Category Archives: Epigenetics

Epigenetics, the study of the chemical modification of specific genes or gene-associated proteins of an organism. Epigenetic modifications can define how the information in genes is expressed and used by cells. The term epigenetics came into general use in the early 1940s, when British embryologist Conrad Waddington used it to describe the interactions between genes and gene products, which direct development and give rise to an organisms phenotype (observable characteristics). Since then, information revealed by epigenetics studies has revolutionized the fields of genetics and developmental biology. Specifically, researchers have uncovered a range of possible chemical modifications to deoxyribonucleic acid (DNA) and to proteins called histones that associate tightly with DNA in the nucleus. These modifications can determine when or even if a given gene is expressed in a cell or organism.

The principal type of epigenetic modification that is understood is methylation (addition of a methyl group). Methylation can be transient and can change rapidly during the life span of a cell or organism, or it can be essentially permanent once set early in the development of the embryo. Other largely permanent chemical modifications also play a role; these include histone acetylation (addition of an acetyl group), ubiquitination (the addition of a ubiquitin protein), and phosphorylation (the addition of a phosphoryl group). The specific location of a given chemical modification can also be important. For example, certain histone modifications distinguish actively expressed regions of the genome from regions that are not highly expressed. These modifications may correlate with chromosome banding patterns generated by staining procedures common in karyotype analyses. Similarly, specific histone modifications may distinguish actively expressed genes from genes that are poised for expression or genes that are repressed in different kinds of cells.

It is clear that at least some epigenetic modifications are heritable, passed from parents to offspring in a phenomenon that is generally referred to as epigenetic inheritance, or passed down through multiple generations via transgenerational epigenetic inheritance. The mechanism by which epigenetic information is inherited is unclear; however, it is known that this information, because it is not captured in the DNA sequence, is not passed on by the same mechanism as that used for typical genetic information. Typical genetic information is encoded in the sequences of nucleotides that make up the DNA; this information is therefore passed from generation to generation as faithfully as the DNA replication process is accurate. Many epigenetic modifications, in fact, are spontaneously erased or reset when cells reproduce (whether by meiosis or mitosis), thereby precluding their inheritance.

Epigenetic changes not only influence the expression of genes in plants and animals but also enable the differentiation of pluripotent stem cells (cells having the potential to become any of many different kinds of cells). In other words, epigenetic changes allow cells that all share the same DNA and are ultimately derived from one fertilized egg to become specializedfor example, as liver cells, brain cells, or skin cells.

As the mechanisms of epigenetics have become better understood, researchers have recognized that the epigenomechemical modification at the level of the genomealso influences a wide range of biomedical conditions. This new perception has opened the door to a deeper understanding of normal and abnormal biological processes and has offered the possibility of novel interventions that might prevent or ameliorate certain diseases.

Epigenetic contributions to disease fall into two classes. One class involves genes that are themselves regulated epigenetically, such as the imprinted (parent-specific) genes associated with Angelman syndrome or Prader-Willi syndrome. Clinical outcomes in cases of these syndromes depend on the degree to which an inherited normal or mutated gene is or is not expressed. The other class involves genes whose products participate in the epigenetic machinery and thereby regulate the expression of other genes. For example, the gene MECP2 (methyl CpG binding protein 2) encodes a protein that binds to specific methylated regions of DNA and contributes to the silencing of those sequences. Mutations that impair the MECP2 gene can lead to Rett syndrome.

Many tumours and cancers are believed to involve epigenetic changes attributable to environmental factors. These changes include a general decrease in methylation, which is thought to contribute to the increased expression of growth-promoting genes, punctuated by gene-specific increases in methylation that are thought to silence tumour-suppressor genes. Epigenetic signaling attributed to environmental factors has also been associated with some characteristics of aging by researchers that studied the apparently unequal aging rates in genetically identical twins.

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One of the most promising areas of epigenetic investigation involves stem cells. Researchers have understood for some time that epigenetic mechanisms play a key role in defining the potentiality of stem cells. As those mechanisms become clearer, it may become possible to intervene and effectively alter the developmental state and even the tissue type of given cells. The implications of this work for future clinical regenerative intervention for conditions ranging from trauma to neurodegenerative disease are profound.

...and the yeast Saccharomyces cerevisiae, as well as for numerous microorganisms. Additional research during this time explored alternative mechanisms of inheritance, including epigenetic modification (the chemical modification of specific genes or gene-associated proteins), that could explain an organisms ability to transmit traits developed during its lifetime to its...

