Genome complexity: a new epigenetic form of methylation (Introduction)

by David Turell , Friday, December 04, 2020, 20:13 (1237 days ago) @ David Turell

Found in zebra fish:

https://www.sciencedaily.com/releases/2020/12/201203200557.htm

"Researchers at the Garvan Institute of Medical Research have uncovered a new form of DNA modification in the genome of zebrafish, a vertebrate animal that shares an evolutionary ancestor with humans ~400 million years ago.

"Dr Ozren Bogdanovic and his team discovered that unusually high levels of DNA repeats of the sequence 'TGCT' in the zebrafish genome undergo a modification called methylation, which may change the shape or activity of the surrounding DNA.

"We've revealed a new form of DNA methylation in zebrafish at TGCT repeats, and crucially, the enzyme that makes the modification," says Dr Bogdanovic,

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"'DNA methylation is vital to cellular function, as it controls which genes are turned on and off," explains first author of the paper, PhD student Sam Ross. "This is why the cells in our body can carry out vastly different functions, despite having almost identical DNA." (my bold)

"There are four 'base' letters that make up DNA -- C, G, T and A. In vertebrates, methylation occurs mostly where the letter G follows a C ('CG'), but there are some exceptions. One example is methylation at non-CG sites in human brain cells, aberrations of which have been linked to Rett Syndrome, a genetic disorder that impairs growth, movement and speech in children.

***

"'We were fascinated to see that methylation levels at TGCT repeats were higher than any non-CG methylation previously observed in the majority of adult vertebrate tissues," says Dr Bogdanovic. "Further, this methylation was present at high levels in the sperm and egg, absent in the fertilised egg, and then appeared again in the growing embryo, reaching its highest levels in adult tissues such as the brain and gonads. While we are yet to reveal how this modification changes gene expression, we believe TGCT methylation to be linked to the 'awakening' of the embryonic genome in zebrafish."

"The researchers further revealed that the enzyme Dnmt3ba was responsible for methylating the TGCT repeats in the zebrafish genome."

Comment: It is not surprising there is more than one methylation mechanism to modify DNA. Note the bold above.