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Memories may be stored on your DNA
STEVEN PUETZER/PHOTONICA
This week– later, it had returned to normal, suggesting that methylation was involved in creating short-term memories in the hippocampus (Neuron, DOI: 10.1016/ j.neuron.2007.02.022). To see whether methylation plays a part in the formation of long-term memories, Miller and Sweatt repeated the experiment, this time looking at the uppermost layers of the brain, called the cortex. They found that a day after the shock, methyl groups were being removed from a gene called calcineurin and added to another –Forever in your DNA– gene. Because the exact pattern of methylation eventually stabilised and then stayed constant for seven days, when the experiment ended, the researchers say the methyl changes may be anchoring the memory of the shock into long-term memory, not just controlling a process involved in memory formation. “We think we’re seeing shortneeded to maintain the synapses term memories forming in the that make up memories. hippocampus and slowly turning They started by looking at short-term memories. When caged into long-term memories in the cortex,” says Miller, who mice are given a small electric presented the results last week shock, they normally freeze in at the Society for Neuroscience fear when returned to the cage. meeting in Washington DC. However, then injecting them “The cool idea here is that with a drug to inhibit methylation the brain could be borrowing a seemed to erase any memory of form of cellular memory from the shock. The researchers also developmental biology to use showed that in untreated mice, for what we think of as memory,” gene methylation changed says Marcelo Wood, who researches rapidly in the hippocampus long-term memory at the region of the brain for an hour University of California, Irvine. ● following the shock. But a day
Your memories are made of this DEVIN POWELL, WASHINGTON DC
REMEMBER your first kiss? Experiments in mice suggest that patterns of chemical “caps” on our DNA may be responsible for preserving such memories. To remember a particular event, a specific sequence of neurons must fire at just the right time. For this to happen, neurons must be connected in a certain way by chemical junctions called synapses. But how they last over decades, given that proteins in the brain, including those that form synapses, are destroyed and replaced constantly, is a mystery. Now Courtney Miller and David Sweatt of the University of Alabama in Birmingham say that long-term memories may be preserved by a process called DNA methylation – the addition of chemical caps called methyl groups onto our DNA. Many genes are already coated with methyl groups. When a cell divides, this “cellular memory” is passed on and tells the new cell what type it is – a kidney cell, for example. Miller and Sweatt argue that in neurons, methyl groups also help to control the exact pattern of protein expression 12 | NewScientist | 29 November 2008
THE FORMATION OF A MEMORY SHORT-TERM MEMORY: 1 HOUR AFTER ELECTRIC SHOCK MOUSE BRAIN
Removed
Methyl groups added to some genes, and removed from others, provide a pattern of gene expression that may preserve the memory of the shock
Hippocampus
LONG-TERM MEMORY: 7 DAYS AFTER ELECTRIC SHOCK
Removed Cortex
Added
Added
Dusty stars show comet smashes we were spared IT SEEMS we got off lightly in the cosmic lottery. Deadly comet impacts may be much rarer in our solar system than in others nearby. We can’t directly measure the rate of comet collisions in other solar systems but we can detect signs of the dust that such smashes kick up because the dust gets warmed by the star and so gives off infrared radiation. That radiation shows up as extra infrared in the spectrum of light coming from the star. Because such dust should dissipate quickly, it is thought to provide a good snapshot of the recent collision rate. Jane Greaves of the University of St Andrews, UK, analysed observations by the Spitzer Space Telescope and found that the vast majority of sun-like stars near us have more dust than our solar system does and therefore have had more collisions in their vicinity. Our solar
“The vast majority of sun-like stars near us have had more collisions in their vicinity than our solar system has” system may be one of the few that have been safe for life. Greaves presented her results at the Cosmic Cataclysms and Life symposium in Frascati, Italy, this month. About 25 per cent of the stars have a very strong dust signature. The rest of them have too little dust for it to be readily apparent when each spectrum is studied in isolation. Adding the measurements from these stars together, however, is like looking through a stack of slightly dusty windowpanes, making the total amount of dust easier to see. Greaves’s analysis revealed that 90 per cent of solar systems are dustier and so more collision-ridden than our own. Mark Wyatt of the University of Cambridge agrees that the rate of comet impacts is probably lower in our neck of the woods. But as the temperature of the dust found by Greaves indicates it tends to sit far from the parent stars, the impacts might not have affected life on habitable planets, which would sit closer to their star, he says. David Shiga ● www.newscientist.com
