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Science Square (Issue 90)
Nov 1, 2012

Childhood environment leaves its mark on DNA

Factors underlying variable DNA methylation in a human community cohort. L.L. Lam et al. PNAS October 16, 2012 vol. 109

The effect of environment on genes can be very profound. Our surroundings may not directly change our DNA sequence but it can surely dictate how our genes are transcribed. Epigenetics studies heritable changes in gene expression caused by non-genetic mechanisms, i.e. mechanisms other than the changes in the DNA sequence itself. DNA methylation is one of the major epigenetic modifications to regulate the gene expression. The addition of methyl groups on DNA sequence acts like a dimmer on a light bulb switch, which will turn certain genes on or off. A recent study showed that a person's early life experiences shape their DNA methylation patterns. The research team discovered that childhood poverty (not socioeconomic status as an adult) is highly correlated to distinct methylation marks left on genes. Although children in rich and poor households have identical sets of genes, the degree of adversity or stress at home determines which combinations of those genes are activated or silenced through differential DNA methylation. One can imagine that such epigenetic changes might cause some alterations in the gene expression program of blind people to certain environmental signals or make them even more sensitive. Perhaps such changes could make some people more adaptive to harsher life conditions, hence enhance their survival. These findings suggest that environmental conditions early in life shape our epigenomes permanently thereby influence our life experiences, health and probably many other things that we are not yet aware of.

An alien planet next door

An Earth-mass planet orbiting α Centauri B. X.Dumusque et al. Published online 17 October 2012, Nature

Astronomers have just discovered an earth-size alien planet right next to our solar system. A new earthlike planet, named Alpha Centauri, is just 4.4 light-years away. That's 40 trillion km away from earth! Although this rocky planet's mass is similar to Earth's, it orbits much closer (25 times closer than the Earth) to host star Alpha Centauri B. As a result, a year lasts 3236 days and the surface temperature of the planet reaches around to 1200 °C, which makes the planet incapable of supporting any life form we know. However, solar systems with a rocky world are usually predicted to have multiple planets. One possibility is that that Alpha Centauri A, the bigger sibling of Alpha Centauri B, might host some yet to be discovered unknown planets with more habitable zones. Although this recent discovery has sparked people's dreams to travel to another star system outside of our planetary system, such an exploration mission unfortunately seems impractical in the near future. Even a cell phone-sized probe that is accelerated to 10% of the speed of light would need to travel non-stop for 40 years to reach the target. So, what is the next best thing to do? Will it be taking photos or dropping probes on the planet's surface to study a potentially modified atmosphere? It seems like while astronomers work hard on the identification and characterization of this new star system, scientists should focus on developing super-fast propulsion systems, which will perhaps include new concepts like nuclear rockets and antimatter fusion drives.

Bad memories, substitute or suppress

Opposing Mechanisms Support the Voluntary Forgetting of Unwanted Memories
Benolt RG et al., Neuron, Volume 76, Issue 2, 450-460, 18 October 2012

For the nervous system, forgetting a memory is almost as complicated as creating one. A recent study probed the mechanism of how the brain allows us to voluntarily forget unwanted memories. Researchers utilized functional magnetic resonance imaging (fMRI) to examine the brain activity of participants who had learned associations between pairs of words and subsequently attempted to forget these memories by either blocking them out or recalling substitute memories. The fMRI results showed that two separate forgetting strategies looked equally effective yet they seemed to use different neuronal circuits in different parts of the brain. For memory suppression, dorsolateral prefrontal cortex inhibits neural activity in the hippocampus which is a critical region for recalling past memories. On the other hand, memory substitution specifically activates caudal prefrontal cortex and midventrolateral prefrontal cortex that are known to bring specific memories into awareness in the presence of distracting memories. These findings can help us to better understand the mechanisms of memory disorders such as posttraumatic stress disorder, and may ultimately help to develop effective treatments. At a more personal level, this study may direct us to explore how we deal with our unpleasant or unwanted memories. We might be surprised to realize that one approach might be working much better for us than another one. In other words, neuronal wiring in our brain might simply favor one approach over another.