Epigenetic regulation in early embryogenesis: mechanisms, developmental programming, and transgenerational implications.

Epigenetics are heritable features of gene expression without changes in the underlying DNA sequence and involve chemical modifications to DNA and histone proteins. The role of these mechanisms is central to the regulation of genes, determination of cell fate, embryonic development, and susceptibility or resistance to disease. Recent advances in low-input and single-cell sequencing technologies have revolutionized understanding of the early embryonic epigenome. These approaches reveal a highly dynamic epigenetic landscape characterized by extensive reprogramming events and stage-specific regulatory factors that preserve transcriptional fidelity while maintaining chromatin integrity. Experimental studies, including human data framed by the Developmental Origins of Health and Disease hypothesis, identify early embryonic and fetal development as a critical window of biological sensitivity. Adverse environmental conditions, such as maternal undernutrition, metabolic dysfunction, or other physiological stressors, may disrupt epigenetic reprogramming during this window. These could affect fetal growth, as well as provoke perpetual changes in the regulation of hormones, growth, as well as response of tissues. Thus, those persons who were exposed to less-than-optimal conditions during fetal growth face a higher risk of having perpetual disorders during their lifetime, including type 2 diabetic mellitus, cardiovascular disease, as well as disorders of metabolic syndromes. Although great progress has been made, there are still several important questions related to epigenetic marks that have been shown to avoid erasure during embryonal reprogramming. This review gathers available data regarding the control of early developments by epigenetics.