Figure 2. DNA methylation profiles in the proximal promoter region. (A) A detailed map of CpG sites in the region. The short vertical lines indicate the locations of CpG sites, and the numbers below them show the exact location in the COL1A1 map. The transcription start site is +1. (B) Methylation of cytosine at CpG sites in human periodontal ligament samples from donors of 8 different ages. The numbers at the left side of the arrays of circles show the DNA clone number. Open circles show no methylation, and the closed circles indicate methylated cytosine. Each circle represents the CpG site shown in (A), in the same order. The DNA clones from the periodontal ligaments of older people show a high incidence of methylated cytosines. (C) The degree of methylation at each CpG site was calculated as a percentage of the methylated cytosines seen in all clones for each sample. The averages of the frequencies of methylation at each CpG site in four younger and four older humans were calculated with their standard deviations. Open columns represent younger humans, and the closed columns, older humans. The bars on each column show standard deviations. Asterisks above the bars show that the levels of methylation are different between younger and older tissues at a statistically significant level, p < 0.05.