Epigenetics in the post genomic era: Can behaviour change our genes?

Was Lamarck just a little bit right?

Essay , 2011 , 9 Pages , Grade: B2

Biology - Genetics / Gene Technology

Traditionally, genomic research was focused on the investigation of DNA sequence which gives rise to the diversity of phenotypes found in nature. It was undoubted that the information which is given by the genomic sequence is the sole factor which is important for the outcome for each individual organism. But since a few decades, a new concept called epigenetics has arisen and shows that we have to modify our knowledge about genetics. “Epi” derives from Greek meaning “on” or “over” and implies that epigenetic mechanisms act on genes via altering the gene expression and regulation without modifying the actual DNA sequence. In epigenetics, we can find the reason why twins (who have the exact same gene sequence) can alter in their phenotype especially concerning their susceptibility to diseases (Fraga et al. 2005; Wong et al.; 2005). Furthermore, it has the potential to answer the question how phenotypic characteristics can alter between generations without a change in the underlying genetic material.

Inhaltsverzeichnis

• Traditionally, genomic research was focused on the investigation of DNA sequence which gives rise to the diversity of phenotypes found in nature.
• Lamarck vs. Darwin:
• Broadly seen, the idea behind epigenetics is not new. It appeared 200 years ago, established by Jean - Baptiste Lamarck (1744-1829).
• Darwin (1809-1882) ascribed a greater importance to random, undirected changes providing material for natural selection.
• Epigenetics: Definition and mechanisms:
• Nowadays, there are numerous definitions but "precise definitions have remained both controversial and elusive" (Ho and Burggren; 2010).
• Methylation and demethylation are two of the main types belonging to the epigenetic mechanisms, in which a methyl group is transferred to or removed from a cytosine - mostly at CpG-islands which have an important regulative role for gene expression.
• Another epigenetic marker is given by the modification of histones, which includes acetylation, methylation and phosphorylation.
• Transgenerational epigenetic/maternal effects:
• Environmental influences can have long lasting effects on the epigenetic programming, especially when they act prenatal like in the case of the agouti mice, which is a inbred strain and thus, genetically identical.
• If we would think on a strictly DNA sequence dependant heritance of the coat colour, genetically identical parents should give birth to identically looking offspring.
• Furthermore, it was found out that the diet of the mothers can dramatically alter the heritable phenotypic change by changing the DNA methylation pattern and thus, altering the colour of the offspring (Waterland and Jirtle; 2003, Dolinoy et al., 2006).
• If this is also true in humans is not known exactly, but it could explain why twins can have different phenotypes (especially according to diseases) in different environments.
• In fact, evidences for epigenetic procedures in humans were found as well: Studies in women during famines show an epigenetic correlation between suffering from starvation in utero and the birthweight of their offspring.
• Another study showed that transgenerational epigenetic effects of food supply in the grandparents' prepubertal age were correlated with diabetes and heart disease (Kaati, 2002).
• Behaviour influences and is influenced by epigenetics:
• Recently, also evidences for a postnatal influence on the epigenome emerged.
• The best example is given by the glucocorticoid receptor gene (GR-gene) in the hippocampus of rats which is influenced by the maternal care-taking behaviour that can alter the stress response and immune capacity in the offspring: The progeny of rats which showed a higher-than-average care (e.g. measured as rate of licking and grooming) compared to rats showing a care which was below average (showed low rate of licking and grooming) displayed an increased hippocampal expression of GR, as well as a weakened hypothalamic-pituitary-adrenal responses to stress (Liu et al, 1997; Meaney and Szyf, 2005; Weaver et al 2004).
• Taking all into consideration, it can generally be said that social behaviour can change the epigenetic programming in other individuals and that these changes can have long lasting effects on the individual behaviour.
• Conclusion:
• The idea of a dynamic epigenome is based on the fact that differences between gene function and phenotype are not exclusively determined by the genomic sequence itself, but as well by reversible, but nonetheless, steady epigenetic marks.
• It gives the ability to the genome to respond quickly to changing environmental impacts by being dynamically regulated.
• Single environmental exposures can lead to long lasting effects in the phenotype.
• A full understanding of the interactions between environment (be it via physical of social impacts) and genes requires that both epigenetic and classical genetic mechanisms are taken into account.
• It was shown that epigenetic mechanisms and genetic mechanisms are both processes which have long lasting effects on the expression of genes, be it with or without the changing of the particular sequence.
• New evidences show that even behaviour has the potential to interfer with genes by influencing the epigenetic machinerie, especially by maternal determinants (see agouti mice).
• The possibility that acquired marks can be passed from parents to children has a lamarckain flavour.
• Main focus should be set on sequence specific and mediating factors that lead enzymes to genes which have the ability to modify histones and DNA and hence, determine the epigenetic status.
• References

