From science writer Philip Ball at Physics:
How does a liver cell remember that it’s a liver cell when it replicates? A cell’s identity is determined in part by small molecules that bind to chromosomes at specific locations. Now researchers have devised a model that seems to explain how these so-called epigenetic patterns are sustained across generations of cells. The model connects the epigenetic marking of genes with the three-dimensional structure of DNA as it is folded up inside chromosomes. It leads to a mechanism for patterns of markings to be repaired if they are disturbed by events such as gene replication.
Epigenetic markings are small molecules added onto parts of chromosomes that may act as genetic switches, silencing some genes and turning on others, so that cells become different types—liver, muscle, or heart cells, for example. Chromosomes are made of chromatin fibers, which are linear DNA molecules looped around cylindrical histone proteins, forming a “string of pearls.”
There is experimental evidence that in real cells the proteins that write epigenetic marks are recruited by proteins that read the same mark. This protein association can help to sustain epigenetic memory via a positive feedback loop: even if some marks get erased, the presence of others in the same region will encourage the erased marks to be written back again. More.
What we need now is a good hard dose of genetic fundamentalism. Genes rule. Period. 😉
See also: Epigenetics: What China’s government famine can teach us about inherited starvation effects
Epigenetic change: Lamarck, wake up, you’re wanted in the conference room!
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