would specifically target this adenosine, in vitro correction of the premature termination codon could be corrected while minimizing unwanted mutations at other adenosines in the RNA (12). Testing in frog oocytes revealed that after applying this technique, an average of 20% of the RNA was corrected with no noticeable offtarget editing. In addition, properly glycosylated CFTR proteins were detected, and CFTR-mediated currents were partially restored to about half the current levels of wild type CFTR (12). The ability to correct genetic mutations by editing mRNA is appealing for many reasons. First, mRNA is far more accessible than DNA. Genomic DNA is located in the nucleus and often tightly bound by histones, whereas mature mRNA is located in the cytoplasm. Moreover, RNA cannot integrate itself into the genome and is relatively unstable. This makes off-target edits less concerning than they would be in techniques that target DNA. Another advantage of site-directed RNA editing is that this procedure does not affect the level of mRNA expression. This is important because for many proteins, both under-expression and over-expression can lead to disorders. Lastly, there are numerous tools available for the manipulation of RNA because several enzymes are already known to be able to modify RNA in a base-specific manner. The ability to target and edit specific nucleosides has the potential to affect a myriad of genetic disorders beyond CF (12).
Future of Cystic Fibrosis In the 1950s, life expectancy for people with CF was approximately ten years. Now, the average life span is around 37 years due to extraordinary advances in medicine (CFF). Further research is currently being done on a variety of potential treatments. Earlier this year, Vertex Pharmaceuticals began to conduct Phase 3 clinical trials of the drugs Kalydeco and Lumacaftor. Another recent line of research seeks to apply stem cell therapy to CF, which is a “model disease” for this kind of research because the recurring lung inflammations cause frequent damage and remodeling, which could facilitate the engraftment of stem cells (13). Recently, researchers were able to induce stem cells isolated from umbilical cord blood to express phenotypic characteristics of lung epithelial cells in vitro, including expression of the CFTR protein. Although significant progress has been made in this endeavor, many challenges still remain. For instance, there is a wide range of phenotypes exhibited by various types of lung cells, so it may not be enough to get the cells to exhibit one specific phenotype (14). In addition, lung cells resulting from the differentiation of stem cells may not be chromosomally stable and could cause tumors (14). While clinical trials for stem cell therapy may not occur for a long time due to the WINTER 2014
Image courtesy of Wikimedia Commons. Available at http://upload.wikimedia.org/wikipedia/commons/4/4e/ClubbingCF.JPG
exploratory nature of this research (14), considering how far the field of cystic fibrosis research has progressed in just the past few decades, the future of this field seems very promising.
Figure 3: A common symptom of cystic fibrosis is digital clubbing, which involves noticeable bulging of the fingertip.
CONTACT YVETTE ZOU AT YVETTE.ZOU.16@DARTMOUTH.EDU References 1. Sangiuolo, Federica, et al. “Towards the Pharmacogenomics of Cystic Fibrosis.” Pharmacogenomics (2002). 2. “Overview of Epithelial Cells.” Davidson Biology. Web. 13 Dec. 2013. 3. “What Are the Signs and Symptoms of Cystic Fibrosis?” National Heart, Lung, and Blood Institute. Web. 13 Dec. 2013. <http://www.nhlbi.nih.gov/health/health-topics/topics/cf/ signs.html>. 4. “Cystic Fibrosis.” Genetics Home Reference. Web. 7 Dec. 2013. <http://ghr.nlm.nih.gov/condition/cystic-fibrosis>. 5. “Cystic Fibrosis.” Patient.co.uk. Web. 13 Dec. 2013. <http:// www.patient.co.uk/health/Cystic-Fibrosis.htm>. 6. Liu, Xuehong. “CFTR: What’s It Like Inside the Pore?” Journal of Experimental Zoology 300A (2003): 7. “Epithelial Transport.” University of Washington. Web. 13 Dec. 2013. 8. “Cystic Fibrosis: Case Study.” Genetic Science Learning Center. Web. 13 Dec. 2013. 9. Fischer, Horst. “Mechanism and Function of DUOX in Epithelia of the Lung.” Antioxidants & Redox Signaling (2009) 10. Pezzulo, Alejandro A. “Glucose Depletion in the Airway Surface Liquid Is Essential for Sterility of the Airways.” Public Library of Science. Web. 13 Dec. 2013. 11. Cystic Fibrosis Foundation. Web. 7 Dec. 2013. <http:// www.cff.org/>. 12. Montiel-Gonzalez, Maria Fernanda, and Isabel VallecilloViejo. “Correction of Mutations within the Cystic Fibrosis Transmembrane Conductance Regulator by Site-directed RNA Editing.” PNAS (2013): 13. Piro, Donatella. “Stem Cell Therapy for Cystic Fibrosis: Current Status and Future Prospects.” Expert Reviews Respiratory Medicine 2.3 (2008): 365-80. Print. 14. Moodley, Yuben. “Stem Cells: A Recapitulation of Development.” Respirology (2013): 29