Let us understand the natural immune system of the bacteria. These are infected by a virus and become bacteriophase. Small pieces of virus are captured by the bacteria and these are inserted into their own DNA. A pattern is formed called CRISPR arrays. It enables bacteria to remember viruses or closely related viruses.
When there is another attack, bacteria produce RNA segments from CRISPR arrays which recognise and attach to specific regions of the DNA of viruses.
Bacteria then use Cas9 or similar enzyme to cut DNA apart, thus disabling the virus.
In short, bacteria’s DNA gallery stores the genetic code of any virus that attracts it. The bacteria checks this gallery and when it finds a match, it activates a CRISPR-associated enzyne called Cas9 to cut it and disable it.
Editing Tool
CRISPR has become a highly precise gene editing tool. It is used to remove, add or alter section of the DNA sequence. It is a genetic manipulation tool.
The immune system, we have discussed, has been used to edit DNA.
How CRISPR Works
A small piece of RNA with short guide sequence is created. It attaches to specific target sequence in the DNA of the cell. The guide RNA attaches to CaS9 enzyme. When introduced into the cells, guide RNA recognises the intended DNA sequence. CaS9 enzyme cuts the DNA at targeted location. It snips the DNA. The cells then repair the broken DNA. Scientists can insert replacement DNA into the cell to stitch the broken cells together. The existing segment has been replaced by a customised DNA sequence. The genetic material can take additions or deletions or alterations.
Thus this is a mirror work of bacteria’s immune system. Bacteria have a natural editing system to have an immune defence. It has been adapted to develop CRISPR.
Genome editing is a group of technologies that give scientists an ability to change an organism’s DNA.
CRISPR is faster, more accurate, more efficient approach to genome editing.
Uses
CRISPR is used to prevent and treat diseases. It is more useful in single cell diseases, and promises to be useful in complex diseases.
Genome editing is limited to stomatic cells, and is isolated to certain tissues. It could be used to edit early embryos or germline cells or eggs and sperms. However, this affects progeny. It is a moot point whether it could be used to produce designer babies, say more intelligent and beautiful. It is illegal in the US and elsewhere. CRISPR can be used to produce mice where 80 per cent, or 100 per cent are females. Mosquitos can be made to produce male mosquitos and thus the disease producing, female mosquitos could be avoided.
How Used
CRISPR injection is administered into the eye directly. It consists of a non-pathogenic virus called AAV carrying CaS9 protein and its guide RNA.
Virus are used in gene therapy and editing as they have the ability to get into the cells.
History of CRISPR-CaS9
Crispr-CaS brings find and replace function in text files to the complex task of altering DNA.
It was launched in August 2012. US scientist Jennifer with her European collaborator Emmanuelle published a paper on CRISPR-CaS9. In January 2013 MIT and Harvard researchers adapted CRISPR-CaS9 to edit genes in mice and human cells. In August 2013, CRISPR was used to engineer plant genomes. In March 2015, scientists in the US and China explore CRISPR on stem cells to engineer human organs from genetically altered pigs. In February 2016, the UK allows scientists to alter human embryos using CRISPR. In June 2016, the US allows CRISPR to alter T cells for treating cancer patients. In May 2017, CRISPR is used by the US and Chinese scientists for HIV treatment. It was also shown that cardiac ailment can be treated using CISPR. In March 2018, genie editing of two human embryos was done by a Chinese scientist to disable a genie that allows HIV to enter the cells. In March 2020, for childhood blindness, a patient was treated using CRISPR to alter photoreceptor genes in the US. In September 2020, a Covid test was created using CRISPR called Feluda. In October 2020, Jennifer and Emmanuelle hot a Nobel for their work on CRISPR. In October 2021, there are trials of CRISPR-based cancer treatment.