- You may have heard about CRISPR or CRISPR/Cas9, a powerful gene-editing tool that allows scientist to edit our DNA.
- But how did the CRISPR technology come about? CRISPR discovered in the span of several years and mostly by accident. Following is a chronological order of CRISPR discovery.
- 1 1. Identification of Repeated DNA sequences
- 2 2. Discovery of the Similar Repeats
- 3 3. Discovery of CRISPR and its function
- 4 4. Discovery of Cas9 and PAM
- 5 5. Hypothetical scheme of adaptive immunity
- 6 6. Experimental demonstration of adaptive immunity
- 7 7. Spacer sequences are transcribed into guide RNAs
- 8 8. CRISPR acts on DNA targets
- 9 9. Cas9 cleaves target DNA
- 10 10. Discovery of tracrRNA for Cas9 system
- 11 11. Biochemical characterization of Cas9-mediated cleavage
- 12 12. CRISPR-Cas9 harnessed for genome editing
- 13 Here is a CRISPR Timeline:
1. Identification of Repeated DNA sequences
First, Japanese scientist “Yoshizumi Ishino and his group’’ from the University of Osaka in 1987 reported the repeated DNA sequences, while working with IAP gene. They only described the existence of these sequences, at that time, they were not able to find the functions of these sequences.
2. Discovery of the Similar Repeats
In 1993, researchers from the Netherlands, while working on Mycobacterium tuberculosis, reported the presence of repeated sequences, which were intervened by non-repeating sequences. They saw that these repeated sequences were also present in other Mycobacterium species.
3. Discovery of CRISPR and its function
In 1993, a Spanish microbiologist, Francisco Mojica from the University of Alicante, Spain, also observed the repeated sequences, which were interrupted by non-repeated sequences in archaeal species.
Then in 2001-2002, Francisco Mojica and Ruud Jenson coined the term “CRISPR.” Francisco Mojica further discovered that the intervening sequences between repeated sequences were in fact parts of the bacteriophage genome.
In 2005, He succeeded in finding out the function of CRISPR.
4. Discovery of Cas9 and PAM
In 2005, CAS9 and PAM (protospacer adjacent motifs) were discovered by Alexander Bolotin from French national institute for agricultural research.
He discovered them while working on Streptococcus thermophiles bacteria. He sequenced it and found some novel sequences in its CRISPR locus. These sequences were for Cas9, a nuclease enzyme.
Also, he found out that the spacers or intervening sequences shared some homology with viral genes. While a set of nucleotide were common across all spacer’s sequences present at one of the ends. They were called PAM or protospacer adjacent motifs, which was used as target recognition by CRISPR.
5. Hypothetical scheme of adaptive immunity
March 2006, Eugene Koonin from US National Center for Biotechnology Information, NIH, hypothesized how CRISPR works in adaptive immunity.
6. Experimental demonstration of adaptive immunity
March 2007 — Philippe Horvath from Danisco France SAS, experimentally demonstrated the working of CRISPR as adaptive immunity.
7. Spacer sequences are transcribed into guide RNAs
August 2008 — John van der Oost from University of Wageningen, Netherlands showed that spacer sequences acquired from viruses are transcribed into RNAs upon invasion.
Video: Was CRISPR Discovered or Invented?
8. CRISPR acts on DNA targets
December 2008 — Luciano Marraffini and Erik Sontheimer, from Northwestern University, Illinois showed that CRISPR acts on DNA and cleave them. Later it was found that some type of CRISPRs also acts on RNA instead of DNA.
9. Cas9 cleaves target DNA
December 2010 — Sylvain Moineau from University of Laval, Quebec City, Canada showed that CAS9 is a DNA nuclease and it cleaves DNA
10. Discovery of tracrRNA for Cas9 system
March 2011 — Emmanuelle Charpentier, Umea University, Sweden and University of Vienna, Austria, discovered another component of CRISPR system, Trans-activating CRISPR RNA, or tracrRNA.
11. Biochemical characterization of Cas9-mediated cleavage
September 2012 — Virginijus Siksnys, Vilnius University, Lithuania, He did a set of experiments on CRISPR, to find out its mode of action and how it recognizes a specific sequence.
June 2012 — Charpentier and Jennifer Doudna, University of California, Berkeley, they both reported that crRNA and tracrRNA both can be fused together, so to make gene-editing easier.
12. CRISPR-Cas9 harnessed for genome editing
January, 2013 — Feng Zhang, from Broad Institute of MIT and Harvard, McGovern Institute for Brain Research at MIT, Massachusetts. He showed that the CRISPR system can be programmed to be used as a gene-editing tool. Also, it can be used in higher organisms, as he used it in humans and mouse cell lines.
Here is a CRISPR Timeline:
Explore More: Scientists find new and smaller CRISPR gene editor: CasX