CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea.
Cas9 (CRISPR-associated protein 9) is an enzyme that uses CRISPR sequences as a guide for recognizing cleave specific strands of DNA that are complementary to the CRISPR sequence. CRISPR is found in approximately 50% of sequenced bacterial genomes and nearly 90% of sequenced archaea.
The first description of CRISPR is from Osaka University researcher Yoshizumi Ishino and his colleagues in 1987. They accidentally cloned part of CRISPR sequence together with the 'iap' gene (Isozyme conversion of Alkaline Phosphatase) that was their target. Repeats were observed in the archaeal organism of Haloferax and Haloarcula.
In 2001, Mojica and Ruud Jansen, who were searching for additional interrupted repeats, proposed the acronym CRISPR to alleviate the confusion stemming from numerous acronyms used to describe the scientific literature.
In 2005, three independent research groups showed that some CRISPR spacers are derived from phage DNA and extrachromosomal DNA such as plasmids.
The first publication proposing a role of CRISPR-Cas in microbial immunity, by the researchers at the University of Alicante, predicted a role for the RNA transcript of spacers that could be analogous to the RNA interference system used by eukaryotic cells. The CRISPR array is made up of an AT-rich leader sequence followed by repetition that is separated by unique spacers.
The stages of CRISPR immunity for each of the three major types of adaptive immunity: (1) acquisition ; (2) crRNA processing ; (3) interference.
The cas genes in the adaptor and effector modules of the CRISPR-Cas system are believed to have evolved from two different ancestral modules. CRISPR can immunize bacteria against certain phages and thus halt transmission. CRISPR technology has been applied in the food and farming industries to engineer probiotic cultures and to immunize industrial cultures.
In July 2019, CRISPR was used to experimentally treat a patient with genetic disorder. The patient was a 34-year old woman with sickle cell disease. In March 2020, CRISPR modified virus was injected into a patient's eyes in an attempt to treat Leber congenital amaurosis. In the future, CRISPR gene editing could potentially be used to create new species or revive extinct species from closely related ones.
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