This week– later, it had returned to normal, suggesting that methylation was involved in creating short-term memories in the hippocampus (Neuron, DOI: 10.1016/ j.neuron.2007.02.022). To see whether methylation plays a part in the formation of long-term memories, Miller and Sweatt repeated the experiment, this time looking at the uppermost layers of the brain, called the cortex. They found that a day after the shock, methyl groups were being removed from a gene called calcineurin and added to another –Forever in your DNA– gene. Because the exact pattern of methylation eventually stabilised and then stayed constant for seven days, when the experiment ended, the researchers say the methyl changes may be anchoring the memory of the shock into long-term memory, not just controlling a process involved in memory formation. “We think we’re seeing shortneeded to maintain the synapses term memories forming in the that make up memories. hippocampus and slowly turning They started by looking at short-term memories. When caged into long-term memories in the cortex,” says Miller, who mice are given a small electric presented the results last week shock, they normally freeze in at the Society for Neuroscience fear when returned to the cage. meeting in Washington DC. However, then injecting them “The cool idea here is that with a drug to inhibit methylation the brain could be borrowing a seemed to erase any memory of form of cellular memory from the shock. The researchers also developmental biology to use showed that in untreated mice, for what we think of as memory,” gene methylation changed says Marcelo Wood, who researches rapidly in the hippocampus long-term memory at the region of the brain for an hour University of California, Irvine. ● following the shock. But a day
Your memories are made of this DEVIN POWELL, WASHINGTON DC
REMEMBER your first kiss? Experiments in mice suggest that patterns of chemical “caps” on our DNA may be responsible for preserving such memories. To remember a particular event, a specific sequence of neurons must fire at just the right time. For this to happen, neurons must be connected in a certain way by chemical junctions called synapses. But how they last over decades, given that proteins in the brain, including those that form synapses, are destroyed and replaced constantly, is a mystery. Now Courtney Miller and David Sweatt of the University of Alabama in Birmingham say that long-term memories may be preserved by a process called DNA methylation – the addition of chemical caps called methyl groups onto our DNA. Many genes are already coated with methyl groups. When a cell divides, this “cellular memory” is passed on and tells the new cell what type it is – a kidney cell, for example. Miller and Sweatt argue that in neurons, methyl groups also help to control the exact pattern of protein expression 12 | NewScientist | 29 November 2008
THE FORMATION OF A MEMORY SHORT-TERM MEMORY: 1 HOUR AFTER ELECTRIC SHOCK MOUSE BRAIN
Removed
Methyl groups added to some genes, and removed from others, provide a pattern of gene expression that may preserve the memory of the shock
Hippocampus
LONG-TERM MEMORY: 7 DAYS AFTER ELECTRIC SHOCK
Removed Cortex
Added
Added
Dusty stars show comet smashes we were spared IT SEEMS we got off lightly in the cosmic lottery. Deadly comet impacts may be much rarer in our solar system than in others nearby. We can’t directly measure the rate of comet collisions in other solar systems but we can detect signs of the dust that such smashes kick up because the dust gets warmed by the star and so gives off infrared radiation. That radiation shows up as extra infrared in the spectrum of light coming from the star. Because such dust should dissipate quickly, it is thought to provide a good snapshot of the recent collision rate. Jane Greaves of the University of St Andrews, UK, analysed observations by the Spitzer Space Telescope and found that the vast majority of sun-like stars near us have more dust than our solar system does and therefore have had more collisions in their vicinity. Our solar
“The vast majority of sun-like stars near us have had more collisions in their vicinity than our solar system has” system may be one of the few that have been safe for life. Greaves presented her results at the Cosmic Cataclysms and Life symposium in Frascati, Italy, this month. About 25 per cent of the stars have a very strong dust signature. The rest of them have too little dust for it to be readily apparent when each spectrum is studied in isolation. Adding the measurements from these stars together, however, is like looking through a stack of slightly dusty windowpanes, making the total amount of dust easier to see. Greaves’s analysis revealed that 90 per cent of solar systems are dustier and so more collision-ridden than our own. Mark Wyatt of the University of Cambridge agrees that the rate of comet impacts is probably lower in our neck of the woods. But as the temperature of the dust found by Greaves indicates it tends to sit far from the parent stars, the impacts might not have affected life on habitable planets, which would sit closer to their star, he says. David Shiga ● www.newscientist.com