The term epigenetic is used to describe the dynamic interplay between genes and the environment during the course of development. The study of epigenetics highlights the complex nature of the relationship between the organisms genetic code, or genome, and the organisms directly observable physical and psychological manifestations and behaviours. In contemporary use, the term refers to...

unit of hereditary information that occupies a fixed position (locus) on a chromosome. Genes achieve their effects by directing the synthesis of proteins.

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Epigenetics

PBS air date: July 24, 2007

CHEERFUL NEIL DEGRASSE TYSON: Did you ever notice that if you get to know two identical twins, they might look alike, but they're always subtly different?

CANTANKEROUS NEIL DEGRASSE TYSON: Yep, whatever.

CHEERFUL NEIL DEGRASSE TYSON: As they get older, those differences can get more pronounced. Two people start out the same but their appearance and their health can diverge. For instance, you have more gray hair.

CANTANKEROUS NEIL DEGRASSE TYSON: No. No, I don't. Identical twins have the same DNA, exact same genes.

CHEERFUL NEIL DEGRASSE TYSON: Yeah.

CANTANKEROUS NEIL DEGRASSE TYSON: And don't our genes make us who we are?

CHEERFUL NEIL DEGRASSE TYSON: Well they do, yes, but they're not the whole story. Some researchers have discovered a new bit of biology that can work with our genes or against them.

CANTANKEROUS NEIL DEGRASSE TYSON: Yeah, you're heavier, and I'm better looking.

CHEERFUL NEIL DEGRASSE TYSON: Yeah, whatever.

NEIL DEGRASSE TYSON: Imagine coming into the world with a person so like yourself, that for a time you don't understand mirrors.

CONCEPCIN: As a child, when I looked in the mirror I'd say, "That's my sister." And my mother would say, "No, that's your reflection!"

NEIL DEGRASSE TYSON: And even if you resist this cookie-cutter existence, cultivate individual styles and abilitieslike cutting your hair differently, or running fasteruncanny similarities bond you together: facial expressions, body language, the way you laughor dress for an interview, perhaps, when you hadn't a clue what your sister was going to wear. The synchrony in your lives constantly confronts you.

CLOTILDE: When I see my sister, I see myself. If she looks good, I think, "I look pretty today." But if she's not wearing makeup, I say, "My god, I look horrible!"

NEIL DEGRASSE TYSON: It's hardly surprising because you both come from the same egg. You have precisely the same genes. And you are literally clones, better known, as identical twins.

But now, imagine this: one day, your twin, your clone, is diagnosed with cancer. If you're the other twin, what can you do except wait for the symptoms?

CLOTILDE: I have been told that I am a high risk for cancer. Damocles' sword hangs over me.

NEIL DEGRASSE TYSON: And yet, it's not uncommon for a twin, like Ana Mari, to get a dread disease, while the other, like Clotilde, doesn't. But how can two people so alike, be so unalike?

Well, these mice may hold a clue. Their DNA is as identical as Ana Mari and Clotilde's despite the differences in their color and size. The human who studies them is Duke University's Randy Jirtle.

So, Randy, I see here you have skinny mice and fat mice. What have you done in this lab?

RANDY JIRTLE: Well, these animals are actually genetically identical.

NEIL DEGRASSE TYSON: The fat ones and the skinny ones?

RANDY JIRTLE: That's correct.

NEIL DEGRASSE TYSON: Because these are huge.

RANDY JIRTLE: They're huge.

NEIL DEGRASSE TYSON: Can we weigh them and find out?

RANDY JIRTLE: Sure. So if you take this...

NEIL DEGRASSE TYSON: It looks like they can barely walk.

RANDY JIRTLE: They can't walk too much. They're not going to be running very far. So that's about 63 grams.

NEIL DEGRASSE TYSON: 63 grams.

RANDY JIRTLE: Let's look at the other one.

NEIL DEGRASSE TYSON: So it's half the weight.

RANDY JIRTLE: Right.

NEIL DEGRASSE TYSON: This gets even more mysterious when you realize that these identical mice both have a particular gene, called agouti, but in the yellow mouse it stays on all the time, causing obesity.

Just look at this.

So what accounts for the thin mouse? Exercise? Atkins? No, a tiny chemical tag of carbon and hydrogen, called a methyl group, has affixed to the agouti gene, shutting it down. Living creatures possess millions of tags like these. Some, like methyl groups, attach to genes directly, inhibiting their function. Other types grab the proteins, called histones, around which genes coil, and tighten or loosen them to control gene expression. Distinct methylation and histone patterns exist in every cell, constituting a sort of second genome, the epigenome.

