What is CRISPR-Cas9?
How Women Are Undervalued
I have always thought that women are wonderful creatures. It is my fervent belief that if World history had included far more women in leadership roles the planet might be not be in the mess (to put it politely) that it is. In chemical terms, I think it can be argued that testosterone has done as much global damage as carbon dioxide.
Nobel Prizes are among the most prestigious awards for achievement in various fields, and I think it is a shameful fact that as of this year only 57 women have been awarded Nobel Prizes compared to over 866 men! With all of the above in mind, I was delighted to read that the 2020 Nobel Prize for Chemistry had been awarded to Dr Jennifer Doudna from the USA and Dr Emmanuelle Charpentier from France. Doudna and Charpentier were given the prize for their development of the gene-editing tool known as CRISPR-Cas9, or often simply “CRISPR”.
What is CRISPR-Cas9?
CRISPR stands for “clustered regularly interspaced short palindromic repeats”. It is a family of DNA sequences found in the genetic material of unicellular organisms, including bacteria. The sequences are derived from DNA fragments of viruses called bacteriophages that have previously infected the organism, and they are used to detect and destroy the DNA of similar viruses in a subsequent attack. Cas9 is one of a group of enzymes (and other proteins) that uses CRISPR sequences as a guide to recognise and break strands of DNA that are complimentary to the CRISPR sequence. Hence, CRISPR and Cas9 constitute a primitive immune system. The information from the CRISPR sequences is communicated to Cas9 via small RNA molecules. Doudna and Charpentier recognised that the system could be modified to produce a tool that would allow extremely precise editing of DNA in essentially any organism directed by modified RNA molecules they synthesised called guide RNAs. Since their original publications in 2012, CRISPR-Cas9 has been widely recognised as the biggest breakthrough in the biological sciences since the discovery of DNA.
The History of Gene Editing
For a long time geneticists used chemicals or radiation to cause mutations, but they had no way of controlling where in the genome the mutation would occur. For several years now researchers have been using “gene targeting” to introduce changes in specific places in the genome, by adding or removing either whole genes or single bases. Traditional gene targeting has been very valuable for studying genes and genetics, however it takes a long time to create a mutation, and it is fairly expensive. Several gene editing technologies have more recently been developed to improve gene targeting methods. Before 2015 these “engineered nucleases” were of 3 main types: zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and engineered meganucleases. CRISPR-Cas9 was added to the list in 2015, and use of the technique has mushroomed since then.
Of the four methods mentioned above, meganucleases’ method of gene editing is the least efficient. ZFNs were developed to overcome the limitations of meganucleases, but both methods are relatively unpredictable. Because of this, their use requires high degrees of expertise and prolonged, costly validation processes. TALENs are the most precise and specific method, but development of new ones requires significant expertise in molecular biology and protein engineering. CRISPR is slightly less precise, but it is the quickest, cheapest method, and it requires the least expertise in molecular biology. As Doudna states in her book “A Crack In Creation: The New Power to Control Evolution”, “CRISPR finally made gene editing available to all scientists. Previous tools—primarily ZFNs and TALENs—were difficult to design and prohibitively expensive. For this reason, many labs, including my own, were unwilling to take on the challenges of research using gene editing. With CRISPR, however, scientists can easily design a version to target their gene or genes of interest, prepare the requisite Cas9 protein and guide RNA, and execute the experiments themselves using standard techniques, all within mere days and without requiring any outside assistance.”.
CRISPR Rewards and Risks
CRISPR-Cas9 has a number of potential uses in studying the function of genes, and editing them in both plant and animal cells.It could provide new treatments for many diseases, including genetic diseases and cancers. There have been concerns, however, that such a powerful tool might also have adverse effects, if not used carefully. I plan to discuss the potential rewards and risks in a future post.
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