Explanation of epigenetics

[historian3x]

So I was reading over at Wikipedia about anorexia nervosa and seen something about epigenetics that had sparked my curiousity.

 

http://en.wikipedia.org/wiki/Anoretic

 

"epigenetics: Epigenetic mechanisms: are means by which genetic mutations are caused by environmental effects that alter gene expression via methods such as DNA methylation, these are independent of and do not alter the underlying DNA sequence. They are heritable, as was shown in the Överkalix study, but also may occur throughout the lifespan, and are potentially reversible. Dysregulation of dopaminergic neurotransmission and Atrial natriuretic peptide homeostasis resulting from epigenetic mechanisms has been implicated in various eating disorders.[74] "We conclude that epigenetic mechanisms may contribute to the known alterations of ANP homeostasis in women with eating disorders."[74][75]"

 

My question is that it says there are mutations caused by environmental factors that alter gene expression, but yet seem not to alter DNA sequence. Can someone please explain to someone who doesn't know much about genetics?

 

Another question is about mutations being reversible. Can someone elaborate on the possibility of mutations being reversible because I was under the impression that it was fixed once it occurs. Is it possible to revert to normal gene expression from mutations?

 

Thanks

[immortal]

So I was reading over at Wikipedia about anorexia nervosa and seen something about epigenetics that had sparked my curiousity.

 

http://en.wikipedia.org/wiki/Anoretic

 

"epigenetics: Epigenetic mechanisms: are means by which genetic mutations are caused by environmental effects that alter gene expression via methods such as DNA methylation, these are independent of and do not alter the underlying DNA sequence. They are heritable, as was shown in the Överkalix study, but also may occur throughout the lifespan, and are potentially reversible. Dysregulation of dopaminergic neurotransmission and Atrial natriuretic peptide homeostasis resulting from epigenetic mechanisms has been implicated in various eating disorders.[74] "We conclude that epigenetic mechanisms may contribute to the known alterations of ANP homeostasis in women with eating disorders."[74][75]"

 

My question is that it says there are mutations caused by environmental factors that alter gene expression, but yet seem not to alter DNA sequence. Can someone please explain to someone who doesn't know much about genetics?

 

Another question is about mutations being reversible. Can someone elaborate on the possibility of mutations being reversible because I was under the impression that it was fixed once it occurs. Is it possible to revert to normal gene expression from mutations?

 

Thanks

 

There are various types of genetic mutations, point mutations are one type of mutation where a change of base occurs at one of the three places of a Codon and hence in these type of mutations DNA sequence is altered but there are other type of mutations like regulatory mutations which doesn't change the sequence of the target gene but instead try suppress or express the gene expression and and these genetic changes are normally induced by environment factors.

 

Mutations cannot be reversible but it is indeed possible to reverse a gene expression just like you can switch on or switch off a light bulb. To know more read about RNA interference and how prions regulate phenotypes in certain microbes at different times of the seasons.

[CharonY]

The scope of the question is actually quite broad and not easily addressable in a short post. One has to understand that DNA is not a simple static molecule in which only the sequence of bases carries information, but it also has a certain dynamics which involves e.g. proteins that control actual expression of encoded genes.

Among the factors that are actually inheritable, DNA modification (i.e. methylation). By methylating specific areas on the DNA, expression can be altered. These methylation patterns can be maintained and passed on.

Reversion of mutations can occur on several levels. Either an additional mutation restores the former phenotype, or, the mutation site can mutate again back to the original base (or one that results in the same encoded AA, usually the third base in a triplet). The latter is not terribly common, but may be selected for.

 

This means that while for any individual cell a reversion is unlikely to happen, within a large cell pool those revertants (i.e. cells that restore the original codon or a homologous one) may be selected for if cell functions are inhibited by the mutation. Hence, the rate of revertants may be higher than expected (again, provided there is positive selection).

For regulatory areas more leeway may be there in terms of restoring functions, but one must keep in mind that regulation is based on equilibrium reactions and there are generally only quantitative changes (rather than on/off regulation). Note that one should not confuse it with epigenetic control as the modification of DNA (i.e. methylation) is generally not considered a form of mutation.

[ewmon]

I read "genetic mutations" instead as "mutations involving gene expression", and that it can involve the gene itself in the DNA of a chromosome, or anywhere along the path that produces the final product. To quote your Wikipedia source —

 

Epigenetic mechanisms are ... genetic mutations ... caused by environmental effects that alter gene expression [but] do not alter the underlying DNA sequence

Mutations that don't alter DNA. The classic (and probably most common) form of genetic expression is where a simple sequence of DNA result in a simple string of amino acids that compose the protein being expressed. However, a gene can produce a protein in other ways. The gene can be in two different sections on the chromosome, and a "helper" molecule binds together the two resulting protein sections. Sometimes the protein produced contains an extra amino acid or lacks an amino acid, and a "helper" molecule deletes or adds the amino acid in question. These three methods can be part of gene expression, and they are far from simple. If something makes the "helper" molecule scarce, then it can't do its job fully, and the gene expression is interrupted (without involving the DNA).

 

Reversible mutations. I am a good example. As a teenager, I suddenly became lactase deficient (aka "lactose intolerant") because I lacked the enzyme lactase that helps digest lactose (ie, the sugar in milk), and so, I could not tolerate milk in my diet, but the same thing happened to my brothers at the same time (and our ages spanned eight years). So, it was environmental (ie, something in our environment triggered it) and not developmental (ie, something at a certain age in our development triggered it). Twenty years later, I became lactase un-deficient and could tolerate milk products again, for which I was very thankful (ice cream, hot cocoa, etc ).

 

... but I defer to CharonY (who knows more than I do)

[MonDie]

Sometimes mutations involve genes being duplicated, so there are more copies of the original gene within the DNA. Warning: Speculations Ahead I imagine that the effects of such "copy number" mutations would be reversed easily. If a mutation in the new copy renders its products useless, if the new copy is "translocated" to an inactive spot, or if the new copy is totally removed, the result is probably going to be a reversion to the old phenotype, albeit with an altered DNA sequence.

[CharonY]

Sometimes mutations involve genes being duplicated, so there are more copies of the original gene within the DNA. Warning: Speculations Ahead I imagine that the effects of such "copy number" mutations would be reversed easily. If a mutation in the new copy renders its products useless, if the new copy is "translocated" to an inactive spot, or if the new copy is totally removed, the result is probably going to be a reversion to the old phenotype, albeit with an altered DNA sequence.

 

A) gene duplication is a classic type of DNA mutation and therefore not considered epigenetics.

B) depending on gene, often there is no specific phenotype associated with it. They are only expressed if the upstream region is also duplicated.

C) in terms of reversals it is important to distinguish between reversals of phenotype and genotype. With gene duplication the latter is extremely rare, for the former see B. In cases where it is, the regulation is mostly moderating effects

D) what is an inactive spot and how would it be move there?

[MonDie]

An inactive spot would be a place where the gene doesn't get translated very often. I don't know exactly what might make it not get translated. Perhaps there is a repressor protein blocking its translation.

The gene would be moved to an inactive spot through a translocation mutation.

 

Alas, I've only read the unit on genetics in my "essential biology" textbook, and therein are the boundaries of my understanding.

 

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I didn't think the OP was talking about epigenetic changes in particular when they asked whether a mutation can be reversed.

Edited December 12, 2012 by Mondays Assignment: Die