"Ancestral memory" found in mice
The same cowards as their grandfathers
Epigenetics transmits the memory of fear to sons and grandchildrenNadezhda Markina, <url>
It turned out that traumatic information changes the activity of genes by chemical modification of DNA and these changes are transmitted from fathers to children, and then to grandchildren.
We receive genes from our ancestors, in which the features of our appearance, health, and character are recorded. Memory is information about events in the environment, it is an acquired phenomenon. As we know from school textbooks, inheritance of acquired traits is Lamarckism, which was convincingly refuted by Darwin's theory of natural selection.
But our traits depend not only on what genes we possess, but also on how they work. And recently, the role of epigenetic mechanisms, not genetic ones, has become more and more obvious, that is, the processes lying "near the genes".
We are talking about chemical modifications of a DNA molecule that do not affect the sequence of nucleotides that it consists of. Not mutations, when one nucleotide is replaced by another, but these external chemical modifications affect the work of a particular gene. First of all, they include DNA methylation. This is the addition of a methyl group (CH3) to the nitrogenous base cytosine, which occurs as part of the CpG dinucleotide (cytosine and guanine).
Methylation of a gene, depending on the degree, weakens or completely stops its expression – protein synthesis, which includes two subsequent stages, transcription and translation. By methylation, scientists explain a variety of phenomena that cannot be explained by anything else. For example, the fact that people carry the imprint of a difficult childhood all their lives, how nutrition affects the work of genes and why the children of middle-aged fathers live longer.
All this has to do with a study published in the latest issue of the journal Nature neuroscience (Brian G Dias & Kerry J Ressler, Parental olfactory experience influences behavior and neural structure in subsequent generations).
Brian Diaz and Kerry Ressler from Emory University Medical Center in Atlanta experimentally showed the transmission of smell memory through a generation of mice – from grandfathers to grandchildren.
They conducted a rigorous experiment and, using all sorts of control options, proved that this is a biological, not a social transmission and that it occurs by transferring DNA methylation through germ cells.
The experiment was as follows. We took male mice and developed in them a fear of a certain smell – the smell of the substance acetophenone. Actually, they developed a conditioned reflex of avoidance – after the supply of this smell was accompanied by an electric shock, the mice began to be afraid of it and, when they felt the smell, rushed to run without waiting for an electric shock. Then the males, frightened by acetophenone, mated with the females, and their cubs were born. Biologists demonstrated the smell of acetophenone to grown-up children and found that they had increased sensitivity to it. Although no one electrocuted them, the presentation of the smell caused the mice to have a so-called startle reaction (English startle – to frighten, excite) – they shuddered and either froze, or jumped, or tried to run.
Even more surprisingly, the fear of smell remained in the third generation – the grandchildren of once frightened males showed increased sensitivity to the smell of acetophenone.
Naturally, control groups of mice were involved in the experiment – these were the descendants of those males who were not "scared" by any smell, as well as the descendants of males who were electrocuted with another smell – propanol. So, neither those nor other control mice showed a fright reaction to the smell of acetophenone.
Then the researchers began to understand the anatomy of smell perception. They found out that the smell of acetophenone excited a certain group of neurons in the olfactory epithelium of the nasal cavity of mice (Olfr151 receptor), as well as a certain group of neurons in the olfactory lobe of the brain.
It turned out that the increased sensitivity to this smell in the direct and grandchild descendants of the original mice was accompanied by an increase in the number of excited neurons.
So, the memory of the smell was passed on to descendants and even through a generation. But maybe this can be explained by social reasons, that is, the influence of parental education? Having asked themselves such a question, the scientists set up an experiment in which they used "conception in vitro" with the subsequent planting of embryos to surrogate mothers. The resulting cubs never saw their "scared" fathers and could not learn anything from them.
There remained an epigenetic transmission pathway, which scientists tested directly. They looked at the DNA region where the Olfr151 receptor gene is located and found that the methylation of this gene in the children and grandchildren of "frightened" males is below normal. This means that the gene is working hard and, accordingly, the olfactory receptor for the smell of acetophenone is working in an enhanced mode.
And this marker of this gene is reduced methylation, since it passes into spermatozoa, through them it is transmitted to the next generation. There are no other explanations for the "memory of grandfathers".
But it should be emphasized that this scheme works only for "paternal" and "grandfathered" memory, and not for "maternal". Why? Because DNA changes acquired during life are transmitted to sperm cells, but are not transmitted to eggs. There is a fundamental difference between the development of both – spermatogenesis occurs throughout the life of a man, and a woman is born with a full set of eggs.
The journal Nature Neuroscience published expert opinions on this study. "Epigenetic inheritance through generations is quite common in plants, but much less common in animals," notes Professor Wolf Reik, head of the Babraham Institute's epigenetics research program. "The article by Diaz and Ressler demonstrated that transmission through generations exists and it has epigenetic mechanisms."
Marcus Pembrey, professor of pediatrics and genetics at University College London, believes that the study demonstrated a possible mechanism for the transmission of traumatic experiences through generations, ancestral memory.
"A similar phenomenon was observed by Pavlov 90 years ago," he notes, "developing a food conditioned reflex. He found that in the next generations of dogs, this reflex is developed faster and faster.
But throughout the XX century, this phenomenon has not received due attention. If he lived today, Pavlov would have found an explanation for his observations in the article by Diaz and Ressler. The time has come for medicine to take seriously the possibilities of transmission through generations in humans. I believe we will not be able to understand the causes of many neurological disorders, obesity, diabetes or metabolic syndrome without taking into account the possibility of transmission through the generation."
Portal "Eternal youth" http://vechnayamolodost.ru02.12.2013