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CRISPR-Cas genome editing

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CRISPR-Cas genome editing is a technique that can be used to add, subtract, or change genetic information in a genome. It uses repeating genetic sequences known as CRISPR from bacteria. The CRISPR/Cas9 genome editing method was developed in 2012 at the University of California in Berkeley. The process forms a special kind of guide RNA that targets the Cas9 enzyme to a specific region in the genome. The enzyme can cut the DNA at this site and insert new genetic information using a plasmid. This targeting system makes the CRISPR/Cas9 method much more precise and effective than previous techniques. This type of genome editing has been used on a variety of different species and has shown the potential to help treat several human diseases, such as hemophilia, sickle cell anemia, HIV, and cancer. CRISPR/Cas genome editing has become a very controversial topic. There has been much debate over the ethical implications and possible risks of its use, especially as it relates to humans.

History

Jennifer Doudna is one of the scientists who developed CRISPR/Cas9.

In the 1980s, Japanese researchers found a series of short, repeating sequences of DNA while looking at a gene in a sample of E. coli bacteria. In between the repeating DNA they found spacers, genetic sequences that do not repeat. In the next few years, this genetic pattern was discovered in other species of bacteria. Eventually, scientists learned that these genetic sequences, together with Cas, or CRISPR associated, enzymes and RNA, function as part of the immune systems of bacteria. [1] [2] This genetic pattern was given the name CRISPR, which comes from an acronym that stands for "clustered regularly interspaced short palindromic repeats".[1]

The development of the CRISPR/Cas9 genome editing technique began in 2012. The study occurred at the University of California in Berkeley and was done by Jennifer Doudna and Emmanuelle Charpentier. In the past, scientists have used techniques such as zinc finger nucleases and TALENS. However, in both of these techniques, new kinds proteins must be formed. The CRISPR/Cas9 genome editing technique, which does not require the creation of unique proteins, arose as a much simpler and more efficient method of genetic engineering. [1]

How It Works

A chart showing how the Cas9 protein and RNA edit DNA

In the CRISPR/Cas9 mechanism most often used, pieces of DNA from plasmids (circular molecules of DNA usually from bacteria) or viruses are placed inside the the CRISPR site of a bacterium.[3][4] CrRNA, a special kind of RNA molecule that can target DNA with a specific gene pattern, is created through the process of transcription. It combines with a complementary RNA molecule called tracrRNA[3] Together, these two kinds of RNA form guide RNA.[5]CrRNA, tracrRNA,and the Cas9 endonuclease, an enzyme that can cut internal bonds of nucleotides in a DNA molecule, are the factors involved in CRISPR/Cas9 genome editing.[3][6]

The guide RNA targets the Cas9 enzyme to the genetic sequence that is to be cut.[5]Scientists can program it for the desired target.[2] The Cas9 processes the RNA and cuts the target DNA.[3] After slicing the DNA, the Cas9 can insert new genetic information into the DNA using a plasmid.[5] These genes are placed in the spacers between the repeating segments of DNA.[7]


Applications

CRISPR/Cas9 genome editing can be used for a variety of different purposes. This gene editing technique can be used to insert, delete, or rearrange genetic information in the genome. CRISPR/Cas9 has been used to edit the genomes of several different species, such as bacteria, Drosophilia, mice, monkeys, pigs, rats, zebrafish, and even humans.[3] With CRISPR/Cas9, scientists can insert genes into animals that make them useful for studying human illnesses. It can also be used to create better genetically-modified crops and livestock.[8]

The CRISPR/Cas9 genome editing method shows promise for curing human disease. In mice, it has been used to heal muscular dystrophy and liver disease. CRISPR/Cas9 can treat sickle cell anemia and hemophilia in humans and help cancer cells respond better to chemotherapy.[9][8] It has demonstrated an ability to deactivate the HIV virus in human cells.[10] In addition, CRISPR/Cas9 can introduce changes into the germ line by adding DNA sequences into an embryo. These genetic changes can be passed down to future generations.[8]

Ethical Concerns

As CRISPR-Cas9 rapidly develops, several researchers, several researchers are starting to consider the ethical implications of using this technology.This is especially important in its application to humans.[8] Many people believe ethical guidelines for using CRISPR/Cas9 should be set.[11] One ethical concern is that some people might attempt to use CRISPR/Cas9 to produce humans with superior traits instead of just for curing genetic diseases. This could lead to the creation of what many refer to as "designer babies".[1]

Another concern is that scientists are still unsure about the effect this genome-editing technique will have on humans.[8] In China, an experiment was done using CRISPR/Cas9 in an attempt to correct a genetic disorder in several embryos, but very few of them survived. This suggests that CRISPR/Cas9 is currently too dangerous to be used on humans. In addition, because CRISPR/Cas9 affects germ cells, any problems that it causes can be passed down to future generations.[11] Because of such concerns, the National Institute of Health has refused to fund the use of CRISPR/Cas9 on humans, and several conferences will be held to discuss ethical issues associated with this genome-editing technique.[1]

Video

A video that explains how CRISPR/Cas9 genome editing works

References

  1. 1.0 1.1 1.2 1.3 1.4 Yin, Steph. What Is CRISPR/Cas9 and Why Is It Suddenly Everywhere? Motherboard. Web. Published on April 30, 2015.
  2. 2.0 2.1 Zhang, Sarah. Everything You Need to Know About CRISPR, the New Tool that Edits DNA Gizmodo. Web. Published on May 6, 2015.
  3. 3.0 3.1 3.2 3.3 3.4 Reis, Alex; Hornblower, Breton; Robb, Brett; and Tzertzinis, George CRISPR/Cas9 and Targeted Genome Editing: A New Era in Molecular Biology New England BioLabs, Inc.. Web. Accessed on March 18, 2016 .
  4. Plasmid/plasmids Scitable. Web. Accessed on March 19, 2016. Author unknown.
  5. 5.0 5.1 5.2 Genome Editing Allele Biotechnology. Web. Accessed on March 19, 2016. Author unknown.
  6. Endonuclease The Free Dictionary. Web. Accessed on March 19, 2016. Author unknown.
  7. Patel, Navita. CRISPR-genome editing WINGD. Web. Accessed on March 19, 2016.
  8. 8.0 8.1 8.2 8.3 8.4 Gomez Tatay, Lucia Genome editing CRISPR-Cas9. Biomedical and ethical considerations Bioethics Research Library . Web. Published February 3, 2016.
  9. CRISPR/Cas9 Genome-Editing Technology Intellia Therapeutics. Web. Accessed March 28, 2016. Author unknown.
  10. Grens, Kerry. Genome Editing Cuts Out HIV The Scientist. Web. Published July 21, 2014.
  11. 11.0 11.1 Stockton, Nick. America Needs to Figure Out the Ethics of Gene Editing Now Wired. Web. Published April 23, 2015.