Maize Genomics and Genetics 2024, Vol.15, No.3, 147-159 http://cropscipublisher.com/index.php/mgg 153 disorders. For instance, the insertion of LINE-1 elements can disrupt gene function and lead to diseases such as hemophilia and Duchenne muscular dystrophy. The ongoing activity of LINE-1 in the human genome highlights the potential for transposons to cause both beneficial and deleterious mutations (Hancks and Kazazian, 2012). Transposons have a profound impact on the genetic architecture of organisms. They regulate gene expression, shape genome size and structure, generate genetic diversity, and can induce specific mutations that influence phenotypic traits. Understanding the multifaceted roles of transposons is crucial for unraveling the complexities of genome evolution and function. 6 Transposons and Epigenetic Regulation 6.1 Role of transposons in epigenetic modifications Transposons, also known as transposable elements (TEs), are mobile genetic elements that can move within a genome and have a significant impact on its structure and function. One of the primary ways transposons influence the genome is through epigenetic modifications. These modifications include DNA methylation and histone modifications, which can alter gene expression without changing the underlying DNA sequence. Transposons can serve as sites for these epigenetic marks, thereby influencing the regulation of nearby genes. For instance, transposons have been shown to be involved in the formation of new regulatory regions, such as promoters and enhancers, which can drive the evolution of gene regulatory networks (Friedli and Trono, 2015; Igolkina et al., 2019). The role of transposons in epigenetic regulation is not limited to the addition of epigenetic marks. They also play a crucial role in the dynamic regulation of these marks during development and in response to environmental changes. For example, during embryonic development, transposons are tightly regulated by epigenetic mechanisms to ensure proper gene expression patterns. This regulation is achieved through a combination of DNA methylation and histone modifications, which work together to silence transposons and prevent their potentially deleterious effects on the genome (Huda and Jordan, 2009; Friedli and Trono, 2015). 6.2 Interaction with DNA methylation and histone modification Transposons interact with various epigenetic mechanisms, including DNA methylation and histone modifications, to regulate their activity and impact on the genome. DNA methylation, particularly at CpG sites, is a well-known mechanism for silencing transposons. This methylation can prevent the transcription of transposon sequences, thereby reducing their ability to move and insert into new genomic locations. Studies have shown that mutations in DNA methyltransferases, such as MET1, can lead to the reactivation of transposons, highlighting the importance of DNA methylation in transposon silencing (Lippman et al., 2003; Mustafin and Khusnutdinova, 2018). Histone modifications also play a critical role in the regulation of transposons. Specific histone marks, such as H3K9me3 and H3K27me3, are associated with the formation of heterochromatin, a tightly packed form of DNA that is transcriptionally inactive. These histone marks can be found at transposon sequences, contributing to their silencing. For example, in Xenopus tropicalis embryos, different types of transposons are marked by distinct combinations of heterochromatic histone modifications, which vary depending on the developmental stage and the type of transposon (Kruijsbergen et al., 2017). This suggests that histone modifications are a key component of the epigenetic regulation of transposons. Histone modifications also play a critical role in the regulation of transposons. Specific histone marks, such as H3K9me3 and H3K27me3, are associated with the formation of heterochromatin, a tightly packed form of DNA that is transcriptionally inactive. These histone marks can be found at transposon sequences, contributing to their silencing. For example, in Xenopus tropicalis embryos, different types of transposons are marked by distinct combinations of heterochromatic histone modifications, which vary depending on the developmental stage and the type of transposon (Kruijsbergen et al., 2017). This suggests that histone modifications are a key component of the epigenetic regulation of transposons.
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