Illustration of tissue-specific and gestational age-specific methylation at the proximal promoter regions of GNAS and CDKN1C. (A) and (E) Schematics showing the positions of the Illumina Infinium probes relative to the genes and transcripts. Arrow directions represent the transcriptional directions for the genes or transcripts. Genomic coordinates were retrieved from the UCSC Genome Brower database (hg18). (B) through (D) Average methylation levels of the Illumina Infinium probes in different placental groups (top) and in different tissues (bottom). Probe numbers are shown on the x-axes in the bottom panels divided into (B) GNAS region 1, (C) GNAS region 2 and (D) GNAS region 3 according to their proximity to the known transcripts. Tissue-specific methylation can be found from cg15160445 to cg16833551 in GNAS region 2 and at cg01565918 in GNAS region 3. (F) through (H) Average methylation levels of the Illumina Infinium probes of CDKN1C in (F) different placental groups, (G) different gestational ages of placenta and (H) different tissues. Probe numbers are shown on the x-axes. Both tissue-specific and gestational age-specific methylation can be found at cg20919799. PLN(E): early gestation placenta; PLN(M): midgestation placenta; PLN(T): term placenta; MUS: muscle; BRN: brain; KID: kidney; WB: whole blood.