• Speedy evolution from single-cellular to multi-cellular replicated in yeast
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[IMG]http://s.ph-cdn.com/tmpl/v3/img/logo.gif[/IMG][IMG]http://i1.nyt.com/images/misc/nytlogo379x64.gif[/IMG] [release] [IMG]http://cdn.physorg.com/newman/gfx/news/hires/2012/biologistsre.jpg[/IMG] Green cells are undergoing cell death, a cellular division-of-labor--fostering new life. Credit: Will Ratcliff and Mike Travisano [/release] [release] [b](PhysOrg.com) -- More than 500 million years ago, single-celled organisms on Earth's surface began forming multi-cellular clusters that ultimately became plants and animals.[/b] Just how that happened is a question that has eluded evolutionary biologists. Now scientists have replicated that key step in the laboratory using common Brewer's yeast, a single-celled organism. The yeast "evolved" into multi-cellular clusters that work together cooperatively, reproduce and adapt to their environment--in essence, they became precursors to life on Earth as it is today. The results are published in this week's issue of the journal Proceedings of the National Academy of Sciences (PNAS). "The finding that the division-of-labor evolves so quickly and repeatedly in these 'snowflake' clusters is a big surprise," says George Gilchrist, acting deputy division director of the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research. "The first step toward multi-cellular complexity seems to be less of an evolutionary hurdle than theory would suggest," says Gilchrist. "This will stimulate a lot of important research questions." It all started two years ago with a casual comment over coffee that bridging the famous multi-cellularity gap would be "just about the coolest thing we could do," recalled Will Ratcliff and Michael Travisano, scientists at the University of Minnesota (UMN) and authors of the PNAS paper. Other authors of the paper are Ford Denison and Mark Borrello of UMN. Then came the big surprise: it wasn't that difficult. Using yeast cells, culture media and a centrifuge, it only took the biologists one experiment conducted over about 60 days. [img_thumb]http://cdn.physorg.com/newman/gfx/news/hires/2012/1-biologistsre.jpg[/img_thumb] Multi-cellular 'snowflake' yeast images with a blue cell-wall stain and red dead-cell stain. Credit: Will Ratcliff and Mike Travisano "I don't think anyone had ever tried it before," says Ratcliff. "There aren't many scientists doing experimental evolution, and they're trying to answer questions about evolution, not recreate it." The results have earned praise from evolutionary biologists around the world. "To understand why the world is full of plants and animals, including humans, we need to know how one-celled organisms made the switch to living as a group, as multi-celled organisms," says Sam Scheiner, program director in NSF's Division of Environmental Biology. "This study is the first to experimentally observe that transition," says Scheiner, "providing a look at an event that took place hundreds of millions of years ago." In essence, here's how the experiments worked: The scientists chose Brewer's yeast, or Saccharomyces cerevisiae, a species of yeast used since ancient times to make bread and beer because it is abundant in nature and grows easily. They added it to nutrient-rich culture media and allowed the cells to grow for a day in test tubes. Then they used a centrifuge to stratify the contents by weight. As the mixture settled, cell clusters landed on the bottom of the tubes faster because they are heavier. The biologists removed the clusters, transferred them to fresh media, and agitated them again. [img_thumb]http://cdn.physorg.com/newman/gfx/news/hires/2012/2-biologistsre.jpg[/img_thumb] First steps in the transition to multi-cellularity: 'snowflake' yeast with dead cells stained red. Credit: Will Ratcliff and Mike Travisano Sixty cycles later, the clusters--now hundreds of cells--looked like spherical snowflakes. Analysis showed that the clusters were not just groups of random cells that adhered to each other, but related cells that remained attached following cell division. That was significant because it meant that they were genetically similar, which promotes cooperation. When the clusters reached a critical size, some cells died off in a process known as apoptosis to allow offspring to separate. The offspring reproduced only after they attained the size of their parents. [img_thumb]http://cdn.physorg.com/newman/gfx/news/hires/2012/multi_cellular5_h.jpg[/img_thumb] Multi-cellular yeast individuals containing central dead cells, which promote reproduction. Credit: Will Ratcliff and Mike Travisano "A cluster alone isn't multi-cellular," Ratcliff says. "But when cells in a cluster cooperate, make sacrifices for the common good, and adapt to change, that's an evolutionary transition to multi-cellularity." In order for multi-cellular organisms to form, most cells need to sacrifice their ability to reproduce, an altruistic action that favors the whole but not the individual, Ratcliff says. For example, all cells in the human body are essentially a support system that allows sperm and eggs to pass DNA along to the next generation. Thus multi-cellularity is by its nature very cooperative. "Some of the best competitors in nature are those that engage in cooperation, and our experiment bears that out," says Travisano. Evolutionary biologists have estimated that multi-cellularity evolved independently in about 25 groups. Travisano and Ratcliff wonder why it didn't evolve more often since it's not that difficult to recreate in a lab. Considering that trillions of one-celled organisms lived on Earth for millions of years, it seems like it should have, Ratcliff says. That may be a question the biologists will answer in the future using the fossil record for thousands of generations of multi-cellular clusters, which are stored in a freezer in Travisano's lab. Since the frozen samples contain multiple cell lines that independently became multi-cellular, the researchers can