Genome complexity: transposons control fetal development (Introduction)

by David Turell , Thursday, October 21, 2021, 14:56 (918 days ago) @ David Turell

A new study on 'junk' DNA:

https://news.berkeley.edu/2021/10/18/so-called-junk-dna-plays-critical-role-in-mammalia...

"Nearly half of our DNA has been written off as junk, the discards of evolution: sidelined or broken genes, viruses that got stuck in our genome and were dismembered or silenced, none of it relevant to the human organism or human evolution.

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"The study shows that at least one family of transposons — ancient viruses that have invaded our genome by the millions — plays a critical role in viability in the mouse, and perhaps in all mammals. When the researchers knocked out a specific transposon in mice, half their mouse pups died before birth.

"This is the first example of a piece of “junk DNA” being critical to survival in mammals.

"In mice, this transposon regulates the proliferation of cells in the early fertilized embryo and the timing of implantation in the mother’s uterus. The researchers looked in seven other mammalian species, including humans, and also found virus-derived regulatory elements linked to cell proliferation and timing of embryo implantation, suggesting that ancient viral DNA has been domesticated independently to play a crucial role in early embryonic development in all mammals.

"According to senior author Lin He, UC Berkeley professor of molecular and cell biology, the findings highlight an oft-ignored driver of evolution: viruses that integrate into our genome and get repurposed as regulators of host genes, opening up evolutionary options not available before.

“The mouse and humans share 99% of their protein coding genes in their genomes — we are very similar with each other,” He said. “So, what constitutes the differences between mice and humans? One of the major differences is gene regulation — mice and humans have the same genes, but they can be regulated differently. Transposons have the capacity to generate a lot of gene regulatory diversity and could help us to understand species-specific differences in the world.”

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"In a paper appearing last week in the journal Cell, He and her team identify the key regulatory DNA involved: a piece of a transposon — a viral promoter — that has been repurposed as a promoter for a mouse gene that produces a protein involved in cell proliferation in the developing embryo and in the timing of implantation of the embryo. A promoter is a short DNA sequence that is needed upstream of a gene in order for the gene to be transcribed and expressed.

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"While transposons are generally specific to individual species — humans and mice, for example, have largely different sets — the researchers found that different species-specific transposon families were turned on briefly before implantation in all eight mammals, including the opossum, the only mammal in the group that does not employ a placenta to implant embryos in the uterus.

“'What’s amazing is that different species have largely different transposons that are expressed in preimplantation embryos, but the global expression profiles of these transposons are nearly identical among all the mammalian species,” He said."

Comment: so transposons are not DNA junk. But more than that viral elements are involved in driving evolution, a point mentioned before in entries here. Why any viruses since some are dangerous? Why any bacteria because some are dangerous? Viruses arev seen her as useful andv we know bacteria perform all sorts of vital functions.