CRISPR/Cas9 Technologies

SECTION I - DEFINITION & MOLECULAR MECHANISMS

               Clustered Regularly Interspaced Short Palindromic Repeats and enzyme CRISPR-associated endonuclease (Cas9) are commonly referred to as CRISPR/Cas9 technologies.  The company CRISPR Therapeutics refers to Cas9 “as the ‘molecular scissors’ that cut and edit, or correct, disease-associated DNA in a cell.”⁽¹⁾  This technology, while still in its early stages of development, has the potential to chemically edit DNA in living organisms with a high level of accuracy.  A CRISPR Therapeutics Press Release states that “since its discovery in 2012, data on the CRISPR-Cas9 gene editing system have been published in more than 1100 scientific and medical journals supporting its potential applicability to cure serious human diseases that cannot be addressed with existing technologies. The Science Magazine just named the CRISPR gene-editing technology ‘Breakthrough of the Year 2015’.”⁽¹⁾

Artist’s depiction of Cas9 enzymes providing a catalyst for rewriting of DNA.⁽²⁾

                Genetic maladies manifest themselves through protein construction (or lack thereof) based on DNA blueprints that have either been inherited or altered through various natural means.  Hemophilia in particular prevents the body from producing blood clotting factors, which can cause excessive bleeding, bruising, and other dangerous or uncomfortable side effects.  This disorder is inherited and afflicts individuals for their entire lives, often requiring expensive clotting factor transfusions and medications.  CRISPR/Cas9 technologies have the potential to correct errors in clotting factor synthesis to cure hemophilia.  It also has the potential to cure some types of blindness and congenital heart disease in vivo (in living organisms).

                Cas9 is the enzyme used in these new genetic editing technologies.  The enzyme evolved as a mechanism in ancient bacteria to defend against infection.  When these bacteria defeat a viral infection, DNA from the invading virus is incorporated into the host bacterium’s genetic code in what are known as spacer sequences.  Spacers serve as an immune system memory the organism can use to defeat infections with the same genetic sequences.  When a new, genetically unique infection attacks the organism, new spacer sequences are added to the bacterium’s DNA.⁽³⁾

Integration of genetic spacers to be used as immune response sequences.⁽⁴⁾

                Once this genetic defense process was studied, the ability to harness its properties fueled a breakthrough of unprecedented medical utility.  Because of the disruptive nature of the technology, an international conference of scientists was held in December 1 - 3, 2015 in Washington D.C. to discuss its implications, ethical concerns surrounding it, and possible scenarios of how the technology could be applied.⁽⁵⁾

                Controversy surrounds the technology, as its potential for ethical misuse is very high.  The global summit in Washington D.C. was assembled because this is the first time in human history in which a technology with the possibility to alter human (and every other type of) genetic manifestation is available.  Ethical concerns are at the core of the technology and include topics such as designer babies, alteration of genetics that will be passed to the next generation of a species, and the creation of entirely new species of organisms within our biosphere (including agents for biological warfare) which could critically disrupt its homeostasis.

                As research continues, CRISPR/Cas9 has emerged as a possible remedy for many diseases.  According to the MIT Technology Review, “a recently announced $300 million joint venture between Bayer AG and startup CRISPR Therapeutics—to develop new drugs for blood disorders, blindness, and congenital heart disease—is just the latest indication that the pharmaceutical industry is eager to find and develop new cures using CRISPR.”⁽⁶⁾  Current hurdles to implementation involve responsible use of the technology, and a reliable and safe delivery system for the Cas9 enzyme and its genetic payload.




