DNA is inserted, replaced, or removed from a genome using artificially engineered nucleases, or "molecular scissors". The nucleases make specific double-strand breaks (DSBs) at desired places in the genome. The cell’s own mechanisms repair the induced break(s) by natural processes.
To understand the function of a gene or a protein one interferes with it in a sequence-specific way, and watches its effects on the organism. However, in some organisms it is difficult or impossible to do site-specific mutation. Therefore more indirect methods have to be used. Examples are:
- Silencing the gene of interest by short RNA interference (siRNA). Yet gene disruption by siRNA can be variable and incomplete.
- Genome editing with nucleases such as ZFN. This is different from siRNA. The engineered nuclease (the enzyme which cuts the DNA) is able to modify DNA-binding. This way it can (in principle) cut any targeted position in the genome, and introduce change in sequences for genes which cannot be specifically targeted by conventional RNAi.
The CRISPR/Cas9 method[change | change source]
In 2017 this system was announced as one of the biggest scientific achievements of the year. Cas9 is an enzyme which, with a guide RNA, can put a new sequence of DNA into a genome. Sir John Skehel said "That might allow you to knock out a particular gene in a cell, or introduce a particular gene, or correct a particular mutated gene that you want to work better".
References[change | change source]
- sometimes "genome editing with engineered nucleases" (GEEN)
- Carey, Nessa 2019. Hacking the code of life: how gene editing will rewrite our futures. Icon books, London. ISBN 978-1-78578-625-9
- The four types are: zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), the CRISPR/Cas system, and re-engineered homing endonucleases.
- Esvelt, KM.; Wang, HH. (2013). "Genome-scale engineering for systems and synthetic biology". Mol Syst Biol. 9 (1): 641. doi:10.1038/msb.2012.66. PMC 3564264. PMID 23340847.
- Tan W.S.; et al. (2012). "Precision editing of large animal genomes". Adv Genet. 80: 37–97. doi:10.1016/B978-0-12-404742-6.00002-8. PMC 3683964. PMID 23084873.
- Puchta, H.; Fauser, F. (2013). "Gene targeting in plants: 25 years later". Int. J. Dev. Biol. 57: 629–637. doi:10.1387/ijdb.130194hp.
- Fire A. et al 1998. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature 391 (6669), 806-811 (1998).
- Method of the Year 2011. Nat Meth 9 (1), 1-1.
- Gallagher, James 2015. Dawn of gene-editing medicine? BBC News Health. 
- Gallagher, James 2016. Scientists get 'gene editing' go-ahead. BBC News Health. 
- a British virologist and emeritus scientist at the Francis Crick Institute in London.
- The biggest scientific developments of 2017, according to two scientists at the Royal Society of London.