Epigenetics and spermatozoa
The mechanism of transmission of hereditary information bypassing DNA is revealed
Ksenia Vasilyeva, Vesti
The laws and mechanisms of transmission of genetic information have long been of interest to scientists.
To date, it is known for sure that key hereditary information is encoded in DNA and transmitted to children from their parents.
At the same time, geneticists have long suspected that there are additional ways of transmitting information. For example, it is already known that the stresses suffered by parents can affect the health and emotional state of the offspring. This effect is called epigenetic inheritance. Until now, however, it was not clear how such information is transmitted to posterity.
It seems that researchers from the University of California at Santa Cruz (UCSC) have found the answer to this question. They showed that the epigenetic information contained in the paternal chromosome can change the work of the genes of offspring and affect the development of children. Here, however, it is worth mentioning right away that so far we are talking only about experiments on animals.
Recall that epigenetic changes (so-called tags) do not change the sequence of genes in DNA, that is, they do not modify genetic information. A label is a chemical modification of either DNA itself or histones – proteins that pack a long DNA molecule into a compact form (chromosome). Nevertheless, epigenetic labels are able to "turn on" or "turn off" genes, affecting the process of their work – gene expression.
It is these epigenetic marks in histones that scientists have studied by conducting experiments with roundworms of the species Caenorhabditis elegans. According to the head of the study, Professor Susan Strome, the new work provides an answer to one of the key questions of epigenetics.
"This is a very specific question. Do sperm chromosomes with modified histones affect gene expression in offspring? Strom explains. – And the answer to it is positive."
The reason why scientists are interested in epigenetic inheritance on the paternal side is very simple. It is much more convenient to study it, since the sperm does not bring practically anything into the embryo except its chromosomes.
The egg also contains many components that can influence the development of the embryo, so it is much more difficult to trace epigenetic effects on the maternal line.
The lead author of the scientific article Sperm-inherited H3K27me3 impacts offspring transcription and development in C. elegans, published in the open access journal Nature Communications, graduate student Kiyomi Kaneshiro conducted a series of experiments under the guidance of Professor Strom.
The scientific experience was as follows: scientists removed a certain histone label in the chromosome of a sperm worm of the species C. elegans and then fertilized an egg with a modified sperm.
The key feature of the experiment was the use of two varieties of C. elegans worms: British and Hawaiian. These worms have been developing independently for a long time and have accumulated many small genetic differences.
The crossing of such genetically dissimilar test subjects played a crucial role. Thanks to this, scientists were able to determine which chromosomes were inherited from a British father, and which from a mother from Hawaii. In addition, they were able to see differences in the work of the genes of the offspring, which arose due to the removal of the histone label in the chromosomes of the father's germ cell.
Chromosomes of C. elegans worm embryos inherited from the mother are indicated in green. Photo K. Kaneshiro.
During the experiment, it turned out that after the removal of this histone label, the chromosomes of the sperm ceased to suppress the activity of certain genes in those cells of the embryo that were later to become sexual – eggs or spermatozoa. Kaneshiro discovered that these cells "turned on" neuronal genes and began to develop into neurons (nerve tissue cells).
This discovery shows that histone modification is one of the mechanisms by which the epigenetic information of the father can influence the expression of offspring genes and their development.
It is worth noting, however, that the experiment was based on the study of the consequences of artificial changes in histone proteins in sperm chromosomes. In the future, scientists will have to understand how natural environmental factors modify epigenetic tags in the germ cells of an adult organism, which are considered one of the most protected by them.
"The results of our experiments increase the likelihood that histone tags are carriers of epigenetic inheritance. We know that the external environment can change the expression of genes in somatic cells (all cells of the body, except sex cells – ed.). If natural external factors can affect the germ cells in the same way, then we assume that these changes should be inherited. However, this has yet to be shown," Kaneshiro notes in a UC Santa Cruz New study press release shows effects on offspring of epigenetic inheritance via sperm.
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