Works Cited:

1.  Paganelli, Jennifer (December 21, 2015).  Press Release.  CRISPR Therapeutics.  Retrieved from http://crisprtx.com/news-events/news-events-press-releases-2015-12-21.php

2.  Cas9 Picture [digital image]. Unknown creator (and posting date).  Retrieved from https://unabridgedmstp.files.wordpress.com/2015/10/art-of-the-cell-crispr-cas9-in-complex-with-guide-rna-and-target-dna.jpg?w=900&h=300&crop=1

3.  Pak, Ekaterina (July 31, 2014).  CRISPR: A game-changing genetic engineering technique.  Harvard.edu.  Retrieved from http://sitn.hms.harvard.edu/flash/2014/crispr-a-game-changing-genetic-engineering-technique/

4.  Spacer diagram [digital image].  Harvard.edu (July 31, 2014).  Retrieved from http://sitn.hms.harvard.edu/flash/2014/crispr-a-game-changing-genetic-engineering-technique/

5.  Reardon, Sara (December 8, 2015).  Global summit reveals divergent views on human gene editing.  Nature.com.  Retrieved from http://www.nature.com/news/global-summit-reveals-divergent-views-on-human-gene-editing-1.18971

6.  Orcutt, Michael (January 13, 2016).  Big Pharma Doubles Down on CRISPR For New Drugs.  MIT Technology Review.  Retrieved from http://www.technologyreview.com/news/545366/big-pharma-doubles-down-on-crispr-for-new-drugs/

SECTION II - ORGANISMAL & POPULATION MANIFESTATIONS

        

      CRISPR/Cas9 is a powerful, but controversial technology for several reasons.  It has the potential to cure disease in individuals, modify organisms in beneficial ways, and can be the scaffolding for sweeping changes in populations using “gene drives.”  Ethical arguments surround CRISPR techniques because modified organisms can pass their genetic information on to future descendants, which can cause the genetic aberration to propagate throughout a population.  The benefit to (not necessarily financial) cost ratio tends to be ambiguous; incredible scientific breakthroughs are possible with CRISPR at an organismal level, but when those breakthroughs are extrapolated within interconnected populations they have the potential to be catastrophic.

      One example of this ambiguous risk to benefit tradeoff is in the application of CRISPR technology to mosquito populations.  Mosquitoes carry the parasite malaria, which caused approximately 584,000 human deaths in 2013.⁽¹⁾  There are two general methods in which mosquitoes could be modified to fight the spread of malaria.

 Anopheles Gambiae, a species of mosquito which is a primary malaria infection vector in Africa.⁽²⁾

 The first method states that “in development are techniques that aim to replace current mosquito populations with those that are pathogen resistant.”  Scientists are skeptical about the effectiveness of this technique because “a primary technical concern of gene-drive-based control strategies is the integrity and long-term stability of any pathogen resistance transgene.”  Over time, the altered genetic material within the organism may repair itself by natural means, rendering the pathogen resistant genetic sequence inert.⁽³⁾

      The second method involves altering sex chromosomes in mosquitoes, releasing them into wild populations, and letting them produce offspring of one gender at an imbalanced rate.  According to a paper published by the National Center for Biotechnology Information, “it has been theorized that inducing extreme reproductive sex ratios could be a method to suppress or eliminate pest populations.”  The author continues by stating that “shredding of the paternal X chromosome prevents it from being transmitted to the next generation, resulting in fully fertile mosquito strains that produce >95% male offspring.  We demonstrate that the distorter male mosquitoes can efficiently suppress caged wild-type mosquito populations, providing the foundation for a new class of genetic vector control strategies.”⁽⁴⁾

⁽⁵⁾

       The first method seems to be the most prudent, in that it has the potential to satisfy its objective of eliminating malaria from mosquito populations but does not adversely interfere with the natural homeostasis of the mosquitoes’ ecosystem.  The second method can be regarded as extremely dangerous; by “suppressing or eliminating pest populations” we run the risk of collapsing the food chain and upsetting the ecosystem in which the modified organism exists.  Spiders, bats, birds, and fish all rely on mosquitoes or their larvae as sources of food; conversely, mosquito larvae consume “algae, plankton, fungi, bacteria, and other microorganisms.”⁽⁶⁾  Completely removing mosquitoes from an ecosystem to combat the spread of malaria introduces a separate set of problems that are not completely quantifiable in a laboratory environment.  The unforeseen, potentially macroscopic second and third order consequences which arise from altering gender ratios in populations outweigh the benefits derived from altering natural processes in this fashion.