RANDY JIRTLE: Epigenetics literally translates into just meaning "above the genome." So if you would think, for example, of the genome as being like a computer, the hardware of a computer, the epigenome would be like the software that tells the computer when to work, how to work, and how much.

NEIL DEGRASSE TYSON: In fact, it's the epigenome that tells our cells what sort of cells they should be. Skin? Hair? Heart? You see, all these cells have the same genes. But their epigenomes silence the unneeded ones to make cells different from one another. Epigenetic instructions pass on as cells divide, but they're not necessarily permanent. Researchers think they can change, especially during critical periods like puberty or pregnancy.

Jirtle's mice reveal how the epigenome can be altered. To produce thin, brown mice instead of fat, yellow ones, he feeds pregnant mothers a diet rich in methyl groups to form the tags that can turn genes off.

RANDY JIRTLE: And I think you can see that we dramatically shifted the coat color and we get many, many more brown animals.

NEIL DEGRASSE TYSON: And that matters because your coat color is a tracer, is an indicator...

RANDY JIRTLE: That's correct.

NEIL DEGRASSE TYSON: ...of the fact that you have turned off that gene?

RANDY JIRTLE: That's right.

NEIL DEGRASSE TYSON: This epigenetic fix was also inherited by the next generation of mice, regardless of what their mothers ate. And when an environmental toxin was added to the diet instead of nutrients, more yellow babies were born, doomed to grow fat and sick like their mothers.

It seems to me, this has profound implications for our health.

RANDY JIRTLE: It does, for human health. If there are genes like this in humans, basically, what you eat can affect your future generations. So you're not only what you eat, but potentially what your mother ate, and possibly even what your grandparents ate.

NEIL DEGRASSE TYSON: So how do you go to humans to do this experiment, when you have these mice, and they're genetically identical on purpose?

RANDY JIRTLE: That's right.

NEIL DEGRASSE TYSON: So, who is your perfect lab human?

RANDY JIRTLE: Well, then we look for identical humans, which are identical twins.

NEIL DEGRASSE TYSON: Twins, twins.

And that brings us to the reason why we're showing you Spanish twins. In 2005, they participated in a groundbreaking study in Madrid. Its aim? To show just how identical, epigenetically, they are or aren't.

MANEL ESTELLER (Spanish National Cancer Center): One of the questions of twins is, "If my twin has this disease, I will have the same disease?" And genetics tell us that there is a high risk of developing the same disease. But it's not really sure they are going to have it, because our genes are just part of the story. Something has to regulate these genes, and part of the explanation is epigenetics.

NEIL DEGRASSE TYSON: Esteller wanted to see if the twins' epigenomes might account for their differences. To find out, he and his team collected cells from 40 pairs of identical twins, age three to 74, then began the laborious process of dissolving the cells until all that was left were wispy strands of DNA, the master molecule that contains our genes.

Next, researchers amplified fragments of the DNA, until the genes themselves became detectable. Those that had been turned off epigenetically appear as dark pink bands on the gel. Now, notice what happens when the genes from a pair of twins are cut out and overlapped.

The results are far from subtle, especially when you compare the epigenomes of two sets of twins that differ in age. Here, on the left, is the overlapped DNA of six-year-old Javier and Carlos. The yellow indicates where their gene expression is identical.

On the right, is the DNA of 66-year-old Ana Mari and Clotilde. In contrast to the younger twins, hardly any yellow shines through. Their epigenomes have changed dramatically.

The study suggests that, as twins age, epigenetic differences accumulate, especially when their lifestyles differ.

MANEL ESTELLER: One of the main findings of our research is that epigenomes can change in function of what we eat, of what we smoke, of what we drink. And this is one of the key differences between epigenetics and genetics.

NEIL DEGRASSE TYSON: As the chemical tags that control our genes change, cells can become abnormal, triggering diseases like cancer. Take a disorder like MDS, cancer of the blood and bone marrow. It's not a diagnosis you'd ever want to hear.

SANDRA SHELBY: When I went in, he started patting my hand, and he was going, "Your blood work does not look very good at all," and that I had MDS leukemia, and that there was not a cure for it. And, basically, I had six months to live.

