A novel method for detecting 7-methyl guanine reveals aberrant methylation levels in Huntington disease

Guanine methylation is a ubiquitous process affecting DNA and various RNA species. N-7 guanine methylation (7-MG), although relatively less studied, could have a significant role in normal transcriptional regulation as well as in the onset and development of pathological conditions. The lack of a sensitive method to accurately quantify trace amounts of altered bases such as 7-MG has been a major deterrent in delineating its biological function(s). Here we report the development of methods to detect trace amounts of 7-MG in biological samples using electrochemical detection combined with high-performance liquid chromatography (HPLC) separation of compounds. We further sought to assess global alterations in DNA methylation in Huntington disease (HD), where transcriptional dysregulation is a major factor in pathogenesis. The developed method was used to study guanine methylation in cytoplasmic and nuclear nucleic acids from human and transgenic mouse HD brain and controls. Significant differences were observed in the guanine methylation levels in mouse and human samples, consistent with the known transcriptional pathology of HD. The sensitivity of the method makes it capable of detecting subtle aberrations. Identification of changes in methylation pattern will provide insights into the molecular mechanism changes that translate into onset and/or development of symptoms in diseases such as HD.