Epigenetics: Beyond Genetics
Epigenetics refers to changes in gene expression that do not involve alterations to the genetic code itself, but rather chemical additions to genes or histones that wrap around them. These chemical additions - addition of methyl or acetyl groups - influence how genes are expressed. Epigenetic changes activate or deactivate specific genes in response to environmental and developmental signals. This process allows organisms to adapt dynamically to their environment.
DNA Methylation and Histone Modifications
One of the most studied epigenetic mechanisms is DNA methylation. In DNA methylation, a methyl group is added to cytosine bases at the sequence CG dinucleotide in a gene's promoter region. This methylation blocks the binding of transcription factors required for gene expression and results in gene silencing. Another important epigenetic mark is histone modifications. Histone proteins package DNA into structural units called nucleosomes. Histone tails can be modified by methylation, acetylation, phosphorylation and ubiquitination. These histone modifications influence the accessibility of DNA to the transcription machinery and thereby regulate gene expression. Both DNA methylation and histone modifications together modulate chromatin structure and control gene expression patterns in a cell-type and context-dependent manner.
Epigenetic Regulation During Development
Epigenetics Drugs and Diagnostic Technologies modifications play a key role in cellular differentiation during embryonic development. As a fertilized egg develops into a multi-cellular organism with diverse cell types, cells acquire distinctive epigenetic marks that lock their gene expression patterns and cellular identities. For example, DNA methylation patterns are dynamically erased and re-established during early embryonic development. This epigenetic reprogramming is crucial to reset cellular identities and drive cellular differentiation. Moreover, cell identity is maintained epigenetically in adult tissues by preserving cell type-specific gene activity and repressing alternative cell fates through heritable chromatin states. Thus, developmental fate decisions depend on dynamic changes in DNA methylation and chromatin structure directing progressive lineage specification.
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