NEIL DEGRASSE TYSON: Was epigenetics the reason? Could the silencing of critical genes turn normal cells into cancerous ones? It's scary to think that a few misplaced tags can kill you. But it's also good news, because we've traditionally viewed cancer as a disease stemming solely from broken genes. And it's a lot harder to fix damaged genes than to rearrange epigenetic tags. In fact, we already have a few drugs that will work. Recently, Sandra Shelby and Roy Cantwell participated in one of the first clinical trials using epigenetic therapy.

JEAN PIERRE ISSA (M.D. Anderson Cancer Center): The idea of epigenetic therapy is to stay away from killing the cell. Rather, what we are trying to do is diplomacy, trying to change the instructions of the cancer cells, reminding the cell, "Hey, you're a human cell. You shouldn't be behaving this way." And we try to do that by reactivating genes.

SANDRA SHELBY: The results have been incredible, and I didn't have really any horrible side effects.

ROY CANTWELL: I am in remission. And going in the plus direction is a whole lot better than the minus direction.

NEIL DEGRASSE TYSON: In fact, half the patients in the trial are now in remission. But, while it maybe easier to fix our epigenome than our genome, messing it up is easier, too.

RANDY JIRTLE: We've got to get people thinking more about what they do. They have a responsibility for their epigenome. Their genome they inherit. But their epigenome, they potentially can alter, and particularly that of their children. And that brings in responsibility, but it also brings in hope. You're not necessarily stuck with this. You can alter this.

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We used to think that a new embryo's epigenome was completely erased and rebuilt from scratch. But this isn't completely true. Some epigenetic tags remain in place as genetic information passes from generation to generation, a process called epigenetic inheritance.

Epigenetic inheritance is an unconventional finding. It goes against the idea that inheritance happens only through the DNA code that passes from parent to offspring. It means that a parent's experiences, in the form of epigenetic tags, can be passed down to future generations.

As unconventional as it may be, there is little doubt that epigenetic inheritance is real. In fact, it explains some strange patterns of inheritance geneticists have been puzzling over for decades.

Most complex organisms develop from specialized reproductive cells (eggs and sperm in animals). Two reproductive cells meet, then they grow and divide to form every type of cell in the adult organism. In order for this process to occur, the epigenome must be erased through a process called "reprogramming."

Reprogramming is important because eggs and sperm develop from specialized cells with stable gene expression profiles. In other words, their genetic information is marked with epigenetic tags. Before the new organism can grow into a healthy embryo, the epigenetic tags must be erased.

At certain times during development (the timing varies among species), specialized cellular machinery scours the genome and erases its epigenetic tags in order to return the cells to a genetic "blank slate." Yet, for a small minority of genes, epigenetic tags make it through this process and pass unchanged from parent to offspring.

Reprogramming resets the epigenome of the early embryo so that it can form every type of cell in the body. In order to pass to the next generation, epigenetic tags must avoid being erased during reprogramming.

In mammals, about 1% of genes escape epigenetic reprogramming through a process called Imprinting.

Epigenetic marks can pass from parent to offspring in a way that completely bypasses egg or sperm, thus avoiding the epigenetic purging that happens during early development.

Most of us were taught that our traits are hard-coded in the DNA that passes from parent to offspring. Emerging information about epigenetics may lead us to a new understanding of just what inheritance is.

Nurturing behavior in rats Rat pups who receive high or low nurturing from their mothers develop epigenetic differences that affect their response to stress later in life. When the female pups become mothers themselves, the ones that received high quality care become high nurturing mothers. And the ones that received low quality care become low nurturing mothers. The nurturing behavior itself transmits epigenetic information onto the pups' DNA, without passing through egg or sperm.

Gestational diabetes Mammals can experience a hormone-triggered type of diabetes during pregnancy, known as gestational diabetes. When the mother has gestational diabetes, the developing fetus is exposed to high levels of the sugar glucose. High glucose levels trigger epigenetic changes in the daughter's DNA, increasing the likelihood that she will develop gestational diabetes herself.

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There is no doubt that epigenetic inheritance occurs in plants and fungi. There is also a good case for epigenetic inheritance in invertebrates. While many researchers remain skeptical about the possibility of epigenetic inheritance in mammals, there is some evidence that it could be happening.

(Linaria vulgaris)

Common toadflax and peloric toadflax are identical in every way, except for the shape of their flowers. They are two variants of the same plant with a difference in one gene. But its not a difference in the DNA code. Its an epigenetic difference. And peloric toadflax can pass on this epimutation to its offspring.

(Raphanus raphanistrum)

When radish plants are attacked by caterpillars, they produce distasteful chemicals and grow protective spines. The offspring of caterpillar-damaged radishes also produce these defenses, even when they live in a caterpillar-free environment. The evidence of epigenetic inheritance in this case is indirect, though its highly likely that the information passes from parent to offspring through the reproductive cells.

