One of the main causes of the aging process is the accumulation of damage produced by reactive oxygen species throughout life. While there are many ways to measure this damage, one widely used, flexible and sensitive metric is the Comet Assay. Briefly, in this assay a single-cell suspension of the cells or tissue under study are embedded in low melting point agarose on a microscope slide. The cells are lysed and placed in an alkaline buffer to unwind the supercoiled DNA. During electrophoresis, DNA-containing strand breaks migrate more quickly to form a Comet tail whereas undamaged DNA remains in the nucleus. The cells are then visualized by adding a DNA-specific stain and visualizing with confocal microscopy.
Data from the comet assay run on quail red blood cells are shown below. In the panels below, one cell shows very few single-strand DNA breaks, and so the DNA remains in the nucleus, or head of the comet (Panel A). In a cell from another individual, there was more oxidative damage to the DNA and so while unbroken DNA still remains in the comet head, damaged DNA is seen in comet tail (Panel B).
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