GENE EDITING








                                              

GENE EDITING: HOW DOES IT WORK? WHAT ARE ITS PROS AND CONS?


Genome editing, or genome engineering, or gene editing, is a type of genetic engineering in which DNA is inserted, deleted, modified or replaced in the genome of a living organism. Unlike early genetic engineering technique that randomly inserts genetic material into a host genome, genome editing targets the insertions to site specific locations.

Gene editing, the ability to make highly specific changes in the DNA sequence of a living organism, essentially customising its genetic makeup. Gene editing is performed using nucleases that have been engineered to target a specific DNA sequence, where they cut the DNA strands enabling removal of existing DNA and insertion of replacement DNA.



Gene editing is accomplished by four main gene editing techniques. Each technique has its own unique advantages and disadvantages. 

The earlier methods include :-
  • Restriction Enzymes: The Original Genome Editor



No one knew how to edit genes back in the mid twentieth century. It was a dream come true for scientists when restriction enzymes were discovered in the 1970s.Restriction enzymes recognize a particular DNA sequence and cut the DNA strand at
that particular sequence giving an opportunity to insert a new DNA material at the location.Restriction enzymes are not commonly used for gene editing these days since they are limited by the nucleotide sequence they recognize, but they still are widely used today for molecular cloning. 
  • Zinc Finger Nucleases (ZFNs): Increased Recognition Potential



As time went on, the need for precision in genome editing became more evident. A gene editing mechanism was needed that recognized the site they wanted to edit, as off target effects were extremely harmful. The discovery of zinc finger nucleases(ZFN) in the 1980s addressed this issue.ZFNs are composed of two parts: an engineered nuclease(Fokl ) fused to zinc finger DNA-binding domain recognizes a 3-base pair site on DNA and can be combined to recognize longer sequences. Additionally, the ZFNs function as dimers, increasing the length of the DNA recognition site and consequently increasing specificity.One main hurdle with using ZFNS was that 3-base pair requirement made the design more challenging. Guanine-rich target sites appeared to be more efficient at editing versus non guanine rich sites.
  • TALENs Gene Editing: Single Nucleotide Sequence



In the year 2011,a new gene editing technique came into being which was an improvement of the ZFN technique. Transcription Activator-Like Effector Nucleases(TALENs) are structurally similar to ZFNs. Both methods use the Fokl nuclease to cut DNA and require dimerization to function, however the DNA binding domain differ. TALENs use transcription activator like effectors(TALEs),tandem arrays of 33-35 amino acid repeats.Even with a single nucleotide resolution, using TALENs as a gene editing tool was still time and cost intensive and showed decreased editing efficiency in highly methylated regions.
The newest form of gene editing changed everything. In 2012 while scientists were still searching for an easier and faster way to edit genetic sequences, they discovered a new method derived from CRISPR-Cas9, a system that has long existed in bacteria to help them fight off invading viruses. The teams lead by Jennifer Doudna and Emmanuelle Charpentier rocked the science world with first biochemical description of CRISPR. In 2013,Feng Zhang described how CRISPR could be used to edit eukaryotic DNA. Since these discoveries, CRISPR as a gene editing tool has seen immense development.
CRISPR is a two- component system consisting of a guide RNA and a Cas9 nuclease. The Cas9 nuclease cuts the DNA within the -20 nucleotide region defined by the guide RNAs. Certain algorithms have been developed to reduce off-target mutations.
Even though gene editing has so many benefits, it has its own pros and cons.

PROS OF GENE EDITING

  1. Cancer therapeutics:- T cells modified using gene editing can locate and kill cancer cells.
  2. Drug Discovery :- Genetic makeup can potentially speed up the drug discovery process.
  3. Genetic Diseases:- Genetic diseases can be prevented from transmitted into the offsprings using gene editing.
  4. Pest Resistant Crops:- According to Jennifer Doudna, instead of using tons of insecticides and pesticides, by using CRISPR plants can be protected from insects and pests in a healthier way.

CONS OF GENE EDITING 

  1. Ethical issue:- Gene editing according to a lot is going against nature. Falling ill and dying prematurely is a natural happening.
  2. Safety:-Even a slight mistake in the process of gene editing can cost the life of any living being.
  3. Biodiversity:- If all human beings are genetically modified then natural biodiversity will be completely lost.
  4. Cost:-Even though CRISPR is said to be cost effective, gene editing is fairly expensive. What would happen if only the rich and elite could afford it and let the poor ones die?



GENOME EDITING IN CROPS




All over the world, scientists are discussing the opportunities and risks of genome editing. Plant geneticists want to breed resilient, high-yield plants to combat famine. Critics warn against the unpredictable impact on human health and the environment. Medical experts want to cure hereditary diseases and treat cancer while ethicists fear that this could lead to “designer humans”.

GENOME EDITING IN HUMANS



Medics hope that they will be able to cure monogenic hereditary diseases such as Huntington’s disease, muscular dystrophy and cystic fibrosis. Interventions into the immune system also make it possible to treat acquired diseases such as cancer and AIDS. But many ethical issues have not yet been resolved. What impact do the changes have on the interaction of the genes? And how can we prevent unwanted, “off-target” effects that may, for example, modify genes that were not supposed to be modified and could cause cancer?

CONCLUSION 



The pros and cons of genetic engineering give us an idea of results of genetic engineering. Thus, in many countries and laws have already been put forward to bring the best outcome. With proper laws and control over it's usage, it will definitely be a gift for humankind.








Suraj Nandi on behalf of SBE-VIT

Author & Editor

Hope you enjoyed the acticle, stay tuned for more such interesting articles and events from SBE-VIT!!

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