Friday, August 4, 2017

Basics of CRISPR Research

Clustered regularly interspaced short palindromic repeats (CRISPR) are segments of prokaryotic DNA containing short, repetitive base sequences. These play a key role in a bacterial defence system, and form the basis of a genome editing technology known as CRISPR/Cas9 that allows permanent modification of genes within organisms. In a palindromic repeat, the sequence of nucleotides is the same in both directions. Each repetition is followed by short segments of spacer DNA from previous exposures to foreign DNA (e.g., a virus or plasmid). Small clusters of cas (CRISPR-associated system) genes are located next to CRISPR sequences.

The CRISPR/Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages that provides a form of acquired immunity. RNA harboring the spacer sequence helps Cas proteins recognize and cut exogenous DNA. Other RNA-guided Cas proteins cut foreign RNA. CRISPRs are found in approximately 40% of sequenced bacterial genomes and 90% of sequenced archaea.

A simple version of the CRISPR/Cas system, CRISPR/Cas9, has been modified to edit genomes. By delivering the Cas9 nuclease complexed with a synthetic guide RNA (gRNA) into a cell, the cell's genome can be cut at a desired location, allowing existing genes to be removed and/or new ones added. The Cas9-gRNA complex corresponds with the CAS III crRNA complex in the above diagram.

CRISPR/Cas genome editing techniques have many potential applications, including medicine and crop seed enhancement. The use of CRISPR/Cas9-gRNA complex for genome editing was the AAAS's choice for breakthrough of the year in 2015. Bioethical concerns have been raised about the prospect of using CRISPR for germline editing.


By the end of 2014 some 600 research papers had been published that mentioned CRISPR. The technology had been used to functionally inactivate genes in human cell lines and cells, to study Candida albicans, to modify yeasts used to make biofuels and to genetically modify crop strains. CRISPR can also be used to change mosquitos so they cannot transmit diseases such as malaria.

CRISPR-based re-evaluations of claims for gene-disease relationships have led to the discovery of potentially important anomalies.

Policy Barriers to Genetic Engineering

Policy regulations for the CRISPR/cas9 system vary around the globe. In February 2016, British scientists were given permission by regulators to genetically modify human embryos by using CRISPR-Cas9 and related techniques. However, researchers were forbidden from implanting the embryos and the embryos were to be destroyed after seven days.

The US has an elaborate, interdepartmental regulatory system to evaluate new genetically modified foods and crops. For example, the Agriculture Risk Protection Act of 2000 gives the USDA the authority to oversee the detection, control, eradication, suppression, prevention, or retardation of the spread of plant pests or noxious weeds to protect the agriculture, environment and economy of the US. The act regulates any genetically modified organism that utilizes the genome of a predefined 'plant pest' or any plant not previously categorized. In 2015, Yang successfully deactivated 16 specific genes in the white button mushroom. Since he had not added any foreign DNA to his organism, the mushroom could not be regulated under by the USDA under Section 340.2. Yang's white button mushroom was the first organism genetically modified with the Crispr/cas9 protein system to pass US regulation. In 2016, the USDA sponsored a committee to consider future regulatory policy for upcoming genetic modification techniques. With the help of the US National Academies of Sciences, Engineering and Medicine, special interests groups met on April 15 to contemplate the possible advancements in genetic engineering within the next 5 years and potential policy regulations that would need to come into play. With the emergence of rogue genetic engineers employing the technology, the FDA has begun issuing new regulations

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