Using CRISPR-Cas9 for Genetic Diseases

            The advancement in gene technology has been rapidly increasing, and the most recent break through is the discovery of CRISPR. This specifically stands for “clustered regularly interspaced short palindromic repeats”. CRISPR was acquired from bacteria and then modified to CRISPR-Cas9 for laboratory uses. It became a huge step in biology because it was discovered to be able to edit genes and from this finding scientist began to explore ways to use it to remove or replace genes, turn of or on genes, and insert new ones (Hobbs, 2016).

            The way that CRISPR-Cas9 works is that it is composed of RNA which can be perfectly matched with a sequence of DNA (Hobbs, 2016). Since it can be ideally matched to DNA, it makes it that much easier to prevent mismatching errors and improves its accuracy when targeting specific genes. Designing it this way allows it to attach to the target DNA sequence and cut or change it at the same time. There are various experiments being done in the world with the application of CRISPR-Cas9, but the most interesting one is how it can be used towards genetic diseases. This can be accomplished through NHEJ or HDR gene editing. NHEJ stands for non-homologous end joining, which is insertions or deletions to the gene, and HDR stand for homology-directed repair, which is a gene sequence substitution. Still to this day it is being tested for correcting genetic sequences that are responsible for genetic diseases through various models. Some of the main diseases that are of interest are cataracts, cancer, hepatitis B, and high cholesterol.

            Mice have been used in a study to see if CRISPR-Cas9 can combat the genetic disease of cataracts. When mice have cataract disease their vision becomes impaired and blurred due to a gene that causes the lens in the eyes to get very opaque. The gene that causes this mutation is Crygc. The goal of the study was to inject CRISPR-Cas9 into zygotic mice that had these mutation and see if the corrections made in the alleles were passed down to their offspring. The mice chosen for this experiment had a “1bp deletion in exon 3 of Crygc and used single-guide RNAs (sgRNAs) to specifically target different regions in the mutation (Wu, Yuxuan et al., 2013). After several trials it was found that sgRNA-4, which targeted the region below the 1bp deletion, was actually targeting the mutant allele (Wu, Yuxuan et al., 2013), meaning that the region below the 1bp deletion was the one containing the mutant allele. The researchers then used sgRNA-4 to see if there could be a difference made on the phenotype of cataracts. It was concluded that CRISPR-Cas9 can actually be used to alter DNA sequences to correct them through the application of NHEJ- or HDR-medicated gene editing.

            This is an interesting topic because it proves that the increase in technology and knowledge of science is bringing about new ideas that can benefit humans in the long run. Since it is fairly a new system, studies over how it can cause any harmful side effects still need to be conducted. There seems to be an innovative future with CRISPR-Cas9 because it is also be used for stem-cell renewal, host protection against virus replication, and phenotype altering such as eye and hair color. Most importantly it could potentially be the answer to genetic diseases with further studies and alterations to the system. 

References

Hobbs, Bernie. “CRISPR: The New Tool in the Gene Editing Revolution Explained.” ABC News, Australian Broadcasting Corporation, 12 Apr. 2016, www.abc.net.au/news/science/2016-04-07/crispr-gene-editing-technology-explainer/7217782. 

Wu, Yuxuan et al. “Correction of a Genetic Disease in Mouse via Use of CRISPR-Cas9.” Vol. 13, no. 6, 5 Dec. 2013, pp. 659–662., www.cell.com/cell-stem-cell/fulltext/S1934-5909(13)00462-1.