(Daphnia)

Female water fleas respond to chemical signals from their predators by growing protective helmets. The offspring of helmeted water fleas are also born with helmets - even in the absence of predator signals. This effect continues to the next generation, though the helmets in the grandchildren are much smaller.

Vinclozolin is a fungicide commonly used on grape plants. Feeding vinclozolin to pregnant rats causes lifelong epigenetic changes in the pups. As adults, male offspring have low sperm counts, poor fertility, and a number of disease states including prostate and kidney disease. The great-grandsons of the exposed male pups also have low sperm counts.

Two lines of evidence in this case support epigenetic inheritance. First, the low sperm count persisted into the third generation. Second, the sperm had an abnormally high level of methyl tags (a type of epigenetic tag that usually silences genes). This is the best case for epigenetic inheritance in mammals to date (Feb 2009).

Making a case for epigenetic inheritance in humans remains especially challenging.

Humans have long life spans, making it time consuming to track multiple generations. Humans have greater genetic diversity than laboratory strains of animals, making it difficult to rule out genetic differences Ethical considerations limit the amount of experimental manipulation that can take place.

But we do have a few hints that suggest that it could be happening.

Geneticists analyzed 200 years worth of harvest records from a small town in Sweden. They saw a connection between food availability (large or small harvests) in one generation and the incidence of diabetes and heart disease in later generations.

The amount of food a grandfather had to eat between the ages of 9 and 12 was especially important. This is when boys go through the slow growth period (SGP), and form the cells that will give rise to sperm. As these cells form, the epigenome is copied along with the DNA. Since the building blocks for the epigenome come from the food a boy eats, his diet could impact how faithfully the epigenome is copied. The epigenome may represent a snapshot of the boys environment that can pass through the sperm to future generations.

Proving epigenetic inheritance is not always straightforward. To provide a watertight case for epigenetic inheritance, researchers must:

Researchers face the added challenge that epigenetic changes are transient by nature. That is, the epigenome changes more rapidly than the relatively fixed DNA code. An epigenetic change that was triggered by environmental conditions may be reversed when environmental conditions change again.

Three generations at once are exposed to the same environmental conditions (diet, toxins, hormones, etc.). In order to provide a convincing case for epigenetic inheritance, an epigenetic change must be observed in the 4th generation.

Epigenetic inheritance adds another dimension to the modern picture of evolution. The genome changes slowly, through the processes of random mutation and natural selection. It takes many generations for a genetic trait to become common in a population. The epigenome, on the other hand, can change rapidly in response to signals from the environment. And epigenetic changes can happen in many individuals at once. Through epigenetic inheritance, some of the experiences of the parents may pass to future generations. At the same time, the epigenome remains flexible as environmental conditions continue to change. Epigenetic inheritance may allow an organism to continually adjust its gene expression to fit its environment - without changing its DNA code.

Fish, E.W., Shahrokh, D., Bagot, R., Caldji, C., Bredy, T., Szyf, M., and Meaney, M.J. (2004).Epigenetic programming of stress responses through variations in maternal care. Annals of the New York Academy of Science 1036: 167-180 (subscription required).

Youngson, N.A. and Whitelaw, E. (2008).Transgenerational epigenetic effects. Annual Reviews in Genomics and Human Genetics 9: 233-57 (subscription required).

Kaati, G., Bygren, L.O., Pembrey, M., and Sjostrom, J. (2007).Transgenerational response to nutrition, early life circumstances and longevity. European Journal of Human Genetics 15: 784-790.

Chong, S., and Whitelaw, E. (2004).Epigenetic germline inheritance. Current Opinion in Genetics & Development. 14: 692-696 (subscription required).

APA format:

Genetic Science Learning Center. (2013, July 15) Epigenetics & Inheritance. Retrieved September 23, 2016, from http://learn.genetics.utah.edu/content/epigenetics/inheritance/

CSE format:

Epigenetics & Inheritance [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2013 [cited 2016 Sep 23] Available from http://learn.genetics.utah.edu/content/epigenetics/inheritance/

Chicago format:

Genetic Science Learning Center. "Epigenetics & Inheritance." Learn.Genetics.July 15, 2013. Accessed September 23, 2016. http://learn.genetics.utah.edu/content/epigenetics/inheritance/.

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Epigenetics & Inheritance

What is Epigenetics?

