guide RNA will only bind to the target sequence and no other regions of the genome.
- But the CRISPR-Cas9 system can also recognise and cleave different regions of the genome than the one that was intended to be edited.
- These “off-target” changes are very likely to take place when the gene-editing tool binds to DNA sequences that are very similar to the target one.
- Though many studies have only found few unwanted changes suggesting that the tool is probably safe, researchers are working on safer alternatives.
Why is CRISPR- Cas9 system significant?
- Normally, if sperm from a father with one mutant copy of the gene is fertilized in vitro with normal eggs, 50% of the embryos would inherit the condition.
- However, when the gene-editing tool was used, the probability of inheriting the healthy gene increased from 50 to 72.4%. There was also no off-target snipping of the DNA.
- The edited embryos developed similarly to the control embryos indicating that editing does not block development.
- Clinical trials are under way in many countries to use this tool for treating cancer.
- It was shown in mice that it is possible to shut down HIV-1 replication and even eliminate the virus from infected cells.
- In agriculture, a new breed of crops that are gene-edited will become commercially available in a few years.
- Given all these, making gene editing possible in human reproductive cells deserves serious considerations in terms of legal, social and ethical consequences.
Source: The Hindu
