Over the past few weeks, I have discussed how epigenetics causes differences in the phenotypes of individuals. Its effects are demonstrated through the observation of new behaviours and diseases, which gives the impression that epigenetics is in control. This isn't the case though. There are factors that influence epigenetics, and I wanted to know where the environment came into play in all of this.
There is evidence that different environmental events within an organism's life can increase or decrease the epigenetic modifications that occur to DNA sequences. Some of these alterations are then passed down to offspring, resulting in similar phenotypes observed through multiple generations. Impact from diet and toxins on the epigenome were studied (2010) in an attempt to determine how changes in the environment influence DNA methylation of an individual, and what that does to the organism's phenotype (Feil 2006; Franklin & Mansuy 2010). Their studies demonstrated that the altered expression of certain genes through DNA methylation can be passed down to offspring (Feil 2006; Franklin & Mansuy 2010). Although more research needs to be conducted, Franklin and Mansuy's study (2010) negates the idea that changes to the epigenome were lost from one generation to the next.
When a DNA sequence is epigenetically modified, it affects whether the associated gene is expressed or silenced. As cell replication occurs, these alterations need to be maintained in order for the resulting phenotype to remain consistent (Feil 2006). A methyltransferase known as DNMT1 regulates the DNA methylation of newly replicated sequences so that they are the same as the original (Feil 2006). Environmental factors can sometimes inhibit the DNMT1, altering the DNA methylation pattern in the gene and in turn, causing changes to the phenotype of the organism (Feil 2006). Feil (2006) found that changes in an organism's diet can have present these consequences. Humans with hyperhomocysteinaemia, a disease classified by high levels of homocysteine in the blood, were studied, and it was determined that these individuals showed lower levels of DNA methylation than normal DNA sequences (Feil 2006). The increase of this chemical in the cell inhibited DNMT1 causing a disease which could lead to heart problems (Feil 2006). Intake of more folic acid was found to alter the problem and increase the levels of DNA methylation (Feil 2006). In this scenario, implementing a change in diet through the introduction of more folic acid, caused a shift in the epigenetic pattern which resulted in a beneficial phenotypic change (Feil 2006).
Toxins, such as methoxychlor which is used as a pesticide on crops, are also believed to alter levels of DNA methylation in organisms exposed to them (Feil 2006; Franklin & Mansuy 2010). Animals experienced a decrease in fertility after exposure to these chemicals, and it was observed that they displayed changes in the levels of DNA methylation (Feil 2006). This phenotypic change was passed down the male germ line of rats as far as 4 generations (Feil 2006). Although more research is needed to fully understand what is causing these changes, alterations to the epigenetic patterns of organisms is thought to play a major role (Feil 2006; Franklin & Mansuy 2010). It is believed that toxins could cause similar alterations to humans and result in deformities or cancer (Feil 2006).
Very cool! There has been some cool work done on the epigenetic transmission of parental care, which is also very cool (how provision of care can result in offspring being better or worse parents). Has anybody looked at the link between diet, epigenetics and the microbiome? What about the effects of pathogens (diseases) altering the epigenome? Interesting stuff!
ReplyDeleteIt's amazing how such factors can produce effects that appear in the offspring of multiple generations. The has been some research on the epigenetics and the microbiome. They explained how epigenetics, the environment, and the microbiome were all inter-related. They impact each other in different ways. Next week, I will try to discuss more about epigenetics and the microbiome. I'm sure pathogens also alter the epigenome. There is still a lot of research that needs to be done on factors that influence the epigenome though. Researchers in the article from this week expressed the difficulty in determining whether diseases resulted from the change in the epigenome or if the change in the epigenome was a consequence of the disease. Determining the effects of pathogens might present similar problems.
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