As an organism grows and develops, carefully orchestrated chemical reactions activate and deactivate parts of the genome at strategic times and in specific locations. Epigenetics is the study of these chemical reactions and the factors that influence them.

The Epigenome at a Glance

Meet the epigenome and learn how it influences DNA.

Gene Control

Change the level of gene expression in a cell with the turn of a dial!

The Epigenome Learns From Its Experiences

Epigenetic tags record the gene-regulating signals the cell receives.

Epigenetics & Inheritance

Parents have a role in shaping the epigenomes of their offspring.

Genomic Imprinting

Certain genes are silenced during egg and sperm formation.

The epigenome dynamically responds to the environment. Stress, diet, behavior, toxins, and other factors regulate gene expression.

Insights From Identical Twins

Why do identical twins become more different as they age? See how the environment affects the epigenome in a pair of twins over time.

Lick Your Rats

What kind of mother are you? Care for a rat pup and shape its epigenome.

Nutrition & The Epigenome

What you eat can change your gene expression.

Epigenetics & The Human Brain

Epigenetic mechanisms play an important role both in normal brain function and in mental illness.

APA format:

Genetic Science Learning Center. (2013, July 15) Epigenetics. Retrieved August 05, 2016, from http://learn.genetics.utah.edu/content/epigenetics/

CSE format:

Epigenetics [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2013 [cited 2016 Aug 5] Available from http://learn.genetics.utah.edu/content/epigenetics/

Chicago format:

Genetic Science Learning Center. "Epigenetics." Learn.Genetics. July 15, 2013. Accessed August 5, 2016. http://learn.genetics.utah.edu/content/epigenetics/.

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Learn Genetics - Epigenetics

Epigenetics refers to covalent modification of DNA, protein, or RNA, resulting in changes to the function and/or regulation of these molecules, without altering their primary sequences. In some cases, epigenetic modifications are stable and passed on to future generations, but in other instances they are dynamic and change in response to environmental stimuli. Nearly every aspect of biology is influenced by epigenetics, making it one of the most important fields in science.

Why do some foods cause health problems and others make us healthy? How does stress impact our long-term well-being? Why is it that the older we get, the more likely it is that age-related illness will strike us? Unlocking the secrets behind these and other questions has the potential to revolutionize life as we know it. The emerging field of epigenetics is aiming to do just that.

The importance of nature versus nurture has long been disputed. It cannot be denied that environment greatly influences how a child grows and develops, nor can it be denied that our DNA is the blueprint that makes us who we are. Epigenetics merges these two seemingly contradictory lines of thought to explain how environmental factors cause physical modifications to DNA and its associated structures, which result in altered functions.

The most commonly known epigenetic modification is DNA methylation. Although many technologies have been developed in the past to characterize genomic DNA methylation, none of them has been able to efficiently determine DNA methylation patterns on a genomic scale. Until now.

Many cellular processes, including gene expression and DNA replication, are often regulated by mechanisms that fall into the category of classical genetics. This generally means that they are controlled by elements such as promoters, enhancers, or binding sites for repressor proteins, that are present or absent in the DNA sequence. An example of this type of regulation is the control of expression of a cellular oncogene. In normal (non-cancer) cells, this gene would not be expressed. However, in a cancer cell, this gene could have aquired a mutation, which is a change to the DNA sequence, that allows the oncogene to be expressed, and thus can contribute to the progression of cancer.

In addition to the regulatory mechanisms of classical genetics, nearly all cellular processes can also be regulated by epigenetic mechanisms. Epigenetic mechanisms can be just as important to biological events as genetic mechanisms, and can also result in stable and heritable changes. However, the big difference between genetic and epigenetic regulation is that epigenetic mechanisms do not involve a change to the DNA sequence, whereas genetic mechanisms involve the primary DNA sequence and changes or mutations to this sequence. Epigenetic regulation involves the modification of DNA and the proteins associated with DNA, which results in changes to the conformation of DNA and accessibility of other factors to DNA, without a change to the sequence of the DNA.

The Greek prefix epi means on top of or over, so the term Epigenetics literally describes regulation at a level above, or in addition to, those of genetic mechanisms. Common types of epigenetic regulation are DNA methylation and hydroxymethylation, histone modification, chromatin remodeling, and regulation by small and large non-coding RNAs. The field of epigenetics was given its name and a vague definition only ~50 years ago, but is now a dynamic and rapidly expanding discipline, challenging and revising traditional paradigms of inheritance.

