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Methylation: Addition of methyl groups. In histo-chemistry methylation is used to esterify carboxyl groups and remove sulfate groups by treating tissue sections with hot methanol in the presence of hydrochloric acid. (From Stedman, 25th ed)

DNA Methylation Analysis

JoVE 5550

Methylation at CpG dinucleotides is a chemical modification of DNA hypothesized to play important roles in regulating gene expression. In particular, the methylation of clusters of methylation sites, called “CpG islands”, near promoters and other gene regulatory elements may contribute to the stable silencing of genes, for example, during epigenetic processes…


Enhanced Reduced Representation Bisulfite Sequencing for Assessment of DNA Methylation at Base Pair Resolution

1Department of Medicine, Weill Cornell Medical College, 2Institute for Computational Biomedicine, Weill Cornell Medical College, 3Department of Physiology and Biophysics, Weill Cornell Medical College, 4Department of Pathology, University of Michigan

JoVE 52246


Epigenetic Regulation

JoVE 10803

Epigenetic mechanisms play an essential role in healthy development. Conversely, precisely regulated epigenetic mechanisms are disrupted in diseases like cancer.

In most mammals, females have two X chromosomes (XX) while males have an X and a Y chromosome (XY). The X chromosome contains significantly more genes than the Y chromosome. Therefore, to prevent an excess of X chromosome-linked gene expression in females, one of the two X chromosomes is randomly silenced during early development. This process, called X-chromosome inactivation, is regulated by DNA methylation. Scientists have found greater DNA methylation at gene promoter sites on the inactive X chromosome than its active counterpart. DNA methylation prevents the transcription machinery from attaching to the promoter region, thus inhibiting gene transcription. Abnormal DNA methylation plays an important role in cancer. The promoter region of most genes contains stretches of cytosine and guanine nucleotides linked by a phosphate group. These regions are called CpG islands. In healthy cells, CpG islands are not methylated. However, in cancer cells, CpG islands in the promoter regions of tumor suppressor genes or cell cycle regulators are excessively methylated. Methylation turns off the expression of these genes, allowing cancer cells to divide rapidly and uncontrollably.

 Core: Biology

RNA Stability

JoVE 11009

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations between RNA and DNA underlie the differences in their stability and longevity. Because DNA is double-stranded, it is inherently more stable. The single-stranded structure of RNA is less stable but also more flexible and can form weak internal bonds. Additionally, most RNAs in the cell are relatively short, while DNA can be up to 250 million nucleotides long. RNA has a hydroxyl group on the second carbon of the ribose sugar, increasing the likelihood of breakage of the sugar-phosphate backbone. The cell can exploit the instability of RNA, regulating both its longevity and availability. More stable mRNAs will be available for translation for a longer period of time than less stable mRNAs transcripts. RNA binding proteins (RBPs) in cells play a key role in the regulation of RNA stability. RBPs can bind to a specific sequence (AUUUA) in the 3’ untranslated region (UTR) of mRNAs. Interestingly, the number of AUUUA repeats appears to recruit RBPs in a specific way: fewer repeats recruit stabilizing RBPs. Several, overlapping repeats result in the binding of destabilizing RBPs. All cells have enzymes called RNases that break down RNAs. Typically, the 5’cap and polyA tail protect eukaryotic mRNA from degradation

 Core: Biology

An Overview of bGDGT Biomarker Analysis for Paleoclimatology

JoVE 10256

Source: Laboratory of Jeff Salacup - University of Massachusetts Amherst

Throughout this series of videos, natural samples were extracted and purified in search of organic compounds, called biomarkers, that can relate information on climates and environments of the past. One of the samples analyzed was sediment. Sediments accumulate…

 Earth Science
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