Читать книгу Genomic and Epigenomic Biomarkers of Toxicology and Disease - Группа авторов - Страница 17

Epigenomics is a new, emerging area of science. Humans are exposed daily to a mixture of chemicals present in their environment. Nearly every cell in the human body has the same set of genes, but different types of cells are affected differently by these chemicals. Gene expression in cells is controlled by several mechanisms. In genomic mechanisms of toxicity and disease, the genomic DNA sequence is altered through chemical exposure. Genomic DNA sequences modified in this way are not cell- and tissue-specific. However, in some cases toxicity and diseases are caused by DNA modifications that are due to chemical exposure, but in the absence of any direct alteration in genomic DNA sequence. Such DNA modifications are known as epigenomics, where DNA methylation regulates gene expression without direct alterations in the genomic DNA sequence. In DNA methylation, gene expression occurs at the cytosine dinucleotide when a methyl group is added at position 5, producing methylcytosine (de Gannes et al. 2020; Jones 2012). Unlike genomic changes, epigenetic changes are cell- and tissue-specific. Epigenetic changes may be heritable and non-heritable. DNA methylation is associated with several human diseases, including cancer.

The epigenome is defined as heritable biological information contained outside the DNA sequence (Dolinoy and Jirtle 2008). It consists of DNA methylation, histone modifications, and microRNAs. Non-coding RNAs (ncRNAs) regulate gene expression at the transcriptional or post-translational levels without changing the genomic DNA sequence (Li and Cui 2018).