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Epigenomics
Epigenomics is the study of the complete set of epigenetic modifications on the genetic material of a cell, known as the epigenome. The field is analogous to genomics and proteomics, which are the study of the genome and proteome of a cell (Russell 2010 p. 217 & 230). Epigenetic modifications are reversible modifications on a cell’s DNA or histones that affect gene expression without altering the DNA sequence (Russell 2010 p. 475). Two of the most characterized epigenetic modifications are DNA methylation and histone modification. Epigenetic modifications play an important role in gene expression and regulation, and are involved in numerous cellular processes such as in differentiation/development and tumorigenesis (Russell 2010 p. 597). The study of epigenetics on a global level has been made possible only recently through the adaptation of genomic high-throughput assays (Laird 2010) and.〔
==Introduction to Epigenetics==
The mechanisms governing phenotypic plasticity, or the capacity of a cell to change its state in response to stimuli, have long been the subject of research (Phenotypic plasticity 1). The traditional central dogma of biology states that the DNA of a cell is transcribed to RNA, which is translated to proteins, which perform cellular processes and functions (Crick 1970). A paradox exists, however, in that cells exhibit diverse responses to varying stimuli and that cells sharing identical sets of DNA such as in multicellular organisms can have a variety of distinct functions and phenotypes (Bird 2002). Classical views have attributed phenotypic variation to differences in primary DNA structure, be it through aberrant mutation or an inherited sequence allele (Johannes 2008). However, while this did explain some aspects of variation, it does not explain how tightly coordinated and regulated cellular responses, such as differentiation, are carried out.
A more likely source of cellular plasticity is through the Regulation of gene expression, such that while two cells may have near identical DNA, the differential expression of certain genes results in variation. Research has shown that cells are capable of regulating gene expression at several stages: mRNA transcription, processing and transportation as well as in protein translation, post-translational processing and degradation. Regulatory proteins that bind to DNA, RNA, and/or proteins are key effectors in these processes and function by positively or negatively regulating specific protein level and function in a cell (Russell 2010 p 518-19). And, while DNA binding transcription factors provide a mechanism for specific control of cellular responses, a model where DNA binding transcription factors are the sole regulators of gene activity is also unlikely. For example, in a study of Somatic-cell nuclear transfer, it was demonstrated that stable features of differentiation remain after the nucleus is transferred to a new cellular environment, suggesting that a stable and heritable mechanism of gene regulation was involved in the maintenance of the differentiated state in the absence of the DNA binding transcription factors (Bird 2002).
With the finding that DNA methylation and histone modifications are stable, heritable, and also reversible processes that influence gene expression without altering DNA primary structure, a mechanism for the observed variability in cell gene expression was provided (Johannes 2008). These modifications were termed epigenetic, from epi “on top of” the genetic material “DNA” (Epigenetics 1). The mechanisms governing epigenetic modifications are complex, but through the advent of high-throughput sequencing technology they are now becoming better understood (Johannes 2008).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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