CRISPR/Cas gene editing system unraveling a DNA strand

CRISPR/Cas gene editing

Expand your understanding of gene editing

CRISPR/Cas systems are driven by a mechanism that is thought to deliver site-specific gene or genome editing, unlocking the possibility of precisely targeting and permanently modifying a genomic sequence through disruption, deletion, correction, or insertion.1-3 By learning how this approach works, you can start to see how far the field of gene editing has come—and where it might be going next.

CRISPR/Cas gene editing system unraveling a DNA strand

CRISPR/Cas gene editing

Expand your understanding of gene editing

CRISPR/Cas systems are driven by a mechanism that is thought to deliver site-specific gene or genome editing, unlocking the possibility of precisely targeting and permanently modifying a genomic sequence through disruption, deletion, correction, or insertion.1-3 By learning how this approach works, you can start to see how far the field of gene editing has come—and where it might be going next.

CRISPR/Cas gene-editing process

CRISPR/Cas system components

Most CRISPR/Cas systems have 2 key components that get delivered to a patient’s cells1,4,5:

  • Single guide RNA (sgRNA)
  • CRISPR-associated (Cas) nuclease bound to sgRNA
CRISPR/Cas system single-guide RNA and CRISPR-associated nuclease
CRISPR/Cas system single-guide RNA and CRISPR-associated nuclease

Finding the right sequence

The pre-programmed sgRNA targets a specific sequence in the genome, and then the Cas nuclease begins unraveling the DNA.1,4-6

CRISPR/Cas system single-guide RNA finding sequence in genome and Cas nuclease unraveling a DNA strand
CRISPR/Cas system single-guide RNA finding sequence in genome and Cas nuclease unraveling a DNA strand

Base pairing of sgRNA and DNA

Once the DNA is unraveled, the sgRNA can base pair with its complementary strand of target DNA.6

CRISPR/Cas system single-guide RNA base pairing with its complementary strand of DNA
CRISPR/Cas system single-guide RNA base pairing with its complementary strand of DNA

Breaking the DNA

The Cas nuclease creates a double-strand break in the DNA at the targeted site, which then activates natural cellular repair and enables modification of the gene or its function.1,4,5

The location of the double-strand break depends on the CRISPR system type.7

CRISPR/Cas system creating a double-strand break in DNA
CRISPR/Cas system creating a double-strand break in DNA

Repairing the DNA break

After the Cas nuclease creates a double-strand break, the DNA is repaired in 1 of 2 ways1,5,8:

  1. Nonhomologous end joining (NHEJ) results in insertions or deletions (indels) of base pairs at the target site
  2. Homology-directed repair (HDR) involves insertion or correction via a DNA template at the target site
CRISPR/Cas system moving away from a repaired DNA strand
CRISPR/Cas system moving away from a repaired DNA strand

Disrupting, deleting, correcting, or inserting genes

Depending on the repair mechanism, gene editing can result in:

Gene editing icon representing gene disruption

Gene disruption

NHEJ repairs DNA double-strand break, generating insertions or deletions that disrupt or inactivate the gene.6,9,10

Gene editing icon representing gene deletion

Gene deletion

Two double-strand breaks of the DNA are simultaneously generated, removing an intervening DNA segment encoding the gene.6

Gene editing icon representing gene correction or insertion

Gene correction or insertion

HDR donor template corrects gene function or inserts functioning genetic material into the gene.6,9,10

Broaden your knowledge base

Be prepared to answer gene-therapy questions from patients. Check out our curated selection of links to published articles and other educational resources.

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Check out our gene-therapy timeline to see how far the field has come.

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References:  1. Uddin F, Rudin CM, Sen T. CRISPR gene therapy: applications, limitations, and implications for the future. Front Oncol. 2020;10:1387. doi:10.3389/fonc.2020.01387.  2. Doudna JA, Charpentier E. The new frontier of genome engineering with CRISPR-Cas9. Science. 2014;346(6213):1258096. doi:10.1126/science.1258096.  3. Prakash V, Moore M, Yáñez-Muñoz RJ. Current progress in therapeutic gene editing for monogenic diseases. Mol Ther. 2016;24(3):465-474. doi:10.1038/mt.2016.5.  4. Li H, Yang Y, Hong W, Huang M, Wu M, Zhao X. Applications of genome editing technology in the targeted therapy of human diseases: mechanisms, advances and prospects. Signal Transduct Target Ther. 2020;5(1):1. doi:10.1038/s41392-019-0089-y.  5. Chemello F, Bassel-Duby R, Olson EN. Correction of muscular dystrophies by CRISPR gene editing. J Clin Invest. 2020;130(6):2766-2776. doi:10.1172/JCI136873.  6. Gaj T, Sirk SJ, Shui SL, Liu J. Genome-editing technologies: principles and applications. Cold Spring Harb Perspect Biol. 2016;8(12) :a023754. doi:10.1101/cshperspect.a023754.  7. Banakar R, Schubert M, Collingwood M, Vakulskas C, Eggenberger AL, Wang K. Comparison of CRISPR-Cas9/Cas12a ribonucleoprotein complexes for genome editing efficiency in the rice phytoene desaturase (OsPDS) gene. Rice. 2020;13(1):4. doi:10.1186/s12284-019-0365-z.  8. Dunbar CE, High KA, Joung JK, Kohn DB, Ozawa K, Sadelain M. Gene therapy comes of age. Science. 2018;359(6372):eaan4672. doi:10.1126/science.aan4672.  9. Adli M. The CRISPR tool kit for genome editing and beyond. Nat Commun. 2018;9(1):1911. doi:10.1038/s41467-018-04252-2.  10. Guha TK, Wai A, Hausner G. Programmable genome editing tools and their regulation for efficient genome engineering. Comput Struct Biotechnol J. 2017;15:146-160. doi:10.1016/j.csbj.2016.12.006.