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| Briefing: Epigenetics and Epigenomics |
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| SciMed - Genetics & Genome | |||
| TS-Si News Service | |||
| Friday, 29 May 2009 10:20 | |||
 Springfield, VA, USA. From its beginnings, traditional genetics had attributed human characteristics to a simple arithmetical combination of inheritable traits from unchanging genes. As a result, genetic mutations and recombinations have driven most descriptions of how traits are handed down from one generation to another, with misleading effects on a confused public.
The discovery and understanding of DNA, and the role of non-coding (junk) DNA, reveals a more complex — and subtle — situation. Today, scientists know that heritable changes in gene function can occur without a change in the DNA sequence.
Called epigenetics, this insight has further changed the way researchers think about heredity. Epigenetics bridges the gap between nature and nurture.
Both epigenetics and epigenomics — the genomewide distribution of epigenetic changes — are related to many other topics requiring a thorough understanding of all aspects of genetics. The latter includes aging, agriculture, cloning, evolution, sexual differentiation, species conservation, stem cells, and synthetic biology.
Proteins
Proteins perform many of the essential functions in the human body. When a protein, or a group of proteins, fail to act in their normal way, we get sick. Most medicines exploit this by binding to proteins and influencing their activity. Researchers can design drugs with molecules that fit if they know the shape of a protein "target".
So, when DNA is copied from cell to cell, it is essential that the epigenetic code is also copied accurately. If not, a liver cell may divide into another type of cell, such as a nerve or eye cell. A breakdown in this system might also mean that a gene for cell growth is accidentally switched on, for example, leading to unregulated cell growth and the development of tumors.
Research into protein structure has accelerated with improved methods, computers, and access to the complete sequence of our DNA (the human genome). The field of structural genomics is focused on the three-dimensional structures of proteins. The information on structure provides a powerful means to develop a diagram of a protein suitable for further research and implementation in new treatment methods.
Epigenetic Regulation
There are more than 200 different cell types in the human body; each cell contains the same genetic information and can, in theory, synthesize the same proteins. However, each cell type is unique and synthesizes a specific set of proteins. Nerve cells synthesize proteins that are necessary for generating nerve cells, muscle cells synthesize those necessary for building muscle fibers, etc.
This specialization takes place during early embryonic development and continues throughout a person's life. Cells exercise control over their own development using a mechanism called epigenetic regulation, which “opens” or "closes" the DNA structure. Differences in protein synthesis result from the activation and inactivation of genes.
This is fundamental to all animals, humans, and plants (eukaryotic cells). It is involved in tissue regeneration and the preservation of stem cells and DNA.
Epigenetic processes are natural and essential to many organism functions, but disruptions can result in major adverse health and behavioral effects. Variations in epigenetic gene activity regulation are causally connected in human beings to disruptions in early embryonic development and serious diseases.
The cell has to condense two meters of DNA inside a 1/100 millimeter diameter body. During the condensation process, the cell mechanism determines which genes activate. A special group of proteins, called the histones, plays a central part during this process.
The DNA is wound around the histones — which also determine the DNA structure — during condensation. They attach a number of complex and relatively unknown combinations of small chemical modifications under the influence of different enzymes. This opens and closes parts of the DNA structure to regulate gene activation — specific for each of our distinct cell types.
Gene Imprinting
Imprinted genes don't rely on the traditional laws of Mendelian genetics, which describe the inheritance of traits as either dominant or recessive. In Mendelian genetics, both parental copies are equally likely to contribute to the outcome. The impact of an imprinted gene copy, however, depends only on which parent it was inherited from. For some imprinted genes, the cell only uses the copy from the mother to make proteins, and for others only that from the father.
In the mid 1980s, scientists studying mice discovered that normal development requires the inheritance of genetic material from both a male and a female. The resulting variances changed, depending on the material's origin.
One hypothesis has it that imprinting regulates embryonic growth. Maternally-expressed imprinted genes usually suppress growth, while those from the male parent usually enhance growth, ensuring continuation of the father's genes.
This is important for a species in which a single litter of offspring can result from the contributions of more than one male. However, the mother, interested in her own health maintenance (biologically speaking), "fights" the paternal genes and limits the size of the embryo or fetus.
NoteThis article is an update of an earlier version published under the same title.
 The TS-Si News Service is a collaborative effort by TS-Si.org editors, contributors, and corresponding institutions. The sources can include the cited individuals and organizations, as well as TS-Si.org staff contributions. Articles and news reports do not necessarily convey official positions of TS-Si, its partners, or affiliates. We welcome your comments. Use the form below to leave a public comment or send private correspondence via the TS-Si Contact Page. We will not divulge any personal details or place you on a mailing list without your permission.                      Add this page to your favorite Social Bookmarking websites.
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| Last Updated on Friday, 29 May 2009 10:23 |
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The TS-Si News Service is a collaboration of TS-Si staff, contributors, and corresponding institutions. Contents do not necessarily convey official positions of TS-Si, its partners, or affiliates