CRISPR—Revolutionizing Genome Editing

A new form of genome editing (i.e., the site-directed deletion, addition, or insertion of chromosomal DNA by nuclease enzymes)—CRISPR/ Cas9—is the subject of the current biotechnological leap. CRISPR stands for clustered regulatory interspaced short palindromic repeats, referring to the tiny stretches of viral DNA that some bacteria carry in their genomes (Zhang, Wen, and Guo 2014). These viral snippets, and the proteins associated with them, make up a primitive adaptive immune system, allowing bacteria to recognize and destroy invading viral DNA. Naturally occurring CRISPR systems were first reported in 1987, when researchers stumbled upon an oddly repetitive series of sequences in a bacterial gene (Pennisi 2013). It wasn’t until 2005, when sequence comparisons revealed similarities between these kinds of repetitive elements and viral genomes (Pennisi 2013). Not long after, the first functional study of a CRISPR system was published by researchers at Danisco food company (Barrangou et al. 2007). Independent researchers from the United States and Germany, Jennifer Doudna and Emmanuelle Charpentier, saw CRISPR’s potential. Their teams worked together to develop CRISPR into a genetic tool (Ledford 2015a; Pennisi 2013), resulting in a landmark paper in 2012 (Jinek et al. 2012). Since then, CRISPR/Cas9 has quickly taken over the genome-editing scene, by outperforming the previous technologies; zinc finger and transcription activator-like effector nucleases (ZFNs; TALENs) (Ledford 2015a; Pennisi 2013).

Since CRISPR uses nucleic acids (rather than proteins) to hone in on genomic targets, it is a financially accessible technology. Reagent costs are just a fraction ($30 vs. $5,000) of those associated with traditional approaches (Ledford 2015a). As such, the number of scientific articles mentioning CRISPR technology has grown exponentially since 2013, while reports about ZFNs and TALENs have leveled off (Ledford 2015a). CRISPR was even featured on the cover of the June 2016 issue of TIME Magazine, with the caption, “The Gene Machine: What the CRISPR experiments mean for humanity.” Other recent headlines online and in print include “CRISPR May Work On Way More Diseases Than We Think” (Park 2016) and “Easy DNA Editing Will Remake the World. Buckle Up” (Maxmen 2015). The molecular details of CRISPR/Cas9 and its current and future applications are explored in Chapters 2, 3, and 4.

Box 1.2. Challenge integration exercise: Timeline

Using information from the previous sections, create a timeline of the major historical events in the development of rDNA technologies, DNA sequencing, organismal cloning, and CRISPR. What decades are associated with major biotechnological advances? What else was going on in the world as key biotechnologies emerged?

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