Through epigenetics, the classic works of Charles Darwin, Gregor Mendel, and Jean-Baptiste Lamarck and others are now seen in different ways. As more factors influencing heredity are discovered, todays scientists are using epigenetics to decipher the roles of DNA, RNA, proteins, and environment in inheritance. The future of epigenetics will reveal the complexities of cellular differentiation, embryology, the regulation of gene expression, aging, cancer, and other diseases.

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What is Epigenetics? - Zymo Research

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Epigenetics

Insights From Identical Twins

Because identical twins develop from a single fertilized egg, they have the same genome. So any differences between twins are due to their environments, not genetics. Recent studies have shown that many environmentally induced differences are reflected in the epigenome.

Chromosome 3 pairs in each set of twins are digitally superimposed. One twin's epigenetic tags are dyed red and the other twin's tags are dyed green. When red and green overlap, that region shows up as yellow. The 50-year old twins have more epigenetic tags in different places than do 3-year-old twins.

The insight we gain from studying twins helps us to better understand how nature and nurture work together. For well over a century, researchers have compared characteristics in twins in an effort to determine the extent to which certain traits are inherited, like eye color, and which traits are learned from the environment, such as language. Typically taking place in the field of Behavioral Genetics, classical twin studies have identified a number of behavioral traits and diseases that are likely to have a genetic component, and others that are more strongly influenced by the environment.

Depending on the study and the particular trait of interest, data is collected and compared from identical or fraternal twins who have been raised together or apart. Finding similarities and differences between these sets of twins is the start to determining the degree to which nature and environment play a role in the trait of interest.

Twin studies have identified some traits that have a strong genetic component, including reading disabilities like dyslexia. Other traits, like arthritis, are more likely influenced by the environment.

Twins share the same genes but their environments become more different as they age. This unique aspect of twins makes them an excellent model for understanding how genes and the environment contribute to certain traits, especially complex behaviors and diseases.

For example, when just one twin gets a disease, researchers can look for elements in the twins' environments that are different. Or when both twins get a disease, researchers can look for genetic elements shared among similar twin pairs. These types of data are especially powerful when collected from large numbers of twins. Such studies can help pinpoint the molecular mechanism of a disease and determine the extent of environmental influence, potentially leading to the prevention and treatment of complex diseases.

To illustrate, for twins with schizophrenia, 50% identical twins share the disease, while only about 10-15% of fraternal twins do. This difference is evidence for a strong genetic component in susceptibility to schizophrenia. However, the fact that both identical twins in a pair don't develop the disease 100% of the time indicates that other factors are involved.

Identical twins (left) share all their genes and their home environment. Fraternal twins (right) also share their home environment, but only half of their genes. So a greater similarity between identical twins for a particular trait compared to fraternal twins provides evidence that genetic factors play a role.

Comparing Identical and Fraternal Twins: A higher percentage of disease incidence in both identical twins is the first indication of a genetic component. Percentages lower than 100% in identical twins indicates that DNA alone does not determine susceptibility to disease.

Wong A.H., Gottesman I., Petronis A. (2005) Phenotypic differences in genetically identical organisms: the epigenetic perspective. Human Molecular Genetics, 14: Review Issue 1, R11-R18.

Fraga, M.F. et al. (2005) Epigenetic differences arise during the lifetime of monozygotic twins. PNAS, 102:10604-9.

Poulsen P., Esteller M., Vaag A., Fraga M.F. (2007) The Epigenetic Basis of Twin Discordance in Age-Related Diseases. Pediatric Research, 61: 38R-42R (subscription required).

APA format: Genetic Science Learning Center (2014, June 22) Insights From Identical Twins. Learn.Genetics. Retrieved October 29, 2015, from http://learn.genetics.utah.edu/content/epigenetics/twins/ MLA format: Genetic Science Learning Center. "Insights From Identical Twins." Learn.Genetics 29 October 2015 <http://learn.genetics.utah.edu/content/epigenetics/twins/> Chicago format: Genetic Science Learning Center, "Insights From Identical Twins," Learn.Genetics, 22 June 2014, <http://learn.genetics.utah.edu/content/epigenetics/twins/> (29 October 2015)

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Insights From Identical Twins

There is definitely a market for a good popular science book about epigenetics, and I eagerly awaited this one. But it fell short of my expectations. It simply is too short, and too lacking in depth. For the epigenetics of inheritance and evolution, there already is an excellent book out there: Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life (Life and Mind: Philosophical Issues in Biology and Psychology) . However, the book by Jablonka & Lamb is getting a little old (in this field, things sure develop rapidly), and it lacks the issues that I was most interested in - the effects of epigenetic change on health. However, I'll restate, for the evolutionary side, the Jablonka & Lamb book is great.

