In germ cells found in indelible epigenetic modifications

In the DNA of germ cells detected methyl modifications that remain in place even in the complete erasure other such modifications. Probably, these methylation-resistant foci responsible for the distribution of epigenetic code offspring.

It is known that stress, smoking, endured disease, famine impose on our DNA its mark. Imprint literally: we are talking about epigenetic modifications, when the sequence of the DNA is the same, and the activity of genes can change radically. (In fairness it should be noted that such modifications may occur not only at the DNA, but also to the histones — proteins that serve as DNA packaging.) Usually it is a methylated cytosine, and then the gene is inactive. However, the modification can occur in the opposite direction, when the DNA is released from the methyl groups and the genes are activated.

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Different types of epigenetic modifications: histone modifications, and DNA synthesis of miRNAs (Figure AJC1).

Epigenetic imprint indelible truth: such modifications accompany a person throughout life. Moreover, epigenetic changes can be transmitted to offspring. For example, children and grandchildren of survivors of starvation, live with the same physiological changes that happened from their parents and grandparents. In general, the transmission of epigenetic code examples accumulated many offspring, but there is an important challenge: how to explain the inheritance of epigenetic code? It can only pass through the reproductive cells. Researchers have repeatedly observed the modifications to DNA during cell maturation and always observed the same pattern: all modifications disappeared.

This process took place in the sperm and egg cells. Over time, managed to decipher the mechanism that wiped versions: methylcytosine turned into gidroksimetiltsitozin then modification stopped play in future generations of cells, that is, in other words, the modification quickly and very strongly "diluted" by becoming invisible. Some methyl groups disappeared only at the moment of fertilization. All this, however, does not answer the question of how these modifications are then recovered in the offspring.

In fact, it turned out that, so far, the researchers are not too closely followed the modifications of DNA in germ cells. Scientists from the University of Cambridge (UK) report on pages Science, they have found indelible sites in DNA, where the methyl modifications persisted throughout the maturation of sex cells — and these sites was 233. Why they are intact, the researchers can not yet say, but there may be two most likely explanations: either demethylating machine runs with errors, allowing for errors in the same places or have a special mechanism that restores the methyl groups in certain areas.

However, its main objective, scientists have made: they were able to prove that the epigenetic code can be directly transferred to the next generation. Now we only have to check whether there are similar stably modified areas in human DNA, and whether these sites are responsible for the DNA changes associated with stress, bad habits, food — in short, those environmental factors that are thought to be put on the DNA epigenetic imprint.

Prepared according to the University of Cambridge.

Category: Science

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