Zielsetzung und Themenschwerpunkte

Der Essay befasst sich mit dem Konzept der Epigenetik, einem Bereich der Genetik, der sich mit vererbbaren Veränderungen der Genexpression befasst, die nicht durch Veränderungen der DNA-Sequenz selbst verursacht werden. Der Essay untersucht die Bedeutung der Epigenetik im postgenomischen Zeitalter und die Frage, ob Verhalten unsere Gene verändern kann.

• Die Rolle der Epigenetik in der Evolution und die Beziehung zu den Theorien von Lamarck und Darwin
• Epigenetische Mechanismen wie Methylierung, Histonmodifikation und nicht-kodierende RNAs
• Transgenerationale epigenetische Effekte, insbesondere durch mütterliche Einflüsse
• Der Einfluss von Verhalten auf die Epigenetik, insbesondere durch mütterliche Fürsorge
• Die Bedeutung der Epigenetik für das Verständnis von Krankheitsanfälligkeit und die Reaktion auf Umwelteinflüsse

Zusammenfassung der Kapitel

Der Essay beginnt mit einer Einführung in die traditionelle Genforschung und die Bedeutung der DNA-Sequenz für die Entstehung von Phänotypen. Dann wird das Konzept der Epigenetik vorgestellt und seine Bedeutung für das Verständnis von genetischen Prozessen hervorgehoben.

Im zweiten Kapitel werden die Theorien von Lamarck und Darwin zur Evolution verglichen und die Rolle der Vererbung erworbener Eigenschaften diskutiert. Der Essay stellt fest, dass die Epigenetik, obwohl sie nicht Lamarcks Gesamttheorie unterstützt, einen Mechanismus für die Vererbung erworbener Eigenschaften bietet.

Das dritte Kapitel befasst sich mit den Mechanismen der Epigenetik, einschließlich Methylierung, Histonmodifikation und nicht-kodierenden RNAs. Es wird erläutert, wie diese Mechanismen die Genexpression regulieren und zu stabilen, vererbbaren Veränderungen führen können.

Das vierte Kapitel untersucht transgenerationale epigenetische Effekte, insbesondere durch mütterliche Einflüsse. Das Beispiel der Agouti-Mäuse wird verwendet, um zu demonstrieren, wie die mütterliche Ernährung die epigenetische Programmierung des Nachwuchses beeinflussen und zu dauerhaften Veränderungen des Phänotyps führen kann.

Das fünfte Kapitel behandelt den Einfluss von Verhalten auf die Epigenetik. Der Essay konzentriert sich auf das Glukokortikoid-Rezeptor-Gen (GR-Gen) in Ratten und zeigt, wie mütterliche Fürsorge die epigenetische Programmierung des Nachwuchses beeinflussen und dessen Stressreaktion und Immunkapazität verändern kann.

Schlüsselwörter

Die Schlüsselwörter und Schwerpunktthemen des Textes umfassen Epigenetik, Genexpression, Vererbung erworbener Eigenschaften, Lamarck, Darwin, Methylierung, Histonmodifikation, nicht-kodierende RNAs, transgenerationale epigenetische Effekte, mütterliche Einflüsse, Verhalten, Stressreaktion, Immunkapazität, postgenomisches Zeitalter.

• College: University of Glasgow (Biology - Genetics)
• Course: Genetics BA - Level 3
• Grade: B2
• Author: Friederike Lange (Author)
• Publication Year: 2011
• Pages: 9
• Catalog Number: V179170
• ISBN (eBook): 9783656014874
• ISBN (Book): 9783656014737
• Language: English
• Tags: Darwin, Lamarck, behaviour, epigenetics