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Crispr Cas 9
CRISPR was first discovered as bacterial immune system which defends against viruses. It was discovered by Francisco Mojica, a scientist at the Univerisy of Alicante in Spain. The CRISPR serves as a genetic memory to help the cell to detect and fight the invaders. The theory was first experimentally demonstrated in 2007. In January 2013, the Zhang lab successfully invented a mechanism to engineer CRISPR to modify genome sequence in mice and human cells.
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. It is the basis of CRISPR-Cas9 gene editing technology that is designed to target specific sequences of of genetic code and edit DNA for desired purposes. The CRISPR technology is used to modify genes in living organisms and cure genetic mutations in human genome[1].
The CRISPR-Cas9 consists of two major molecules that mutates the target DNA:
- An enzyme called Cas9, which act as a molecular scissor that can cut two strands of DNA at specific location and lets desired bits of DNA to be added or removed.
- Guide RNA(gRNA) is a small piece of pre-set RNA sequence located in a longer RNA scaffold. The scaffold binds to DNA and the pre-set sequence leads Cas9 to the desired location of genome. It is a tool to make sure Cas9 cuts at right location.
The gRNA is designed to find and attach to specific sequence in DNA because the gRNA has bases that are complementary to target DNA sequence in genome. Cas9 follows gRNA to the same location in DNA and cuts the two strands of DNA. The cell recognizes the damage in DNA and tries to repair it. The DNA repair mechanism is used to make changes in genes as desired[2].
Ethical issues are arising with the topic 'genetic engineering'. With technology like CRISPR-Cas9, the controversies are always variety. The changes in the genome sequence does not pass down to further generations unless somatic cells. Embryotic cell genetic engineering always faces ethical issues. Somatic cell gene editing is illegal in many countries currently[3].
Other genetic engneering mechanisms:
- S. Phygenes (spCas9)
- S. Aureus (scCas9)
- HiFi Cas 9
- Nickase Cas 9
- Nuclease Cas 9[4]
Reference