Methylation is a chemical process in which a methyl group is transferred from one molecule to another. In DNA methylation, a methyl group couples to a specific part of DNA, thus altering a building block of the genetic material.
What is DNA methylation?
In DNA methylation, a methyl group couples to a specific part of the DNA, thus altering a building block of the genetic material. In DNA methylation, a methyl group attaches itself to specific nucleotides of DNA. DNA, also known as deoxyribonucleic acid, is the carrier of genetic information. With the help of the information stored in the DNA, proteins can be produced. The structure of DNA corresponds to that of a rope ladder, whereby the strands of the rope ladder are twisted in a helical pattern to form a so-called double helix structure. The side parts of the rope ladder are formed from sugar and phosphate residues. The rungs of the rope ladder represent organic bases. The bases of DNA are called adenine, cytosine, guanine and thymine. Two bases each connect as a pair to form a rope ladder rung. The base pairs are each formed by two complementary bases: Adenine and Thymine, and Cytosine and Guanine. A nucleotide is a molecule formed from a phosphate, a sugar, and a base component. During DNA methylation, special enzymes, the methyltransferases, attach a methyl group to the base cytosine. This is how methylcytosine is formed.
Function and task
DNA methylations are considered markers that allow the cell to use or not use certain areas of DNA. They represent a mechanism for gene regulation. Therefore, they could also be called on/off switches, since methylation of a base in most cases prevents a copy of the affected gene from transcribing DNA. DNA methylation ensures that DNA can be used in different ways without changing the DNA sequence itself. Methylation creates new information on the genome, i.e. the genetic material. This is referred to as an epigenome and the process of epigenetics. The epigenome is the explanation for the fact that identical genetic information can generate different cells. For example, human stem cells can give rise to a wide variety of tissues. A single egg cell can even give rise to an entire human being. The epigenome of the cell decides which form and function it takes on. The marked genes thus show the cell what to do for it. A muscle cell uses only the marked sections of DNA that are relevant for its work. So do nerve cells, heart cells or cells of the lung. The markings by the methyl groups are flexible. They can be removed or moved. This would make the previously deactivated DNA section active again. This flexibility is necessary because there is a constant interplay between the genome and the environment. DNA methylation picks up on these environmental influences. DNA methylations can also be stable and are inherited from one generation of cells to the next. Thus, in the healthy body, only spleen cells can ever be produced in the spleen. This ensures that the respective organ can fulfill its tasks. However, epigenetic changes can be transmitted not only from one cell to the next, but also from one generation to the next. Worms, for example, inherit immunity to certain viruses via DNA methylation.
Diseases and ailments
Pathological alterations in the epigenome have been detected in many diseases to date and have been identified as the cause of diseases in the fields of immunology, neurology, and especially oncology. In tissues affected by cancer, defects in the epigenome are almost always apparent in addition to defects in the DNA sequence per se. In tumors, an abnormal DNA methylation pattern is often observed. Methylation can be either increased or decreased. Both have far-reaching consequences for the cell. In the case of increased methylation, i.e. hypermethylation, so-called tumor suppressor genes can be inactivated. Tumor suppressor genes control the cell cycle and can induce programmed cell death of the damaged cell if cell degeneration is imminent. If the tumor suppressor genes are inactive, tumor cells can proliferate unhindered.In the case of reduced local methylation (hypomethylation), harmful DNA elements can be inadvertently activated. In the case of incorrect labeling by the methyl groups, this is also referred to as epimutation. This leads to an instability of the genome. Some carcinogenic substances have been shown to interfere with the methylation process in cells. The changes in methylation patterns differ from cancer patient to cancer patient. For example, a patient with liver cancer has different methylation patterns than a patient with prostate cancer. Researchers are increasingly able to classify tumors based on methylation patterns. Researchers can also tell how far a tumor has progressed and, at best, how it can be treated. However, the analysis of DNA methylation as a diagnostic and therapeutic method is not yet fully developed, so it will be several years before the methods are actually used outside the field of research. A very specific disease that has its origin in methylation is the ICF syndrome. It is caused by a mutation in DNA methyltransferase, the enzyme that couples the methyl groups to the nucleotides. This leads to an under-methylation of the DNA in affected individuals. The result is recurrent infections due to immunodeficiency. In addition, short stature and failure to thrive may occur.
