Early embryology; zygote DNA controls (Introduction)

by David Turell , Tuesday, December 06, 2016, 19:05 (2909 days ago) @ David Turell

When sperm and egg meet they formed a combined DNA in a cell called a zygote. From this union any type of necessary cell is developed. A liver cell is not a kidney cell because they have turned on different codes in their DNA. Therefore a zygote's DNA is kept under control as stem cells are formed and those controls are removed on arrival at the site of the new organ formation. this research is a hint of how it all must work:

https://www.sciencedaily.com/releases/2016/12/161206094241.htm

"'We are particularly interested in the events that are required when the cells are to divide so many times and develop in so many different ways, for example cells from the skin, and the liver, and the heart," the researcher explains. In a current study, she and her team approached this problem by examining the so-called chromatin, which refers to the DNA and the proteins (histones) around it. "We looked at how certain histones are changed after fertilization, which allowed us to explain a new mechanism."

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"The authors discovered that the molecule Suv4-20h2, a so-called histone methyltransferase, travels over the chromatin and attaches small chemical changes (dubbed methyl groups) to the histones. When the addition of these chemical changes occurs, the cell is constrained in its division and development, Torres-Padilla explains. But once fertilization occurs, the attachments disappear and the fertilised ovum can develop into a new organism.

"In order to confirm these results, the researchers used an experimental model to test the effect of keeping the Suv4-20h2 active in the fertilized ovum. "We were able to demonstrate that in this case, the methyl groups remain on the histones," explains first author Andre Eid, doctoral candidate at the IES. "This arrests the development and the cells did not progress beyond the first division."

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"'In further experiments, the team was able to show that this mechanism is probably based on the fact that the methyl groups on the histones lead to a defect during the duplication of the genetic material, referred to as replication. This defect causes then a replication 'check point', whereby the cell cycle comes to a standstill.
"Our results have given us insight into the complex connections between the chromatin and the ability of cells to develop into other types of cells -- so-called totipotency," Torres-Padilla states as she puts the results into perspective. This is an important step both for human embryology."

Comment: The control molecule over methylation is an enzyme, which means it is a giant molecule, again raising the issue of how did evolution find it for its specific functional capacities? This shows that methylation is not just epigenetic controls but embryological controls to allow stem cells from a dividing zygote to differentiate into specific cell types, hundreds of them. Not be chance!