An overview of the groundbreaking gene-editing tech
The ability to edit the human genome is a cause of much fanfare and hype. While the idea of gene-editing isn’t new, there was a need for an efficient and easy way to manipulate genes in the scientific community. In order to better understand how our genes work, researchers required a method of manipulating them.
This is the reason for the CRISPR-Cas9 system taking off now. The recent technological breakthrough was a result of a collaboration between Jennifer Doudna (a Howard Hughes Medical Institute Investigator and professor of molecular and cell biology and chemistry at the University of California, Berkeley) and Emmanuelle Charpentier (director of the new Max Planck Institute of Infection Biology) in 2012.
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats (pronounced as crisper) and it is based on a natural system used by bacteria to protect themselves from viral infections. When bacteria detects the presence of viral DNA, it produces guide RNA (gRNA). It is made of 2 types of RNA, one of which matches the sequence of the invading viral DNA that is intended to be cut.
The gRNA forms a complex with a protein called Cas9. It is a nuclease, a type of enzyme that is capable of cleaving the phosphodiester bonds between the nucleotide subunits of nucleic acids.
Researchers now have the tools to cut their target sequence at precise locations on the genome by changing the gRNAs to match the target. This can be done not only in a test tube, but also in living cells.
In living cells, the gRNA-Cas9 complex will lock onto a short sequence on the DNA. This is the protospacer adjacent motif (PAM) sequence, a DNA sequence immediately following the DNA sequence targeted by the Cas9 nuclease.
The Cas9 nuclease will then unwind the DNA, match it to its target RNA, and positions itself so two active sites can cut the double-stranded DNA at a precise, targeted sequence.
The cell then tries to repair the cut but this process is error-prone leading to random mutations, resulting in the gene being disabled.
The removal of certain sequences then allows scientists to study the function of the gene. Scientists can also harness this technology to make double strand breaks where we might like to introduce a small change in the genome.
Our genes help shape who we are individually and as a species. Every cell in our body contains a copy of our genome. With more than 20000 genes in our genome together with more than 3 billion base pairs, there is still much to be discovered about our DNA.
Genes also have a large influence on our health and with improvements in genetic sequencing, researchers have been able to indentify genes that affect our risk of disease. Using this information, we can hopefully continue to diagnose, treat, and manage conditions that affect many around the world.
Stay tuned and check out part 2 of this mini-series, where the current and future uses of the CRISPR-Cas9 system and the challenges we face in implementing it will be discussed.