      However, there are many immediately positive applications of the CRISPR/Cas9 gene editing technique.  According to John Cramer, reporting in Analog Science Fiction & Fact, “the applications of the CRISPR/Cas9 technique are just beginning to emerge from laboratories around the world.  One can expect that among the first commercial applications will be the production of drug proteins by gene splicing.  This technique began in the 1970s with the production of insulin with recombinant DNA, using a restriction enzyme to cut a bacterial DNA loop and splice in a sequence that produced insulin.  With CRISPR, the production of similar drug proteins becomes much easier and fester [sic] with greatly reduced development costs.”⁽⁷⁾

      It has been postulated that by using CRISPR, the synthesis of other chemical compounds could become cheaper, faster, and more efficient.  For example, by modifying the genetics of yeast or other microorganisms they could be designed excrete compounds such as morphine,⁽⁸⁾ “better biofuels,” and “new enzymes for industrial markets, where they’re used in laundry detergents, water treatment and paper milling.”⁽⁹⁾  The positive possibilities of CRISPR technology are vast, but come packaged with a measure of ambivalence.  In the future as these compounds are produced in laboratories and legal facilities to aid the afflicted and provide more efficient avenues of production, some of them could be produced for illicit purposes.

      The CRISPR debate continues, unabated.  The organismal and population-engineering capabilities of CRISPR are both hope-inspiring and dire.  The technology is poised to influence the smallest molecular constructions in our DNA and has the potential to affect the delicate ecological calculus of our entire biosphere.  Intelligent, careful progression and ethical implementation are all critically important as CRISPR/Cas9 research continues.

Works Cited:

1.  No author listed (December 2014).  Fact sheet on the World Malaria Report 2014.  World Health Organization.  Retrieved from http://www.who.int/malaria/media/world_malaria_report_2014/en/

2.  Anopheles Gambiae [digital image].  Insect Genetic Technologies Research Coordination Network (December 14, 2015).  Retrieved from http://igtrcn.org/gene-drive-in-anopheles-gambiae/

3.  Justin M. Overcash, Azadeh Aryan, Kevin M. Myles, Zach N. Adelman (January 18, 2015).  Understanding the DNA damage response in order to achieve desired gene editing outcomes in mosquitoes.  Chromosome Research.  Retrieved from http://link.springer.com.ezproxy.nu.edu/article/10.1007/s10577-014-9450-8/fulltext.html

4.  Galizi R., Doyle L. A., Menichelli M., Bernardini F., Deredec A., Burt A., Stoddard B. L., Windbichier N., Crisanti A (June 10, 2014).  A synthetic sex ratio distortion system for the control of the human malaria mosquito.  National Center for Biotechnology Information.  Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/24915045?dopt=Abstract#

5.  Drive [digital image, cropped from screenshot].  Insect Genetic Technologies Research Coordination Network (December 14, 2015).  Retrieved from http://igtrcn.org/gene-drive-in-anopheles-gambiae/

6.  No author listed (2014).  Mosquito Biology.  American Mosquito Control Association (AMCA).  Retrieved from http://www.mosquito.org/biology

7.  Cramer, John G. (December 2015).  Genome Editing: The CRISPR Revolution (135.12, pg. 75-77).  Analog Science Fiction & Fact.  Retrieved from http://ezproxy.nu.edu/login?url=http://search.proquest.com/docview/1728220337?accountid=25320

8.  Dizikes, Peter (May 19, 2015).  New potential for “homemade” opiates raises oversight issues.  Phys.org.  Retrieved from http://phys.org/news/2015-05-potential-homemade-opiates-oversight-issues.html

9.  Kahn, Jennifer (November 9, 2015).  The Crispr Quandary.  New York Times.  Retrieved from http://www.nytimes.com/2015/11/15/magazine/the-crispr-quandary.html?_r=0