Inheritance of acquired traits
How to make a sperm "get smarter"
Maria Perepechaeva, "First-hand Science"
The question of the possibility of inheritance of so-called acquired traits has long been the subject of heated debate, and the revolution in molecular biology associated with the discovery of the structure of DNA and the establishment of its role in the transmission of hereditary information has only added fuel to the fire. Today we firmly know that even signs that have arisen during the life of an organism as a result of the interaction of its genotype and the external environment can be inherited. Since the DNA structure itself does not change directly, such inheritance was called epigenetic, i.e. "supra-genomic". As recent studies have shown, even the ability to learn can be transmitted to descendants in this way.
The hypothesis of inheritance of acquired traits was formulated at the beginning of the XIX century by the famous French naturalist J. B. Lamarck, and his most ardent opponent was the German zoologist A. Weisman, who developed the evolutionary doctrine on the basis of Darwin's theory of natural selection. On Russian soil, the hypothesis of inheritance of acquired traits prevailed in official science in the middle of the XX century, and the dispute between "Lamarckists" and "Weismanists" turned into an ugly "Lysenkoism", which actually led to the prohibition of genetics as a pseudoscience on the territory of the USSR until 1964, when N.S. Khrushchev was removed from the post of Secretary General.
Later, as it often happens, it turned out that both sides were right – in their own way. Indeed, during the formation of acquired traits, the "instructions" themselves for the construction of protein chains, written in DNA in the "letters" of the genetic code, do not change. But there are still "rules" according to which certain genes will work, and now they can be inherited epigenetically. In other words, there are two complementary systems of heredity: "genetic", based on the sequence of "letters"-nucleotides, and "epigenetic", based on stable activation and inactivation of genes using various mechanisms, such as methylation (attachment of a methyl group) of DNA.
An example of epigenetic regulation is the weakening of DNA methylation and DNA-binding histone proteins in metastatic cancer cells, which leads to increased expression of oncogenesis genes in them. It is also known that a number of environmental factors (nutritional characteristics, degree of stress, etc.) can epigenetically alter the DNA of germ cells and affect future generations, increasing, for example, the risk of developing diabetes or anxiety-depressive disorders. And scientists from the German Center for Neurodegenerative Diseases and the University Medical Center in Göttingen (Germany) have been researching the effects of physical and mental activity on the ability to learn both in parents and their descendants. (A popular retelling of the work can be read in the press release Does physical activity influence the health of future offspring? – VM.)
It is known that such loads have a beneficial effect on the neurons of the hippocampus – the area of the brain responsible for learning and memory, which, by the way, reduces the risk of diseases such as Alzheimer's disease. At the same time, the number and size of synapses (intercellular contacts), the number of receptors on the postsynaptic membrane and other characteristics of synaptic plasticity change in nerve cells, which changes the nature of interaction between nerve cells and forms the physical basis of learning processes.
The researchers used laboratory mice as model objects. The males were placed in cages equipped with running wheels, "houses", tunnels and other similar objects, which were moved or replaced daily, prompting the animals to explore the changed environment again and again. After making sure that such training increases the synaptic plasticity of hippocampal neurons in males, the researchers paired them with females, and then tested the resulting offspring. It turned out that representatives of the new generation inherited high brain indicators of their fathers, and they passed behavioral tests for learning ability better than mice from the control group.
Having started searching for mechanisms of inheritance of behavioral changes, scientists first established the role of RNA contained in the sperm of "smart" mice. This RNA was injected into eggs already fertilized by the spermatozoa of ordinary mice, and as a result, mice were born with increased synaptic plasticity and learning ability from birth.
In the future, scientists were able to identify specific molecules responsible for such epigenetic inheritance. First of all, these are regulatory microRNA molecules – miRNA212 and miRNA132, which are known to stimulate the formation of synapses. It turned out that these microRNAs accumulate not only in the brain, but also in the sperm cells of mice after exercise.
The next step that the researchers intend to take is to find out whether these regulatory molecules accumulate in human spermatozoa under appropriate conditions. In any case, future fathers can already be advised to mentally and physically strain themselves before having offspring. We can't do anything about genes yet, and epigenetics is in our hands!
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