CRISPR, short for “clustered regularly interspaced short palindromic repeats,” is a tool that allows scientists to manipulate specific parts of a genome. Although first discovered in 1993 in archaea immune systems, the CRISPR gene editing technique is also naturally used by bacteria to defend against pathogens. Both archaea and bacteria are prokaryotes: simple, single-celled organisms that lack the complex cellular compartmentalization and DNA organization found in eukaryotic cells. Eukaryotes, such as plants and animals, do not naturally have a CRISPR system.
Cas9 is a CRISPR enzyme that cuts double-stranded DNA for the removal, addition, or substitution of a particular DNA sequence. It is led to its target location by guide RNA (gRNA) that binds to a precise section of the DNA strand based on its complementary base pairs.
In April 2003, researchers announced that they had thus successfully completed the Human Genome Project. With the exact order of base pairs on each chromosome determined, scientists began to map out the functional elements of the genome (primarily genes). Researchers around the world have since contributed their findings to the Encyclopedia of DNA Elements (ENCODE), a public database that has been instrumental in determining the functions and roles of particular genes.
As a result of these continued efforts, we better understand the relationship between genetics and disease. Individuals may be more or less susceptible to certain disorders depending on their particular version or mutation of a gene. For example, BRCA1 and BRCA2 genes normally produce tumor-suppressing proteins, so individuals with inactivating mutations have a higher risk of breast or ovarian cancer.
Now that CRISPR-Cas9 technology has been adapted to work in human cells, it has immense potential to someday provide in vivo gene therapy by editing problematic DNA sequences.