Chandlee, Joel, M.
Cell and Molecular Biology
genetics; epigenetics; gene regulation; development; behavior; cancer
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Genetics has taught us that genes are represented as discrete sequences within a larger DNA molecule found embedded within the chromosomes of a living cell. Collectively these chromosomes and their associated genes carry all of the instructions for life. Until recently, the prevailing thought has been that genes are destiny in the life of an individual since the genes carry the information that determines the general traits and characteristics associated with that individual. The relatively recent understanding of mechanisms that underlie epigenetic phenomena has led to a rethinking of this concept. Epigenetics describes cellular mechanisms that explain how two individuals with exactly identical genetic makeup can present significant differences with regard to their traits and characteristics. The source of these differences can be traced to specific epigenetic mechanisms that act to regulate activity of the underlying genes represented in the DNA of a chromosome. Epigenetic analyses have shown that factors besides the information encoded within the genes themselves have a role in how genes are expressed. The study of these mechanisms is known as ‘epigenetics’. Understanding epigenetic mechanisms has become of central importance in modern day genetics research. Epigenetics is the study of factors that affect gene expression, but does not alter the DNA sequence and subsequently have an affect in altering the expression of traits and characteristics of an individual. These altering factors have been demonstrated to be heritable through cell divisions and across generations as well, just like the genes themselves. Epigenetics introduces another level of complexity to our understanding of the regulation of gene expression and the need for future studies to better understand how genes are expressed. This paper attempts to explore the role of epigenetic mechanisms in disease, development, and behavior.
DNA methylation and histone modifications are two fundamental mechanisms by which gene expression can be altered through epigenetics. DNA methylation involves methyl group addition to the cytosine base in DNA. This addition to the DNA sequence has the ability to cause genes to alter patterns of expression. Lack of methylation at certain points in the DNA can be crippling to the individual and has been pinpointed as the basis of certain diseases including different forms of cancer. Histones are proteins that are used to package DNA into chromosomes. Several types of biochemical modifications to histones have been identified and shown to affect the degree to which the DNA molecule interacts with the histone proteins of the chromosome. Loosening and tightening of the DNA-histone interaction can cause genes to be expressed or silenced, respectively.
Strides in epigenetic studies have resulted in possible explanations for questions that could not have been answered previously through more traditional genetic studies. Epigenetic modifications have been implicated in a diverse array of situations making understanding pertinent for stem cell research, cancer research, and behavioral studies. The two common assays that the effects of epigenetic modifications have been assessed with have been chromatin immunoprecipitation (ChIP) and bisulfite sequencing. ChIP monitors the chromatin changes and bisulfite sequencing can track the pattern of DNA methylation.
Epigenetic modifications are also being examined on a whole genome level. The Human Epigenome Project is an international endeavor to sequence the epigenetic changes in the human genome that occur during development and between tissue types. The significance of the outcomes of the Epigenome Project and the role epigenetic mechanisms play in various biological phenomena will be explored in this research paper through a review of the current literature.