OTHER CHEMICAL APPROACHES
Great progress has been made in neurobiology through the application of chemistry to reveal the molecular basis for behavior and the properties of the genome. Chemical treatments have been indispensable for the detection of changes on DNA, particularly for detection of rare DNA modifications (such as 5fC and 5caC) at single-base resolution.
Although bisulfite treatment remains the most widely used chemical treatment to detect modified DNA bases, other approaches have been characterized and many are able to detect modifications to bases other than 5mC and 5hmC. Lu et al. (2013) first demonstrated chemical labeling to detect 5caC. Then, Hardisty, Kawasaki, Sahakyan, and Balasubramanian (2015) successfully used a selective chemical labeling to study modified uracil bases (5-hydroxymethyluracil and 5-formyluracil) in the genome. A Chinese group discovered that treatment of DNA that with hot piperidine could produce a specific cleavage at the position of 5fC, providing a convenient method to selectively detect 5fC (Mao et al., 2013); it is similar to restriction enzyme-based methods, but has no sequence bias. Other groups have developed alternative methods to assay 5fC; Xia et al. (2015) invented a bisulfite-free method for whole-genome analysis of 5fC based on selective chemical labeling of 5fC and subsequent C-to-T transition during PCR, which could obtain genome-wide maps of 5fC at single-base resolution.