Rewriting the Blueprint
Gene editing for improved agriculture, healthcare, and beyond.
Study Resources & Key Ideas
How does this all work exactly?
CRISPR-Cas9
Clustered regularly interspaced short palindromic repeats (CRISPR) and its corresponding protein (Cas 9) have stirred much excitement in the biotechnology fields--namely, the biomedical engineering sector. CRISPR-Cas 9 serves as an efficient and cheaper way to carry out genomic editing. Naturally found in bacteria, this system can be used to identify and create double-stranded breaks (DSBs) in DNA. Geneticists can engineer a guide RNA (sgRNA) strand to target a specific problem sequence--whether virally infectious or causing genetic-related health complications. When combined with the Cas 9 nuclease, the system can be directed to the problem site and perform a DSB. If the break is in viral DNA, CRISPR-Cas 9 will disable, or 'turn off' the infectious gene, storing it in the cell’s memory as CRISPR arrays to protect against future encounters with the virus. If the break occurs in human DNA, scientists can insert modified gene sequences to remedy the problem gene or utilize the cell’s internal DNA repair systems.
Watch the videos below for more information.
TALENs
TALENs are composed of non-specific FokI DNA cleaving nuclease plus unique binding domains (transcription activator-like effectors (TALEs)) made from proteins with a repeating code secreted by Xanthomonas bacteria.TALEs, DNA-binding domains function by utilizing a tandem of repeats, each 33-34 amino acids long--identical apart from amino acids 12 and 13, known as RVDs (repeat variable diresidues), which identify specific bases. The repeats locate desired DNA sections for double-stranded breaks using the FokI nucleases of two TALENs systems, one on each side of the target gene. This modular system allows for TALEs to be engineered for specific sequences in genome editing. TALENs can be inserted into an organism via a plasmid or an mRNA vector. Using the latter favors success in gene editing by increasing the homology-directed repair (HDR) since mRNA reduces the likelihood of a TALEN protein being expressed in the organism’s genome.
Traditional Viral Vectors
Before the discovery of CRISPR and TALENs, many scientists used viral vectors for gene therapies. This is when a deactivated virus is used as a delivery medium for a modified gene in an organism. The viral vector containing the new gene(s) can be injected and directly introduced to a patient's body (in-vivo), or cells can be exposed to the vector ex-vivo, then returned to the patient's body. Examples of viral vectors include retroviruses (can "permanently integrate" DNA into mitotically dividing cells), adenoviruses (can introduce DNA into dividing and non-dividing cells), and herpes simplex viruses (can transfer larger amounts of genetic material) (SC.7).
Stem Cells in Gene Therapy
Stem cells are non-specific cells that can specialize into virtually any cell type. They are found in abundance during early embryonic development stage and have been of much interest for therapy and cloning. Stem cells can be used to repair damaged tissue such as those of severe burn victims, or in regenerative medicine. Recently, however, scientists have been studying ways in which they can also be used in gene therapy.
Embryonic Stem Cells
ESCs are found and collected from embryos--typically those donated or discarded after in-vitro fertilization (IVF) procedures. There is, however, much debate over whether or not it is ethical to use these stem cells since they do come from embryos that had the potential to develop into human beings.
Induced Pluripotent Stem Cells (iPSCs)
Scientists have discovered ways to induce pluripotency into mature, specialized cells. Pluri-what? All this means is that cells have the ability to specialize and form into any type of cell as needed for specific treatments. Many are cautious of these cells however, as there is always the chance that they could revert back to their normal state and cause many complications and setbacks in the treatment process.
Adult Stem Cells
Some cells, including those found in the bone marrow, exist as stem cells which can be isolated from a patient's body and introduced in the necessary area.
In-Vivo vs. Ex-Vivo Treatment
There are two main ways in which genome editing can occur: in-vivo and ex-vivo. In-vivo occurs within an organism's body when modifications are introduced directly into cells/tissues and are left to replicate on their own. Ex-vivo is when scientists extract and isolate cells from an organism, modify them, then insert them back into the organism.
