Billion-year-old lipid hints at long history of complex cells – Ars Technica

All living things that we can see around us – plants, animals, and fungi – are eukaryotes made up of complex cells. Their cells have many internal structures surrounded by membranes, which keep things like energy production separate from genetic material, and so on. Even single-celled organisms on this branch of the tree of life often have membrane-covered structures that move and rearrange to feed.

Some of the elasticity of this membrane comes courtesy of steroids. In multicellular eukaryotes, sterols perform various functions; Among other things, they are used as signaling molecules, like estrogen and testosterone. But all eukaryotes introduce various doping into their membranes, which increase their fluidity and change their curvature. So the evolution of steroid metabolism may be critical to enabling complex life.

Now, researchers have traced the origin of eukaryotic steroids to nearly a billion years in the past. The findings suggest that many branches of the eukaryotic family tree once made early versions of steroids. But our branch has developed the ability to produce more fine detail – which may have helped us outpace our relatives in the competition.

Confused schedule

To some extent, the new work involves testing an idea proposed by a biochemist decades ago Konrad Bloch. Bloch won the Nobel Prize for his discovery of the biochemical pathways that allow cells to produce steroids from simpler ancestors. In 1994, Bloch proposed that the chemical intermediates on the pathways he identified were, at some point in our evolutionary trajectories, the end products. The cells would make these less complex steroids, which have played crucial roles in their survival; However, over time, our branch has developed enzymes that further modify it in beneficial ways.

This had the ability to make sense through a variety of pieces of evidence that didn’t quite fit together. We have found microfossils 1.6 billion years old that appear to show complex cells with surface processes typically restricted to eukaryotes. This works well with the DNA evidence, which indicates that all current eukaryotes can be traced back to a common ancestor that existed at least 1.2 billion years ago, possibly as early as 1.8 billion years ago.

But we can also look for doping in ancient rocks, because the molecules are remarkably stable. But the steroids in today’s eukaryotes didn’t appear until about a billion years ago—much later than the eukaryotes themselves. This gap could be accurately explained if earlier eukaryotes used Bloch’s biochemical intermediates.

It was here that Bloch, though he was right, got something big wrong. It has been suggested that intermediates would be chemically unstable, and therefore would not survive in sediments long enough for us to find them. From this point of view, there was no point in searching.

long term

An international team of researchers decided it might be worth testing Bloch’s assumption about the durability of these molecules. So, the researchers assembled a group of molecules, subjected them to heating and accelerated aging conditions, and looked at what happened. While they lost two atoms from the side of the cyclic structures, most of the molecule survived. More importantly, no other anabolic steroids are known to produce the same molecules when they break down, so these ancient intermediates can act as tracers of steroid production.

With this information in hand, the researchers obtained samples of oil and tar from sediments dated at various points in Earth’s past. And even the oldest specimen, 1.6 billion years old, already had a lot of remnants of steroid intermediates. Researchers have isolated dozens of relatives of intermediate steroid compounds, but haven’t found any of the molecules you’d expect if modern steroids existed.

It also appears that eukaryotes were once ubiquitous. “These sterols have been detected in relatively deep and shallow water environments, microbial mats and pelagic habitats, shales and carbonates, as well as marine and possibly lacustrine ponds,” the researchers wrote.

Again, the first signs of modern steroids don’t appear until less than a billion years ago, indicating that eukaryotes—our ancestors and other branches of the evolutionary tree—flourished for nearly a billion years using molecules that are now just chemical intermediates. Various classes of modern doping also slowly appear in the geological record, indicating no spurt of innovation.

Extreme survival

The researchers propose an interesting idea that places the origin of modern eukaryotes in the geological record. It seems that eukaryotes arose during a geological time period called “boring billion,” which spanned roughly 1.8 to 0.8 billion years ago. During this time, as its name suggests, not much happened. For most of this time, geology has seen Earth’s continental plates aggregate into a supercontinent, helping to support a seemingly stable climate in which life appears to have They responded to the relative stagnation by forming equally stable ecosystems that persisted for much of this time.

While the ancestors of all modern eukaryotes would have evolved during the boring billion period, the lack of ecological disturbance probably meant that they had a hard time finding an unoccupied ecological niche. In light of this challenge, the researchers suggest that the evolution of modern amphibians could have given them the endurance needed to occupy more extreme environments, such as places where cold or high temperatures prevail or places such as mud flats that periodically dry out. This would mean that modern steroids were manufactured, but only at levels that make detection unlikely.

The boring billion ended with a spike in tectonic activity and global glaciations, which could have triggered the bacterial equivalent of a mass extinction. In the turbulent environment that followed, the ability to withstand environmental extremes permitted by modern activators might have given our ancestors an advantage, allowing them to drive all other branches of the eukaryotic tree into extinction.

Nature, 2023. DOI: 10.1038 / s41586-023-06170-w (about DOIs).