This paper will introduce the technical implementations of CRISPR Cas 9 as well as the future of Genome Editing with CRISPR Cas 9. Though this paper will mainly focus on the technological facts of Genetic Engineering methods, some ethical issues will also be discussed.
CRISPR protein based genome editing methods, among all genome editing technologies, is doubtlessly the most effective and precise genetic editing method. Nevertheless, the more powerful this technology became, just like many other genetic engineering technologies, the more ethical challenges that this technology is facing. In fact, despite all the debates among scientists, Genome Editing on humans are strictly banned in the United States. Regardless, CRISPR protein-based genetic editing still shows a bright future in Applied Science and Molecular Biology.
1. Genetic Engineering
Genetic Engineering has been the most popular topic in Biology not just recently. As a matter of fact, the term Genome Editing may sound like a cutting-edge and futuristic technology that frequently appears in science fiction movies — military uses this technology to produce super soldiers, villains use it to breed monsters, and heroes depend on it to gain superpowers — artificial genetic engineerings have existed long before the formation of clustered population or the beginning of civilization. Nevertheless, most genetic engineering technologies that had appeared before are based on Artificial Selection. With Artificial Selection, in contrast to Natural Selection, people actively select and breed the crops or domestic animals with the most helpful traits and phenotype (Corner, 2003, p.1). Our ancestors have used this method to increase their production in crops and breed some amazing offsprings of animals.
Today, with the rapid development of technology and many breakthroughs in Molecular Biology, DNA editing has become more and more popular in the field of genetic engineering. Comparing to Traditional Artificial Selection methods, genome editing allows people to not only select the best trait of species based on their phenotypes, but also the potentially beneficial allele in a species genotype, which is sometimes not present in the species phenotype. Moreover, modern genome editing technologies, including CRISPRs and TALEN, with the help from DNA sequencing technologies developed in the past few decades, even allow people to edit the genotype of a living body without the need to reproduce, which potentially could be used to treat cancers and hereditary diseases (Lundberg, 2015).
2. Selective Breeding
Humans have a long history of conducting Artificial Selection on other species. The most adorable species and human’s best friend: dogs are results of Selective Breeding. Originated from Gray Wolf, Canis lupus, the dogs available on the markets are better known as Canis lupus familiarus (Mayabasu, 2013). Similar to genetic editing, Selective Breeding changes the original genetic sequence by letting the individual with the most helpful traits reproduces, resulting in a population with the traits that the breeder wanted. Yet different from genetic editing, Selective Breeding does not introduce any new DNA sequence to the species: all the changes in traits are results of the variation within the population of that species (New Zealand Science Media Centre, 2008).
Nevertheless, there are many downsides of Selective Breeding. Firstly, similar to Natural Selection, Selective Breeding takes a long time, usually several generations, to change the gene pool of a specie. According to an article published by Price on Science, at the rate of 7 years per generation, it took around 700 years to breed the modern horses (2017). Secondly, Selective Breeding usually involves the reproduction of close relatives within a species, since the genetic pool of a smaller population is relatively easier to change. While interbreeding significantly accelerates the process of breeding, this also increases the chances of genetic diseases and decreases the variation of the gene pool. Studies have concluded that interbreeding significantly increases the fertility rate of eggs and causes a series of interbreeding depression (Cheng, 1993). Lastly, some ethical issues seem to have risen with Selective Breeding. Since reproduction is the key part of selective breeding, animals are usually forced to reproduce. Moreover, in most cases offsprings are isolated from the bigger population and usually their birth parents.
3. Genome Editing with CRISPR proteins
Instead of utilizing the variation within the population, Modern Genetic Engineering methods directly modifies the original genetic sequences, which is more efficient and precise comparing to Selective Breeding, and changes are usually more predictable and controllable. Among all the techniques of Genome editing, CRISPR Cas 9 is relatively new. Nevertheless, this technology has attracted tremendous attention recently (Dy, 2017).
Clustered Regularly Interspaced Short-Palindromic Repeats system is originally found in prokaryotic bacterias as part of their immune system against viruses (Barrangou, 2007). The CRISPR system in bacteria produces Cas9 proteins that each contains two RNAs transcribed from the immune system itself (crRNA and tracrRNA, synthesis to form gRNA or sgRNA). One of them (crRNA) contains a strip of information, which are the genetic sequences of viruses that have been identified by Cas1-Cas2 proteins (Nuñez et al., 2014). The Cas9 protein then works by unzipping the double strand DNA sequences it found elsewhere in the bacteria and matches it with the guidance RNA. Once the sequence successfully matches the guidance RNA, Cas9 protein will cut the DNA, hoping to disable the DNA. As a matter of fact, when the DNAs are damaged, cells will try to repair them. Normally the sequence will be disabled or mutate, but if another sequence that fits the cutting points is present at the same time, that piece of DNA can be inserted to the breaking point (McGovern Institute for Brain Research at MIT, 2014).
Since the CRISPR Cas 9 protein can cut DNAs with precision not only in the test tube but also in a living body cell’s nucleus, this mechanism provides great flexibility for researchers. For example, xenotransplantation from pigs has not been possible but a dream for many scientists because of human immunological resist and porcine endogenous retroviruses (PERVs) inside pigs’ genes that can potentially infect humans. Groups of researchers recently published their discoveries: by using Cas 9 proteins on the embryos of pigs, they successfully deactivated the piece of the gene that produces the PERVs (Liu et al., 2017).
Moreover, CRISPR Cas 9 is easier and cheaper to use. A complete CRISPR Cas 9 kit can be found online with a price tag only at $159 (DIY Bacteria, n.d.). In addition, an experiment conducted in an undergraduate class prove that CRISPR Cas 9 is, in fact, feasible to be completed by even amateur scientists (Adame et al., 2016).
The only questions remain are mostly related to ethics. With the Cas 9 being well studied for human and animal cells, no public reports have been published. In fact, a few scientists reported by the Nature News have studied the effects of CRISPR Cas 9 on human embryos, but their paper was rejected by both the Science magazine and Nature magazine. With such a powerful tool in hand, it is unknown what people can do with human embryos (Cyranoski & Reardon, 2015). In fact, it is unknown how many research institutes are now working on human genetic modifying with CRISPR Cas 9.