Bio-COBRA: absolute quantification of DNA methylation in electrofluidics chips

Microfluidic platforms for DNA methylation analysis

In the field of genetics, epigenetics is the study of changes in gene expression without any change in DNA sequences. Chemical base modification in DNA by DNA methyltransferase, and specifically methylation, has been well studied as the main mechanism of epigenetics. Therefore, the determination of DNA methylation of, for example, 5'-methylcytosine in the CpG sequence in mammals has attracted attention because it should prove valuable in a wide range of research fields including diagnosis, drug discovery, and therapy. Methylated DNA bases and DNA methyltransferase activity are analyzed using conventional methods; however, these methods are time-consuming and require complex multiple operations. Therefore, new methods and devices for DNA methylation analysis are now being actively developed. Furthermore, microfluidic technology has also been applied to DNA methylation analysis because the microfluidic platform offers the promising advantage of making it possible to perform thousands of DNA methylation reactions in small reaction volumes, resulting in a high-throughput analysis with high sensitivity. This review discusses epigenetics and the microfluidic platforms developed for DNA methylation analysis.

Meeting the methodological challenges in molecular mapping of the embryonic epigenome

The past decade of life sciences research has been driven by progress in genomics. Many voices are already proclaiming the post-genomics era, in which phenomena other than sequence polymorphism influence gene expression and also explain complex phenotypes. One of these burgeoning fields is the study of the epigenome. Although the mechanisms by which chromatin structure and reorganization as well as cytosine methylation influence gene expression are not fully understood, they are being invoked to explain the now-accepted long-term impact of the environment on gene expression, which appears to be a factor in the development of numerous diseases. Such studies are particularly relevant in early embryonic development, during which waves of epigenetic reprogramming are known to have profound impacts. Since gametes and zygotes are in the process of resetting the genome in order to create embryonic stem cells that will each differentiate to create one of many specific tissue types, this phase of life is now viewed as a window of susceptibility to epigenetic reprogramming errors. Epigenetics could explain the influence of factors such as the nutritional/metabolic status of the mother or the artificial environment of assisted reproductive technologies. However, the peculiar nature of early embryos in addition to their scarcity poses numerous technological challenges that are slowly being overcome. The principal subject of this article is to review the suitability of various current and emerging technological platforms to study oocytes and early embryonic epigenome with more emphasis on studying DNA methylation. Furthermore, the constraint of samples size, inherent to the study of preimplantation embryo development, was put in perspective with the various molecular platforms described.

Deciphering the epigenetic code: an overview of DNA methylation analysis methods

SIGNIFICANCE

Methylation of cytosine in DNA is linked with gene regulation, and this has profound implications in development, normal biology, and disease conditions in many eukaryotic organisms. A wide range of methods and approaches exist for its identification, quantification, and mapping within the genome. While the earliest approaches were nonspecific and were at best useful for quantification of total methylated cytosines in the chunk of DNA, this field has seen considerable progress and development over the past decades.

RECENT ADVANCES

Methods for DNA methylation analysis differ in their coverage and sensitivity, and the method of choice depends on the intended application and desired level of information. Potential results include global methyl cytosine content, degree of methylation at specific loci, or genome-wide methylation maps. Introduction of more advanced approaches to DNA methylation analysis, such as microarray platforms and massively parallel sequencing, has brought us closer to unveiling the whole methylome.

CRITICAL ISSUES

Sensitive quantification of DNA methylation from degraded and minute quantities of DNA and high-throughput DNA methylation mapping of single cells still remain a challenge.

FUTURE DIRECTIONS

Developments in DNA sequencing technologies as well as the methods for identification and mapping of 5-hydroxymethylcytosine are expected to augment our current understanding of epigenomics. Here we present an overview of methodologies available for DNA methylation analysis with special focus on recent developments in genome-wide and high-throughput methods. While the application focus relates to cancer research, the methods are equally relevant to broader issues of epigenetics and redox science in this special forum.

DNA methylation analysis in human cancer

The functional impact of aberrant DNA methylation and the widespread alterations in DNA methylation in cancer development have led to the development of a variety of methods to characterize the DNA methylation patterns. This chapter critiques and describes the major approaches to analyzing DNA methylation.

DNA methylation and cancer diagnosis: new methods and applications

Methylation of cytosines in cytosine-guanine (CpG) dinucleotides is one of the most important epigenetic alterations in animals. The presence of methylcytosine in the promoter of specific genes has profound consequences on local chromatin structure and on the regulation of gene expression. Changes in DNA methylation play a central role in carcinogenesis. Hypermethylation and consecutive transcriptional silencing of tumor-suppressor genes has been documented in numerous cancers. The identification of target genes silenced by this modification has a great impact on diagnosis, classification, definition of risk groups and prognosis of cancer patients. Here we outline genome-wide techniques aiming at the identification of relevant methylated promoters. Methods and applications allowing clinicians to monitor the methylation of target genes will be also reviewed.