Saturday, April 18, 2009

Epigenetics: DNA Isn’t Everything

Two interesting reports on epigenetics from Science Daily.


Epigenetics examines the inheritance of characteristics that are not set out in the DNA sequence. Research into epigenetics has shown that environmental factors affect characteristics of organisms. These changes are sometimes passed on to the offspring.

Today, it has been scientifically proven, which molecular structures are involved: important factors are the histones, a kind of packaging material for the DNA, in order to store DNA in an ordered and space-saving way. It is now clear that these proteins have additional roles to play. Depending on the chemical group they carry, if they are acetylated or methylated, they permanently activate or deactivate genes. New methods now allow researchers to sometimes directly show which genes have been activated or deactivated by the histones.

A certain laboratory strain of the fruit fly Drosophila melanogaster has white eyes. If the surrounding temperature of the embryos, which are normally nurtured at 25 degrees Celsius, is briefly raised to 37 degrees Celsius, the flies later hatch with red eyes. If these flies are again crossed, the following generations are partly red-eyed – without further temperature treatment – even though only white-eyed flies are expected according to the rules of genetics.

Diet and epigenetics appear to be closely linked. The most well known example is that of the Agouti mice: they are yellow, fat and are prone to diabetes and cancer. If Agouti females are fed with a cocktail of vitamin B12, folic acid and cholin, directly prior to and during pregnancy, they give birth to mainly brown, slim and healthy offspring. They in turn mainly have offspring similar to themselves.
The scientists made this discovery through experiments involving two groups of rats. The first group was normal. The second group had the delivery of nutrients from their mothers' placentas restricted in a way that is equivalent to preeclampsia. The rats were examined right after birth and again at 21 days (21 days is essentially a preadolescent rat) to measure the amount of a protein, called IGF-1, that promotes normal development and growth in rats and humans. They found that the lack of nutrients caused the gene responsible for IGF-1 to significantly reduce the amount of IGF-1 produced in the body before and after birth.

As a result of this genetic adaptation, the rats were likely to grow to smaller sizes than their normal counterparts. At the same time, they were also at higher risk for a host of health problems throughout their lives, such as diabetes, growth retardation, cardiovascular disease, obesity, and neurodevelopmental delays, among others.

"Our study emphasizes that maternal–fetal health influences multiple healthcare issues across generations," said Robert Lane, professor of pediatric neonatology at the University of Utah, and one of the senior researchers involved in the study. "To reduce adult diseases such as diabetes, obesity, and cardiovascular disease, we need to understand how the maternal–fetal environment influences the health of offspring."
Genetics just got a whole lot more complicated. I wonder if epigenetics are part of the reason that genetic tests are showing limited value in predicting diseases.

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