Examination of Global Methylation and Targeted Imprinted Genes in Prader-Willi Syndrome

Retrotransposons and Diabetes Mellitus

Retrotransposons are invasive genetic elements, which replicate by copying and pasting themselves throughout the genome in a process called retrotransposition. The most abundant retrotransposons by number in the human genome are Alu and LINE-1 elements, which comprise approximately 40% of the human genome. The ability of retrotransposons to expand and colonize eukaryotic genomes has rendered them evolutionarily successful and is responsible for creating genetic alterations leading to significant impacts on their hosts. Previous research suggested that hypomethylation of Alu and LINE-1 elements is associated with global hypomethylation and genomic instability in several types of cancer and diseases, such as neurodegenerative diseases, obesity, osteoporosis, and diabetes mellitus (DM). With the advancement of sequencing technologies and computational tools, the study of the retrotransposon's association with physiology and diseases is becoming a hot topic among researchers. Quantifying Alu and LINE-1 methylation is thought to serve as a surrogate measurement of global DNA methylation level. Although Alu and LINE-1 hypomethylation appears to serve as a cellular senescence biomarker promoting genomic instability, there is sparse information available regarding their potential functional and biological significance in DM. This review article summarizes the current knowledge on the involvement of the main epigenetic alterations in the methylation status of Alu and LINE-1 retrotransposons and their potential role as epigenetic markers of global DNA methylation in the pathogenesis of DM.

Pyrosequencing Methylation Analysis

Pyrosequencing, a real-time sequencing technology, is considered a "gold standard" for quantitative allele quantification at single base resolution. Quantitative bisulfite Pyrosequencing determines DNA methylation level by analyzing artificial "C/T" SNPs at CpG sites within a specific Pyrosequencing assay. The bisulfite Pyrosequencing methylation assay design is DNA strand specific and the primer design should not contain any CpG sites and should be free of high-frequency mutations. Additionally Pyrosequencing assays must be tested for preferential amplification during bisulfite PCR to ensure the sequencing quantification accuracy and reproducibility. Pyrosequencing analysis gives a reproducible measurement of average methylation at several CpG sites within the Pyrosequencing assay directly from a PCR product, rapidly and accurately for many samples at a time. It is therefore well suited for clinical research, validation of whole-genome methylation screening results, and global methylation analysis using repetitive elements including LINE-1, Alu, and Sat2. Pyrosequencing reproducibility and accuracy result in low measurement variance, thereby increasing the likelihood of early detection of small changes in methylation levels that may become apparent in response to treatment. For example, the high reproducibility of the LINE-1 assay is important for detecting the relatively small daily changes in methylation levels associated with hypomethylation. This enables detection of differences in patterns between normal and disease tissue such as in tumor suppresser genes, and to determine global methylation changes in response drug treatments. Relatively low cost and easy automation allows the researcher to increase the experiment's sample population to detect trends that would otherwise not have a sufficient sampling basis for statistical significance.