Genome complexity: new review of epigenetics studies (Introduction)

by David Turell , Saturday, August 13, 2016, 21:14 (3023 days ago) @ David Turell

Surprise! Epigenetic mechanisms are different in prokaryotes and eukaryotes according to this review article: - http://www.la-press.com/the-evolution-of-epigenetics-from-prokaryotes-to-humans-and-its... - Abstract: - "The evolution process includes genetic alterations that started with prokaryotes and now continues in humans. A distinct difference between prokaryotic chromosomes and eukaryotic chromosomes involves histones. As evolution progressed, genetic alterations accumulated and a mechanism for gene selection developed. It was as if nature was experimenting to optimally utilize the gene pool without changing individual gene sequences. This mechanism is called epigenetics, as it is above the genome. Curiously, the mechanism of epigenetic regulation in prokaryotes is strikingly different from that in eukaryotes, mainly higher eukaryotes, like mammals. In fact, epigenetics plays a significant role in the conserved process of embryogenesis and human development. Malfunction of epigenetic regulation results in many types of undesirable effects, including cardiovascular disease, metabolic disorders, autoimmune diseases, and cancer. This review provides a comparative analysis and new insights into these aspects. - *** - "...the eukaryotic genome differs from prokaryotes because it is located within a membrane bound nucleus and the DNA contains histones. This histone complex consists of an octamer of histone proteins, two each of H2A, H2B, H3, and H4, along with a single H1 protein (Fig. 2). DNA strands wind around the histone complex to form nucleosomes that are used to condense DNA into a tightly coiled and compact chromosome. In eukaryotes (and certain species of Archaea), gene expression may be regulated by modification to these histones, in addition to DNA. - *** - "Epigenetics, including DNA methylation and histone modification, plays a significant role from the start of fertilization, during embryogenesis, and throughout development. Essentially, modifications in histones determine open or closed chromatin conformation in specific regions, depending mainly on the acetylation- deacetylation of lysine residues on histone tails. More specific modifications are methylation and demethylation of lysine or arginine residues, which determines the conformational identity of a gene and its ability to be transcribed. (my bold) - *** - "Thus, the process from fertilization to tissue development is tightly synchronized under control of epigenetic regulation. Aberration of this epigenetic balance in any developed tissue or organ may create an imbalance that may lead to disorders and diseases." - Comment: the main point of this very technical article is that the difference in handling DNA in the two types of organisms results in very different ways of applying epigenetic changes. The main point for me is going from unicellular organisms to multicellular is a giant step for evolution to have accomplished, and that step is no more explained than the origin of life itself. The origin of life, multicellularity, and the Cambrian explosion have no explanation in the Darwin theory. - The paragraph in bold points out that epigenetics play a huge role in early fetal formation, an interesting point for me.