Histone modifications regulate pre-existing biological information but they don't result in any kind of evolution
https://www.the-scientist.com/uncategorized/the-nucleosome-untangled-47599
Excerpt: "Histones serve as slates to a dizzying array of modifications, but researchers are confident they can decipher the epigenetic puzzle.
Roughly two meters of DNA gets packed into every cell nucleus in the human body. In addition to stuffing all that information into a sphere 3 to 10 microns across, the proteins that perform this task must also ensure that in each cell certain genes are constantly transcribed, while others lie ready, and other regions remain dormant, practically inaccessible. Within this cramped, chaotic space, an army of proteins must manage cellular information, decide cell fate with a moment's notice and maintain it, often passing that fate to daughter cells.
Roughly two meters of DNA gets packed into every cell nucleus in the human body. In addition to stuffing all that information into a sphere 3 to 10 microns across, the proteins that perform this task must also ensure that in each cell certain genes are constantly transcribed, while others lie ready, and other regions remain dormant, practically inaccessible. Within this cramped, chaotic space, an army of proteins must manage cellular information, decide cell fate with a moment's notice and maintain it, often passing that fate to daughter cells.
This regulation takes place in the context of the histone proteins. Two each of the four standard histones - H3, H4, H2A, and H2B - join together to form an octameric nucleosome, a spool around which roughly 146 nucleotides wind in a near double loop. By no means inert packing material, the nucleosome serves as a slate for a rich variety of modifications or "marks" that appear to play a role in managing the genome. Acetylation, methylation, phosphorylation, ubiquitination, sumoylation - the list of modifications grows monthly. Researchers have mapped as many as 50 different marks to specific amino acid residues on the histones' highly conserved N-terminal tails and elsewhere on the molecules, says Thomas Jenuwein from the Research Institute of Molecular Pathology in Vienna. "One of the challenges, I think, is to identify all of the modifications that exist," says Tony Kouzarides, of the Wellcome Trust/Cancer Research UK Gurdon Institute.
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| The list of known histone epigenetic modifications. |
Constant additions to the cast of histone marks, and the regulatory proteins that make them, remove them, or act upon their presence, put the number of potential combinations in the astronomical range. Say there were 30 different residues marked in a given nucleosome, 230 gives a billion possible combinations. A human cell has approximately only 40 million incorporated nucleosomes. Nevertheless, many appear to act together. Take one oft-described scenario on histone H3: Methylated lysine 4 (H3K4Me) and an acetylated lysine 14 (H3K14Ac) together produce an active gene state similar to a phosphorylated serine 10 in combination with acetylated lysines 14 and 9. Methylated lysine 9 is antagonistic to the serine 10 phosphorylation acting like a switch to shut down expression. And, adjacent serine-lysine pairs appear elsewhere in the histone tails.
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| Epigenetic markers function also as dials or knobs. In this way digital information (markers) is converted to analogue form of information. |
These "cross-talking" units and other signaling cascades (see image below) have an alluring quality to many researchers. A layer of information is definitely encoded in these signals, says C. David Allis, a Howard Hughes Medical Institute investigator at Rockefeller University. "As you develop from a totipotent or pluriopotent cell to a developmentally differentiated cell ... the DNA is remaining constant. It sort of tells us [that] something non-DNA is going on," says Allis, but just how much information is stored in these signals has been a matter of debate.
Epigenetic modifications are reversible
https://www.sciencedirect.com/topics/neuroscience/epigenetic-modification
Excerpt: "Epigenetic modifications play an important role in gene expression and regulation, and are involved in numerous cellular processes such as differentiation, development, and tumorigenesis. Epigenomics is the study of the complete set of epigenetic modifications on the genetic material of a cell. Epigenetic modifications are reversible modifications on a cell's DNA or histones that affect gene expression without altering the DNA sequence. Epigenomic maintenance is a continuous process that plays an important role in the stability of eukaryotic genomes by taking part in crucial biological mechanisms such as DNA repair. Two of the most characterized epigenetic modifications are DNA methylation and histone modification."
My comment: Evolution believers claim that epigenetic modifications are subject to evolution and selection. This is a pseudoscientific claim. Why? Here's because:
1. Epigenetic modifications are based on mechanisms where readers, writers and erasers are accurately doing their job along the needs of ecological adaptation. These processes are highly controlled by RNA-mediated information transmission. Nothing to do with randomness and selection.
2. Epigenetic modifications don't result in increase in biological information because they regulate how DNA is condensed and how actively it is read into transcription. Epigenetic modifications mean regulation of pre-existing biological information.
3. Epigenetic modifications are reversible. This means highly dynamic information layers.
4. Epigenetic modifications actually often result in subtle DNA errors and this leads to gradual but inevitable DNA degradation.
The theory of evolution is the most serious heresy of our time. Don't get lost.
The theory of evolution is the most serious heresy of our time. Don't get lost.
