Genome Editing: Removal of Defective Gene

Image via ProstateCancerNewsToday

Most of the human body physical and biological expressions are attributed to the ‘Genes’- the carrier of our hereditary traits/characteristics.

When we state expressions, this includes both positive and negative traits. Positive traits are well recognised - a beautiful daughter from a beautiful couple, an inherent resistance of a child to diseases due to a robust immune system inherited from parents, hair colours, iris colour and many other.

What about the negative expressions - sickle celled anaemia, cystic fibrosis, haemophilia to name a few. These negative traits can be passed on from one of the parents and can also happen due to spontaneous mutation.

For a long time scientist have been trying to understand the cause of such negative genetic traits and how it can be cured. With advancement is the field of genetics, scientists are trying to develop gene therapy to address these issue and have come up with ‘Editing of Genomes’ for treatment of a disease.

Genome Editing

It is a very controversial topic. Human trying to play God through alteration the building blocks of life or a human being trying to ease the pain of his fellow human being suffering existence. This discussion can go on forever. But, yes, in spite of all the questions, scientist have developed ways for removing a defective gene from an individual and replacing it with a good gene to improve the quality of life, which is the birth right of every living individual.

How Genome Editing is done

For this we have to understand ‘Gene’. All must have heard about DNA (deoxyribonucleic acid) - the most popular used term being DNA testing or mapping to catch criminal in detective TV series/movies. In simple terms if we imagine ladder which has twists like a rope and coiled up tightly, we can picture the DNA structure. As a typical ladder, this DNA has many segments and each segment can be considered as a gene. When one of this segment (gene) is responsible for a negative characteristic, it expresses itself on an individual as a harmful condition such as sickle shape anaemia (Young, 2015). Now scientist have discovered methods for removing this bad segment of the DNA ladder and replacing it with a healthy segment so that the individual can lead a normal life.

Various methods such as Zinc finger nucleases (ZFNs), Transcription activator-like effector nucleases (TALENs) , have been proposed and test by scientist and one such recent discovery by scientist is ‘CRISPR’ in short for ‘Clustered Regularly Interspaced Short Palindromic Repeats’ (Park, et al 2016; Marc, et al 2017). 

CRISPR is actually a method used by bacteria for defence against virus attack and was discovered by accident in 1987 but has come a long way through development and refinement to be used for editing the genome.

Image via Cambridge

Sources

Marc A.J. Morgan et al. A cryptic Tudor domain links BRWD2/PHIP to COMPASS-mediated histone H3K4 methylation, Genes & Development (2017). DOI: 10.1101/gad.305201.117

Park, K.-E.; Park, C.-H.; Powell, A.; Martin, J.; Donovan, D.M.; Telugu, B.P.  Targeted Gene Knockin in Porcine Somatic Cells Using CRISPR/Cas Ribonucleoproteins. Int. J. Mol. Sci. 2016, 17, 810.

Young, S.A.M.; Miyata, H.; Satouh, Y.; Kato, H.; Nozawa, K.; Isotani, A.; Aitken, R.J.; Baker, M.A.; Ikawa, M. CRISPR/Cas9-Mediated Rapid Generation of Multiple Mouse Lines Identified Ccdc63 as Essential for Spermiogenesis. Int. J. Mol. Sci. 2015, 16, 24732-24750.

Further Readings

Braverman, I. (edt. 2017) Gene Editing, Law, and the Environment: Life Beyond the Human.  Routledge; 1 edition

Doudna, J. A., and Sternberg, S. H.  (2017) A Crack in Creation: Gene Editing and the Unthinkable Power to Control Evolution. Houghton Mifflin Harcourt

Qiao, W. (2016) The Dynamic Principle Of Gene Editing. Cambridge University Press; 1 edition