Back to the book by Francis, 160 pages is just too short. I will acknowledge the great many notes and large bibliography included, but the first 160 pages are so superficial, I doubt the author finds the right audience for the notes/bibliography.

The author's writing style and explanations are fine, so if you want a quick overview on a topic of which you have zero knowledge before, this book will serve you well. However, for many of us, we must wait for a book with more depth, or a vastly expanded second edition.

For an example of excellent and in depth popular science writing, try Power, Sex, Suicide: Mitochondria and the Meaning of Life.

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Epigenetics: How Environment Shapes Our Genes

You keep using that word. I do not think it means what you think it means. The insightful Inigo Montoya.

Epigenetics is a word that seems to have caught the public imagination. This is especially true among those, both in science and without, who decry what they see as genetic determinism or at least an overly genocentric point of view. Our genes are not our fate, because epigenetics! Such-and-such disorder is not really genetic, because epigenetics! Acquired characteristics can be inherited, because epigenetics!

This molecular biology definition has really only a loose relationship to Waddingtons usage. It is obviously true that molecular mechanisms of gene regulation effect (as in mediate) the development of an organism. That is what cellular differentiation and coordinated organismal development entail. Genes are turned on, genes are turned off. Epigenetic mechanisms make the profiles of gene expression that define a particular cell type more stable, with different sets of genes held in active or inactive chromatin conformations. These two usages thus relate to very different levels one refers to the profile of gene expression of individual cell types and the other to the emergence of the phenotype of the organism.

Now, clearly, the phenotype of an organism depends largely (though by no means completely) on the profile of gene expression of its constituent cells. And there are indeed a number of examples where the behavioural phenotype of an organism has been linked to the epigenetic state of particular genes in cells in particular brain regions. Importantly, such mechanisms may provide one means whereby environmental factors or particular experiences can have long-lasting effects on an organism, by changing patterns of gene expression in particular cells in a stable manner.

Based on these kinds of examples, epigenetics has become quite a buzz-word in the fields of psychiatric and behavioural genetics, as if it provides a general molecular mechanism for all the non-genetic factors that influence an individuals phenotype.

The fact that environmental factors or extreme experiences can influence an organisms phenotype is not news. In specific cases like those described above, the effects of such factors may indeed be mediated by molecular epigenetic mechanisms. But heres the important thing even though epigenetic mechanisms may be involved in maintaining some stable traits over the lifetime of the animal, they are just that: mechanisms. Not causes. Epigenetics is not a source of variance, it is part of the mechanism whereby certain environmental factors or experiences have their effects. Furthermore, these few examples do not imply that this mechanism is involved in mediating the effects of non-genetic sources of variance more generally.

So, while epigenetic mechanisms may indeed play a role in the stable expression of certain behavioural tendencies (at least in rodents), it remains unclear how general this phenomenon is. In any case, there is no reason to think of epigenetics as a source or cause of phenotypic variance at the level of the organism. And here is a plea: if you are tempted to use the term epigenetic, make it clear which meaning you intend. If you simply mean non-genetic, there is a more precise term for this: non-genetic.

In part 2, I consider a more egregious trend emerging in the literature of late the idea that transgenerational epigenetic inheritance can provide a mechanism of heredity that explains the so-called missing heritability of psychiatric disorders. (It cant).

Continued here:
Wiring the Brain: The Trouble with Epigenetics (Part 1)

Bruce H Lipton, PhD is an internationally recognized authority in bridging science and spirit.

In 1982, Dr. Lipton began examining the principles of quantum physics and how they might be integrated into his understanding of the cell's information processing systems.

He produced breakthrough studies on the cell membrane, which revealed that this outer layer of the cell was an organic homologue of a computer chip, the cell's equivalent of a brain.

His research at Stanford University's School of Medicine, between 1987 and 1992, revealed that the environment, operating though the membrane, controlled the behavior and physiology of the cell, turning genes on and off.

Two major scientific publications derived from these studies defined the molecular pathways connecting the mind and body. Many subsequent papers by other researchers have since validated his concepts and ideas.

He is regarded as one of the leading voices of the new biology. Dr Lipton's work summarizing his findings, entitled " The Biology of Belief". His new book is Spontaneous Evolution.

http://www.brucelipton.com

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Bruce Lipton - Epigenetics - YouTube