Genomic and mitochondrial DNA bases undergo continuous modifications as a result of both natural processes that introduce epigenetic markers as well as exposure to DNA damaging agents through oxidation and alkylation reactions from endogenous sources or toxicants. DNA sequencing techniques do not directly detect DNA damage because the sequencing takes place on PCR-amplified strands that perforce contain only the 4 canonical bases A, C, T, and G. Mutations can be detected by sequencing, and many of these are the ultimate outcome of DNA damage. However, mutations themselves do not provide much information about the chemical identity of the original damage. This project will examine an approach to detection of DNA base modification (e.g. oxidation, alkylation, or excision) by application of chemical and enzymatic methods to convert the modified base to an adduct that yields a detectable signal when individual DNA strands translocate through a membrane-embedded ion channel. This method will provide a direct read-out of DNA damage on single molecules The long-term goal is to develop methodology compatible with microfluidics to analyze very small samples of DNA from cellular sources.
The specific aims of this project are to (1) optimize the conversion of specific DNA lesions to adducts detectable by the nanopore ion channel method by a combination of organic and enzymatic chemistries, (2) optimize the ion channel measurements to detect and quantify single-site DNA damage and demonstrate that DNA strand carrying adducts are translocated through the pore, (3) validate the methods using large DNA targets such as the plasmid M13mp18 after chemical damage, and (4) develop a method to PCR amplify DNA damage by generation of a specific 5th dNTP for enzymatic demarcation of damage sites. Realization of the long-term goals of this project will impact research in human health in 3 areas: (1) personalized drug therapy, (2) early detection of disease, and (3) epigenetics.
The ability to monitor specific DNA base damage sites in tissue samples would have a significant impact on human health by rapid evaluation of genetic damage caused by cancer treatments or environmental toxins. In addition, the ability to detect DNA damage occurring in specific genes may guide physicians to preventative care. The methods developed in this research may also provide epigenetic tools for linking DNA modification to disease states.
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