Here we review three foundational technologies—clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9), transcription activator-like effector nucleases (TALENs), and zinc-finger nucleases (ZFNs).
In gene editing, a mutated gene is revised, removed, or replaced at the DNA level. In gene therapy, the effect of a mutation is offset by inserting a “healthy” version of the gene, and the disease-related genes remain in the genome.
Human genetic modification is the direct manipulation of the genome using molecular engineering techniques. Recently developed techniques for modifying genes are often called “gene editing.” Genetic modification can be applied in two very different ways: somatic genetic modification and germline genetic modification.
Older gene-editing tools use proteins instead of RNA to target damaged genes. But it can take months to design a single, customized protein at a cost of more than $1,000. With CRISPR, scientists can create a short RNA template in just a few days using free software and a DNA starter kit that costs $65 plus shipping.
Genome editing is a way of making changes to specific parts of a genome. Scientists have been able to alter DNA since the 1970s, but in recent years, they have developed faster, cheaper, and more precise methods to add, remove, or change genes in living organisms.
Gene editing techniques have benefits such as: the treatment of diseases; creation of model organisms for basic biomedical research; development of transgenic foods, among other applications.
Specific nucleases (SNs), including ZFNs, TALENs, and CRISPR (clustered regularly interspaced palindromic repeats), are powerful tools for genome editing (GE). These tools have achieved efficient gene repair and gene disruption of human primary cells.
Each chromosome contains hundreds to thousands of genes, which carry the instructions for making proteins. Each of the estimated 30,000 genes in the human genome makes an average of three proteins.
Scientists have also used CRISPR to detect specific targets, such as DNA from cancer-causing viruses and RNA from cancer cells. Most recently, CRISPR has been put to use as an experimental test to detect the novel coronavirus.
Scientists are studying CRISPR for many conditions, including high cholesterol, HIV, and Huntington's disease. Researchers have also used CRISPR to cure muscular dystrophy in mice. Most likely, the first disease CRISPR helps cure will be caused by just one flaw in a single gene, like sickle cell disease.
CRISPR technology is a simple yet powerful tool for editing genomes. It allows researchers to easily alter DNA sequences and modify gene function. Its many potential applications include correcting genetic defects, treating and preventing the spread of diseases and improving crops.
First CRISPR Law: Selling “Gene-therapy Kits” Will Be Illegal in California Unless They Carry a Warning. Following unanimous support in the Legislature, the Governor Gavin Newsom signed the first bill into law addressing the emerging CRISPR technology.
The CRISPR sequence is transcribed and processed to generate short CRISPR RNA molecules. The CRISPR RNA associates with and guides bacterial molecular machinery to a matching target sequence in the invading virus. The molecular machinery cuts up and destroys the invading viral genome.
In the DNA delivery format, the CRISPR DNA vector enters the cell and translocates to the nucleus, where the Cas9 mRNA and gRNA are transcribed. In the RNA delivery format, the Cas9 mRNA and gRNA are cotransfected into the cell cytoplasm, where the mRNA is translated to produce functional Cas9 protein.
We now demonstrate that CRISPR/Cas9 mutagenesis in zebrafish is highly efficient, reaching up to 86.0%, and is heritable. The efficiency of the CRISPR/Cas9 system further facilitated the targeted knock-in of a protein tag provided by a donor oligonucleotide with knock-in efficiencies of 3.5-15.6%.
Researchers in the U.S. have begun editing the genes of adults with devastating diseases, using a tool known as CRISPR. China has already launched multiple trials of CRISPR in humans.
25, 2019.
- Cellectis. Cellectis focuses on using TALEN gene editing to develop allogeneic chimeric antigen receptor T-cell (CAR-T) therapies.
- CRISPR Therapeutics. As you probably gathered from its name, CRISPR Therapeutics uses the CRISPR gene-editing method.
- Editas Medicine.
- Intellia Therapeutics.
- Sangamo Therapeutics.
CRISPR genome editing may result in unwanted heritable genetic changes, which could lead to long-term risks in a clinical context. Three independent studies published on the preprint platform bioRxiv have reported unintended DNA changes adjacent to the target site when using CRISPR/Cas9 in human embryos.
Disadvantages of CRISPR technology: CRISPR-Cas9 off-target:The effect of off-target can alter the function of a gene and may result in genomic instability, hindering it prospective and application in clinical procedure.
Genomic research that serves to identify pre-existing conditions can potentially deprive patients from health insurance and medical care. Moreover, there can be unintended health consequences of genetically modified crop produc- tion, including increased risks of contamination and loss of biodiversity.
A lab experiment aimed at fixing defective DNA in human embryos shows what can go wrong with this type of gene editing and why leading scientists say it's too unsafe to try. In more than half of the cases, the editing caused unintended changes, such as loss of an entire chromosome or big chunks of it.
In a mouse model of liver regeneration, the companies' scientists demonstrated that unlike conventional gene therapy, CRISPR/Cas9 can facilitate the insertion of gene constructs that remain active inside liver cells, even as they divide and expand in order to restore the tissue that was lost.
CRISPR/Cas is an extremely powerful tool, but it has important
limitations.
It is:
- difficult to deliver the CRISPR/Cas material to mature cells in large numbers, which remains a problem for many clinical applications.
- not 100% efficient, so even the cells that take in CRISPR/Cas may not have genome editing activity.
- CRISPR Could Correct The Genetic Errors That Cause Disease.
- CRISPR Can Eliminate the Microbes That Cause Disease.
- CRISPR Could Resurrect Species.
- CRISPR Could Create New, Healthier Foods.
- CRISPR Could Eradicate The Planet's Most Dangerous Pest.
When the target DNA is found, Cas9 – one of the enzymes produced by the CRISPR system – binds to the DNA and cuts it, shutting the targeted gene off. Using modified versions of Cas9, researchers can activate gene expression instead of cutting the DNA. These techniques allow researchers to study the gene's function.
The changes are the result of DNA-repair processes harnessed by genome-editing tools. CRISPR–Cas9 uses a small strand of RNA to direct the Cas9 enzyme to a site in the genome with a similar sequence. The enzyme then cuts both strands of DNA at that site, and the cell's repair systems heal the gap.
In short, CRISPR/Cas9 is a molecular tool, which can be used for 'gene therapy'. CRISPR/Cas9 is able to deliver a correct gene into human genome to fix a defect gene.
Transcription activator-like effector nucleases (TALEN) are restriction enzymes that can be engineered to cut specific sequences of DNA. The restriction enzymes can be introduced into cells, for use in gene editing or for genome editing in situ, a technique known as genome editing with engineered nucleases.
