CRISPR is a promising treatment in many previously untreatable or hard to treat medical cases, such as cancer, viruses, HIV and countless others. This blog post will be focusing on targeting cancer with CRISPR/Cas9. The goal for this treatment is targeting precise nucleotide sequences in the genome. This is not limited to CRISPR, however CRISPR is the most powerful while offering a great amount of control.
Cancer presents many problems when looking for treatment options. Because cancer occurs with a mutated strand of DNA that can result in tumors the mutation can be in differing places in different patients, making a single form of treatment next to impossible, considering each case is different. A popular and effective form for cancer treatment is chemotherapy. The goal of this treatment is to target cells that are dividing (mutating) out of control and kill them. (Hair cells divide quite fast which is why people lose hair undergoing these treatments.)
As mentioned in the previous post CRISPR targets specific areas within the genome while Cas-9 cuts the DNA strand. Looking at this with more detail in the application, the gRNA (guide RNA) is what gets Cas-9 to the targeted area. gRNA consists of 20 base pair guide sequence nucleotides. gRNA also contains Protospacer Adjacent Motif (PAM) which is a smaller base pair (between 2-6 nucleotides) that follow at the end of the gRNA. PAM helps make sure the targeted section is in fact the targeted section. Once the gRNA has guided Cas-9 to its place Cas-9 then makes the cut, this is a Double Stranded Break 3-4 nucleotides after PAM (DSB, meaning it breaks both strands of DNA). Then the repairing can begin. There are two ways that this can occur. 1, DSB is fixed by Non-Homologous End Joining (NHEJ) systems of repair. This is where a nucleotide could be inserted/deleted (InDels), NHEJ is effective however is inclined toward errors, such as a stop codon or frameshift. 2, is repairing the DSB by using Homology Directed DNA Repair (HDR) this serves as donor DNA, which is much less likely to result in error. Example can be seen below.
Bibliography
White, Martyn K, and Kamel Khalili. “CRISPR/Cas9 and Cancer Targets: Future Possibilities and Present Challenges.” Oncotarget, Impact Journals LLC, 15 Mar. 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC4914286/.
This is great! I'm actually working on a CRISPR lab project in my bio class right now. We're deleting the lacZ gene in E. Coli bacteria using homology directed-repair. It's crazy how 10 years ago this tech had just emerged and now it's being used for labs in undergraduate classes.
ReplyDeleteThat is awesome! I am so glad to hear that you are working on it. What school are you at? I hope to be doing lab research soon but Covid makes that difficult.
DeleteSuper cool post! I wonder where well be in 10 more years??
ReplyDeleteThe diagrammes remind me of splicing electrical wire, which is a useful metaphor for the non-science-minded like me, though I know it's highly reductive.
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