Gene Editing Made Easy with CRISPR
"I don't believe medical discoveries are doing much to advance human life. As fast as we create ways to extend it we are inventing ways to shorten it." - Christiaan Barnard
CRISPR has turned out to be one of the biggest advances of 2015, with a lot of excitement surrounding this gene editing tool.
This path breaking discovery of the CRISPR-Cas 9 system led to scientist Jennifer Doudna receiving the 2015 breakthrough award for life sciences, awarded by a group of technology giants including Mark Zuckerberg. It was in 2012 that CRISPR was first shown to work as a genome engineering/editing tool and it has taken the last three years to show its versatility and put it to use in clinical situations.
CRISPR is a gene editing tool that lets scientists edit genomes with precision. The molecules discovered and crafted by Doudna and colleagues, can get into microbes and can make changes to the DNA at specific locations.
A Scientific Stampede:
There has been so much of buzz surrounding CRISPR and its vast possibilities that a lot of scientists are simultaneously working to use CRISPR for both medicinal as well as for agricultural purposes.
Teams of scientists from Harvard University and Broad University are coming out with successful stories about the benefits and uses of CRISPR, creating a stampede for this wonder discovery.
Researchers found that bacterial DNA has a sequence of repeating genes. Between these genes are interspersed some viral genes. This sequence is called “clustered regularly interspaced short palindromic repeats”, CRISPR for short.
How did viral genes come between bacterial genes? Researchers believe that this was possible with the help of an enzyme produced by a gene sequence called Cas (CRISPR-associated genes), which is located close to the CRISPR sequence.
When a virus attacks the bacterium, the Cas enzyme makes a precise cut in a particular fragment of the genome of the bacteria with repeat sequences, and places the gene of the virus in between. This is a sort of protective mechanism for the bacteria. If exposed to the same virus again, the bacterial cell recognizes it based on the viral DNA, and launches a mechanism to get rid of it. The Cas enzyme places a part in this mechanism as well.
The CRISPR/Cas system has got several implications in the medical field. Prior to its discovery, changes in the genome could be made, but they could not be guaranteed to take place precisely at the point that was required. This could result in dangerous consequences. Jennifer Doudna and Emmanuelle Charpentier found that with the help of a guiding RNA protein, the Cas9 enzyme could be directed to a particular part of the DNA and cut it with precision at a particular point, thereby allowing for modifications in the genome. They also used two Cas9 enzymes to produce two snips so that a part of the genome could be removed and replaced by another part.
The CRISPR/Cas 9system has revolutionized medical diagnosis and the following are some of the studies related to the uses of CRISPR technology
A) Sarcomas - Sarcomas are one of the most serious types of cancer. They are caused due to -
- Mutation in genes
- Over expression or activation of genes
Scientists Liu T and colleagues believe that CRISPR can be used to treat sarcomas due to their genetic basis using for gene editing function as well as epigenome silencing.
B) Cure for Genetic Disease of the Eye: Retinitis pigmentosa is a genetic disease of the eye that leads to blindness and has no cure. However, scientists now have successfully shown that CRISPR can be used to treat the genetic mutation in Retinitis pigmentosa patients.
C) Virus Resistant Cucumber: It is not only humans, but plants too that can benefit from CRISPR technology. Chandrashekaran A and colleagues have detailed the use of CRISPR in plant gene editing by developing virus resistant varieties of cucumber using this technology.
D) Inhibition of HIV1- Replication: HIV infection and subsequent development of AIDS has been one of the most menacing infections this turn of the century. CRISPR was used by Wang G and colleagues to inhibit the growth of HIV-1. However, the virus was also equipped with additional mechanisms to escape the inhibition. Further studies will be needed to see how the CRISPR-Cas mechanism could be useful in HIV infection.
E) Kidney Organoids Grown in the Lab: Gene editing tools and stem cell technology were used to grow organoids in the lab which could prove useful in the case of kidney disease.
F) Duchenne Muscular Dystrophy: The progression of Duchenne muscular dystrophy in mice was stopped by a team of scientists from Southwestern Medical Center using CRISPR-Cas 9 technology.
H) Designer Babies: The discovery of CRISPR has allowed for mutations in embryos which can lead to what is called ‘designer babies’. This is the most controversial implication of this new technology. Scientists can now possibly cut the DNA of embryos at a particular point with precision, and insert a new gene. Though there is a lot of research to be done and it is only in the experimental stage, there is a lot of attention being focused on this aspect.
Advances with CRISPR: Recently, 2 monkeys were born with mutations induced by the CRISPR/Cas9 system. Xingxu Huang and colleagues from the Nanjing University in China inserted mutations into the monkeys using this editing technology. Scientists so far have only been able to alter genes in mice and rats and this is the first case of primates born with mutations.
- Breakthrough DNA Editor Born of Bacteria - (https://www.quantamagazine.org/20150206-crispr-dna-editor-bacteria/)
- Nejat N, Rookes J, Mantri NL, Cahill DM “Plant-pathogen interactions: toward development of next-generation disease-resistant plants.”Crit Rev Biotechnol. 2016 Jan 22:1-9
- Wang G, Zhao N, Berkhout B, Das AT "CRISPR-Cas9 can inhibit HIV-1 replication but NHEJ repair facilitates virus escape" Mol Ther. 2016 Jan 22.
- Liu T, Shen JK, Li Z, Choy E, Hornicek FJ, Duan Z. "Development and potential applications of CRISPR-cas9 genome editing technology in sarcoma." Cancer Lett. 2016 Jan 21.
- Chandrasekaran J, Brumin M, Wolf D, Leibman D, Klap C, Pearlsman M, Sherman A, Arazi T, Gal-On A. "Development of broad virus resistance in non-transgenic cucumber using CRISPR/Cas9 technology." Mol Plant Pathol. 2016 Jan 25
- Helen Shen "First monkeys with customized mutations born" Nature doi:10.1038/nature.2014.14611
Latest Publications and Research on CRISPR
- Drosophila Xrcc2 regulates DNA double-strand repair in somatic cells. - Published by PubMed
- EMT signaling: potential contribution of CRISPR/Cas gene editing. - Published by PubMed
- Domain-specific introduction to machine learning terminology, pitfalls and opportunities in CRISPR-based gene editing. - Published by PubMed
- A genetic toolbox for metabolic engineering of Issatchenkia orientalis. - Published by PubMed
- CRISPR/Cas9 directed editing of lycopene epsilon-cyclase modulates metabolic flux for ß-carotene biosynthesis in banana fruit. - Published by PubMed