How did sex pop up? it involves the ability to fuse cells (Introduction)

by David Turell , Wednesday, February 16, 2022, 18:59 (1009 days ago) @ David Turell

Proper early controls found in Archaea:

https://www.quantamagazine.org/ancient-cells-had-sex-fusion-proteins-long-before-sex-ev...

"We animals merge a sperm and an egg; mushrooms sprout from the underground collision of fungal threads; pollen sends tubes racing through floral tissues to join ovules, creating fruit and seeds where they meet.

"Yet fusing cells like this runs contrary to the normal cellular life cycle. Cells divide into two through mitosis to reproduce asexually, but otherwise they mostly guard against major disruptions of their integrity, which could snuff out their lineage.

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"The molecular machinery that makes this part of sexual reproduction possible may have existed more than 2 billion years ago in the simple prokaryotic cells called archaea, perhaps as much as a billion years before eukaryotes and sex evolved. But the new findings also hint at an explanation for why this kind of cell fusion for sexual reproduction didn’t appear earlier in life’s history, when it seemingly could have.

"Throughout the family tree of eukaryotes, the same protein enables the cell membranes and nuclear membranes of gametes to fuse: HAP2. Because it is shared so universally among eukaryotes, “the common ancestor must have had the same mechanism,” said Michael Brandeis, a cell biologist at the Hebrew University of Jerusalem in Israel.

"But this last eukaryotic common ancestor may not have been the original bearer of the protein. HAP2 belongs to a superfamily of “fusexins,” which includes a class of proteins that some viruses use to fuse their viral envelopes with cell membranes.

"...their colleagues predicted what a hypothetical fusexin in archaea might look like, based on the structures and protein sequences of HAP2 in modern eukaryotes. Further work, including scans of genomic databases, led them to 96 archaeal genes that seemed likely to produce proteins with shapes strikingly similar to the predicted fusexin structure, with some tweaks here and there. The researchers called these archaeal genes fsxA.

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"So Podbilewicz and his colleagues brought the whispered potential of those genes to life. They incorporated fsxA into cultured hamster kidney cells and enabled the expression of the genes. By modifying some of the cells to have fluorescent red nuclei and others to have fluorescent green nuclei, the team could check whether the cells were using the putative archaeal fusexins to fuse.

"And that’s precisely what they saw. In the cells producing the FsxA protein, the green and red nuclei mixed five times as often as nuclei in unaltered cells did, because the cells with the fsxA gene were merging as if they were pairs of gametes.

"The presence of functional fusexins in the archaea could mean that the molecular tools for sex predated the evolution of eukaryotes, the researchers suggest. Based on their evolutionary analysis of the genes, they think these archaeal fusexins are the most primitive form of the protein yet seen and are likely to be billions of years old.

"Paulo Gonzalez Hofstatter, an evolutionary biologist at the University of São Paulo in Brazil who was not involved with this research, thinks that the findings fill a gap in our knowledge of evolutionary history. “But in some way, it is also a bit predictable,” he said, “because basically the whole machinery for meiosis has an archaea origin.”

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"How fusexins passed from archaea into eukaryotes is also far from obvious. For Hofstatter, the most likely explanation is direct (or “vertical”) inheritance from archaea into the lineage that became the host cell in the archaea-bacteria symbiosis underpinning all eukaryotic life. Essentially, eukaryotes may have been born this way, repurposing old tricks from their forebears.

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"Cell fusion — made possible with repurposed ancestral fusexins — may have been instrumental in the transition to eukaryotes by allowing more coordinated, large-scale genetic exchange: sexual reproduction. Such a radical shift may have been more appropriate for maintaining the fledgling eukaryotic genome."

Comment: the ability to fuse cells had to start in Archaea, since they are our ancestors. Doesn't help us understand how sexual activity was created. answer is simple if one accepts that God created evolution by His design. Anticipating necessary new processes is a logical way to design evolution. Another example of anticipating the future.