Scientists use CRISPR gene-editing technology to enable specific genes to be modified, removed, or added.
Scientists have long sought the ability to alter the genes in living cells, and the development of a new technology called CRISPR has afforded researchers the opportunity to edit particular genes of interest. It is an acronym for clustered regularly interspaced short palindromic repeats (CRISPR), which is a group of bacterial DNA sequences that is used to defend against viruses. The system can be altered and used to target and modify specific gene sequences. It works with a protein called Cas9, which is a multipart endonuclease enzyme used to defend against viruses. It can be used to target and modify specific gene sequences. CRISPR works by guiding the Cas9 protein to a target gene and actively binding it with a piece of guiding RNA to form a structure called the Cas9-guiding RNA complex. This complex is then introduced into the cell. In the cell, the RNA binds to part of the target gene and the Cas9 protein cuts the DNA into pieces. From here, broken DNA strands get repaired in one of two ways: Either the target gene gets disabled, allowing its function to be studied, or the target gene gets replaced with a functional gene if a damaging mutation is present. This gene modification technique can permanently alter the genes of an organism and can be used to add or remove almost any DNA sequence within a genome.
Gene Editing Using CRISPR
The gene editing performed by CRISPR has many broad-reaching applications. In the field of medicine, this technique is currently being used to research a wide variety of diseases and disorders, including sickle cell disease, hemophilia, and cystic fibrosis. Each of these is of interest because they are caused by mutations in single genes. In 2017, CRISPR was successfully used to remove HIV from a living organism. This eliminated all symptoms of the disease in the patient. In 2018, Chinese men and women took part in an experiment to remove HIV infection starting at the embryonic level. The goal was to inactivate the gene for a cell surface protein called CCR5 that HIV must bind to in order to enter and infect cells. Scientists took the sperm of HIV infected men, washed the sperm, thereby removing any HIV present, and injected the sperm into an egg. CRISPR gene editing material was also injected into the resultant embryo. One pregnancy was achieved and produced twins; one of those twins was found to have both copies of CCR5 disabled. This means that this twin should be able to resist HIV infection.
CRISPR was also used to target the control center of cancer cells, essentially shutting down their replication. CRISPR has also been used to force bacterial strains known as "superbugs" to attack themselves, including methicillin-resistant Staphylococcus aureus (MRSA). Scientists did this by inserting antimicrobial genes into the bacteria, causing them to self-destruct. In the future, CRISPR may also make it possible to correct mutations at their specific locations within the genome and, thus, treat genetic causes of disorders in both plant and animal species. CRISPR is new technology, and as such, may have many more applications that have yet to be investigated and proved medically valuable.
As with any DNA technology, however, ethical concerns involving direct human genetic modification are always present.
Most of the gene edits performed using CRISPR are made to somatic (body) cells, and are therefore not inherited by offspring during sexual reproduction. The best-known experimental uses of CRISPR to edit genes in body cells have been used in researching inherited conditions caused by a single mutant gene, such as sickle cell disease, Tay-Sachs disease, or Huntington's disease. Bioethical considerations of using CRISPR include whether the technique could be used to increase human intelligence or make someone taller or shorter. Using CRISPR to modify a person's genome presents the dilemma of "custom designing" an offspring, so there have been several calls by governments and international organizations, such as UNESCO, to ban the use of CRISPR on human gametes.