Kids often rebel against their parents as they grow up, and as it turns out, so do zygotes. Feeling “too cool” for their paternal sperm’s methylation patterns, zygotes assert their individuality by “rebooting” the inherited 5mCs and starting from scratch. But up until now, it was their little secret how they pulled it off.
Researchers led by Yi Zhang at the University of North Carolina looked to uncover the zygotes’ demethylation trick by injecting newly fertilized embryos with siRNA against 12 candidate genes and using a fluorescent probe to create live cell, time-lapse images of paternal pronuclear methylation. They found that Elp3 – a component of the elongator complex – is critical in the embryo’s ability to effect demethylation.
Just to make sure they got it right, the UNC group and their Japanese colleagues conducted some more tests and found similar results:
- Three seperate assays (reporter localization, 5mC staining and bisulfite sequencing) showed Elp3 was critical to paternal DNA demethylation
- siRNA knockdown of other elongator complex components (Elp1 & Elp4) also impaired demethylation
- Testing of a mutated (dominant negative) Elp3 mRNA identified the radical SAM domain, and not the HAT domain, as important for demthylation.
Although they haven’t figured out the complete mechanism, or all of the elongator protein complex subunits, the authors suspect these findings could have big implications for stem cell research.
According to Dr. Zhang, “Many of the genes that are active in stem cells are not active in adult cells because they are methylated. If elongator can catalyze global demethylation, it could be the critical ingredient to these reprogramming cocktails, enabling us to generate stem cells quickly and safely.”
For more details about those rebellious zygotes, check out Nature, January 2010