Why sex evolved; clues in Archaea (Introduction)

by David Turell , Monday, August 15, 2022, 16:37 (830 days ago) @ David Turell

From studies of DNA genes:

https://www.haaretz.com/israel-news/science/2022-08-15/ty-article/sex-cell-fusion-mecha...

"But when, why and in whom did the fusing mechanism first emerge: archaea, bacteria, eukaryotes or possibly even in viruses?

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"Now, a recently published paper in Nature Communications addresses this knotty conundrum. The answer is that fusion genes arose in archaea, the team tentatively concludes.

"The weird thing is that the mechanisms that enable sexual reproduction may have originated in said archaea around 3 billion years ago, which would be a billion years before sex with its fusing gametes emerged,

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"How did they reach this conclusion? Some archaea, they found, contain fusion proteins that turn out to be similar in structure to fusion proteins in eukaryotes and in some viruses. That can hardly be coincidence, but wait for it.

"The team determined the structure of one archaeal fusion protein, Fusexin1, and showed that it is similar in structure to eukaryotic and viral fusexins (while also having regions unique to archaea).

"Also, crucially, the archaeal gene for Fusexin1 has common sequences with “sexual” fusexins in eukaryotes. It was a surprise, Podbilewicz avows.

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"The authors then showed that these archaea proteins can fuse two eukaryotic cells just like fusion proteins in eukaryotes do. The team proved this by introducing the archaea proteins to cultured hamster cells. The hamster cells merged like gametes, they report.

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“'For now, we are sure that archaea have Fusexin1 but not bacteria,” Podbilewicz says. So count bacteria out as fusexin’s daddy.

As for estimating fusion proteins’ origin 3 billion years ago, not all archaea have fusexin – but ones who do live all over the planet, hinting at deep antiquity.

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"Archaea in general are extremophiles, thriving in environments such as the hypersaline Dead Sea in Israel, fumaroles (boiling-hot geysers, deep underground), ice in Antarctica, some living in multiple extremes, and all challenging everything we thought we knew about the limits of life. Their extremophilism is one reason some think they came first because of the extreme conditions on early Earth.

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"For one thing, “the structural similarity is very high, therefore we suggest that all fusexins derived from a common ancestor. Secondly, “the archaeal fusexin1s and the sexual fusexins (HAP2/GCS1) have some similar genetic sequences. This is one of the reasons we think that archaea or eukarya first are currently our preferred hypotheses,” he sums up – but the most parsimonious explanation is that archaea fusexin originated in archaea."

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Comment: It is generally considered that Archaea are the oldest form of life. That they carry the genes and protein for sexual fusion fits with my theory that most of the information for future functions existed in the first living DNA. This fits my form of God, who knows exactly what He wants, makes plans from the beginning, and sets an exact unchanging course. Compare that with dhw's humanized form of God who experiments, changes His mind, and allows free-for-all advances in evolution.