Animal Molecular Breeding 2024, Vol.14, No.1, 72-81 http://animalscipublisher.com/index.php/amb 74 Research on epigenetic regulation in Pomeranians requires in-depth exploration of the interactions between these mechanisms to fully understand their role in the regulation of gene expression. This not only helps to reveal the molecular mechanism of Pomeranian's unique traits, but also provides a theoretical basis for the treatment of related diseases and the improvement of dog breeds. 2 Basic Processes of DNA Methylation 2.1 Definition and discovery process of DNA methylation DNA methylation is a complex and precise epigenetic regulation mechanism. Its basic concept is to regulate gene expression by adding methyl groups at specific sites on DNA molecules (Mattei et al., 2022). The discovery of this regulatory mechanism dates back to the mid-20th century, when researchers first observed chemical differences in DNA molecules. Experiments have confirmed that this difference is closely linked to changes in gene expression, providing a foundation for subsequent in-depth research on the mechanism and function of DNA methylation. Early studies focused on regions enriched in CpG dinucleotides, which are alternately arranged between thymine and cytosine. In these regions, the researchers observed that the cytosine in the DNA molecule can undergo chemical changes after being methylated. These findings have aroused strong interest among scientists and promoted in-depth research on the mechanism of DNA methylation. In the 1960s, scientists such as Humphrey and Koch successfully identified 5-methylcytosine in DNA for the first time through nucleic acid hydrolysis and mass spectrometry analysis (Ehrlich and Wang, 1981). This discovery not only revealed the presence of the methyl group in the DNA molecule, but also determined its location in the chemical structure of DNA. This marks an important breakthrough in the substantive understanding of DNA methylation. In the early 1980s, with the advancement of gene cloning and DNA sequencing technology, scientists gradually revealed the distribution pattern and influencing factors of DNA methylation. Research during this period provided more detailed information for people to understand the dynamics of DNA methylation and its role in gene regulation. The definition and discovery of DNA methylation is an iterative and progressive process. From the initial observation of chemical differences, to the identification of the presence of 5-methylcytosine, to the detailed study of the distribution and influencing factors of DNA methylation, each stage has shed light on this key genetic regulatory mechanism. Mystery. In-depth exploration of this process has laid a solid foundation for subsequent research on the function and significance of DNA methylation in Pomeranians and other species. 2.2 Mechanism of action of DNA methyltransferase DNA methyltransferase plays a key role in the regulation of DNA methylation, and its mechanism involves a series of complex and precise biochemical processes. The mechanism of action of DNA methyltransferase will be introduced in detail below, including the two main steps of substrate binding and methyl group transfer. Substrate binding is the first step in the initiation of DNA methyltransferase action. DNA methyltransferase is able to highly selectively recognize and bind to target sequences on the DNA chain through specific domains in its structure. This selectivity is based on the base pairing rules of DNA, allowing DNA methylation to occur precisely in specific regions of the genome. During the substrate binding process, DNA methyltransferase tightly binds the target DNA sequence to its structural domain through interactions such as electrostatic interactions, hydrogen bonds, and hydrophobic forces. This highly specific substrate binding ensures accurate methylation, thereby avoiding unnecessary genomic changes. After substrate binding, the DNA methyltransferase begins the second major step, which is the transfer of the methyl group. In this process, the enzyme transfers a methyl group from a donor molecule (usually S-adenosylmethionine) through its catalytic center to a specific site on the substrate DNA. This methylated group is added to the C5 position of cytosine (Cytosine) on the DNA chain to form 5-methylcytosine. This methylation
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