Genomics and Applied Biology 2024, Vol.15, No.3, 153-161 http://bioscipublisher.com/index.php/gab 155 In plants, for example, DNA methylation plays a significant role in coping with abiotic stresses such as drought, cold, and salinity, and similar mechanisms may be present in Bt (Akhter et al., 2021). The dynamic nature of DNA methylation, regulated by the activities of methyltransferases and demethylases, allows for precise control over gene expression in response to developmental and environmental cues (Kumar and Mohapatra, 2021). 3.2 Histone modifications in Bt Histone modifications involve the addition or removal of chemical groups to histone proteins, which can influence chromatin structure and gene expression. Common histone modifications include acetylation, methylation, phosphorylation, and ubiquitination. These modifications can either activate or repress gene expression depending on the specific chemical group added and the location of the modification on the histone protein (Neganova et al., 2020; Jin et al., 2021). For instance, histone acetylation generally leads to an open chromatin structure and active gene transcription, while histone methylation can either activate or repress transcription depending on the context (Neganova et al., 2020). The reversible nature of histone modifications makes them attractive targets for therapeutic interventions, particularly in cancer treatment, where aberrant histone modifications are often observed (Jin et al., 2021). 3.3 Role of non-coding RNAs in Bt Non-coding RNAs (ncRNAs) are a diverse class of RNA molecules that do not encode proteins but play crucial roles in regulating gene expression at the transcriptional and post-transcriptional levels. NcRNAs include microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and small interfering RNAs (siRNAs), among others. These molecules can modulate gene expression by interacting with DNA, RNA, or proteins, thereby influencing chromatin structure, RNA stability, and translation (Huang et al., 2020; Rong et al., 2021; Mathur et al., 2022). For example, ncRNAs can guide DNA methylation and histone modification machinery to specific genomic loci, thereby establishing and maintaining epigenetic states (Mathur et al., 2022). In cancer, ncRNAs have been shown to play significant roles in tumorigenesis and are being explored as potential diagnostic markers and therapeutic targets (Rong et al., 2021). The epigenetic landscape of Bt is shaped by DNA methylation, histone modifications, and the regulatory actions of non-coding RNAs. These modifications collectively contribute to the dynamic regulation of gene expression, enabling Bt to adapt to various environmental challenges and physiological demands. Understanding these mechanisms in greater detail could provide new insights into the biology of Bt and its applications in biotechnology and agriculture. 4 Mechanisms of Epigenetic Regulation in Bt 4.1 Interaction between DNA methylation and gene expression DNA methylation is a critical epigenetic mechanism that involves the addition of a methyl group to the fifth carbon of cytosine residues in DNA. This modification can switch gene expression on or off during developmental processes and in response to environmental stresses (Kumar and Mohapatra, 2021). DNA methylation typically occurs at CpG islands in gene promoter regions, leading to transcriptional repression by recruiting methyl-CpG-binding domain proteins and histone modifiers, which propagate inactive epigenetic marks like H3K9me3 (Manna et al., 2023). The dynamic nature of DNA methylation, regulated by writer and eraser proteins, allows for precise control of gene expression, contributing to genome stability and cellular differentiation (Figure 1) (Jin et al., 2021; Gray et al., 2022). 4.2 Role of histone modifications in gene regulation Histone modifications, such as methylation and acetylation, play a pivotal role in the regulation of gene expression by altering chromatin structure and accessibility. These modifications can either activate or repress transcription depending on the specific chemical groups added to histone tails. For instance, histone acetylation generally promotes gene expression by loosening chromatin structure, whereas histone methylation can have varying effects depending on the specific lysine residue modified (Jin et al., 2021). The interplay between histone modifications and other epigenetic mechanisms, such as DNA methylation and non-coding RNAs, forms a complex regulatory network that fine-tunes gene expression (Kan et al., 2021; Bure et al., 2022).
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