compare them to learn whether similar or different mechanisms and genes were responsible in each case, Travisano says. The next steps will be to look at the role of multi-cellularity in cancer, aging and other critical areas of biology. "Multi-cellular yeast is a valuable resource for investigating a wide variety of medically and biologically important topics," Travisano says. "Cancer was recently described as a fossil from the origin of multi-cellularity, which can be directly investigated with the yeast system. "Similarly the origins of aging, development and the evolution of complex morphologies are open to direct experimental investigation that would otherwise be difficult or impossible." Our ancestors were single-celled microbes for about three billion years before they evolved bodies. But in a laboratory at the University of Minnesota, brewer’s yeast cells can evolve primitive bodies in about two weeks. The transition to multicellular life has long intrigued evolutionary biologists. The cells in our bodies have evolved to cooperate with exquisite precision. The human body has more than 200 types of cells, each dedicated to a different job. And a vast majority of the 100 trillion cells in our bodies sacrifice their own long-term legacy: Only eggs and sperm have a chance to survive our own death. These demands for cooperation and sacrifice ought to make it hard for single-celled life to become multicellular. Yet animals, plants and other life forms have evolved bodies. “We know that multicellularity has evolved in different lineages at least 25 times in the history of life,” said William Ratcliff, a postdoctoral researcher at the University of Minnesota. Dr. Ratcliff and his adviser, Michael Travisano, are experts in experimental evolution. They design experiments in which microbes can evolve interesting new traits within weeks. “We were sitting in his office drinking coffee, talking about what would be the coolest thing you could do in the lab,” Dr. Ratcliff said. “O.K., the origin of life would be too hard. But other than the origin of life, what would be the coolest thing?” They decided it would be observing single-celled microbes evolving a primitive form of multicellularity. The scientists designed an experiment with brewer’s yeast, which normally lives as single cells, feeding on sugar and budding off daughter cells to reproduce. Dr. Ratcliff and his colleagues set up an experiment that might favor multicellularity in yeast. They reared lines of yeast, starting from a single cell, in 10 flasks of broth. They kept the flasks shaking for a day and then let the yeast settle. The scientists then took out a drop of the settled yeast cells and transferred it to a fresh flask, where the yeast could continue to grow. In this experiment, natural selection favored any new mutation that would let the yeast fall quickly. Yeast cells that were still floating high in the broth would not have a chance to be delivered to the next flask. In a matter of weeks, Dr. Ratcliff noticed, the yeast was sinking fast, forming a cloudy layer at the bottom of the flasks. He put the yeast under a microscope and discovered that most of it was no longer growing as single cells. Instead, the broth was dominated by snowflake-shaped clusters of hundreds of cells stuck together. These were not clumps of unrelated cells, he found. When he isolated individual cells and let them grow, they formed new snowflakes. Instead of drifting away, newly budded yeast cells remained stuck to their parents. By staying stuck together, these yeast clusters fell faster than individual cells. A single cell needs a few hours to grow to “adult” size, Dr. Ratcliff found. After it matures, its growing branches start to press against one another until they snap apart. These broken branches are yeast versions of plant cuttings: Each one grows into a snowflake of its own, which then snaps apart in turn. Dr. Ratcliff also found that this new form of reproduction is possible only because some of the yeast cells make the ultimate sacrifice. Once a snowflake reaches adult size, a fraction of the cells commit suicide. “The cells that kill themselves act as weak links,” he said. The scientists describe their experiments in a paper being published this week in Proceedings of the National Academy of Sciences. “This is a really interesting and important study,” said Richard Lenski, a biologist at Michigan State University and the editor of the paper. “It shows that a major transition in evolution — going from unicellular to multicellular life forms — might not be as hard to achieve as most biologists have long thought.” Dr. Ratcliff suspects that the transformation of the yeast in his lab may offer hints about how animals and other lineages became multicellular hundreds of millions of years ago. “Forming clusters isn’t a freaky yeast thing,” he said. The closest single-celled relatives of animals, called choanoflagellates, also sometimes grow as clusters of cells. Animals and plants did not evolve inside flasks, of course. But natural conditions could have favored clusters of cells. They might have been harder for predators to eat, for example. A cluster of cells might also be able to feed more efficiently in some cases. Dr. Ratcliff and his colleagues are now examining 25 genomes of the evolved yeast, looking for the mutations that gave them snowflake bodies. Meanwhile, their yeast continues to evolve. Once the cells gain the ability to form snowflakes, they become better adapted to multicellular life. They snap off smaller branches, allowing them to reproduce faster. Dr. Ratcliff would not go into detail about where the yeast evolution was going until he published the latest results. “We’re getting really interesting things happening now” was all he would say. [/release] [URL="http://www.pnas.org/cgi/doi/10.1073/pnas.1115323109"]More information[/URL] [URL="http://www.physorg.com/news/2012-01-scientists-replicate-key-evolutionary-life.html"]Source #1[/URL] [URL="http://www.nytimes.com/2012/01/17/science/yeast-reveals-how-fast-a-cell-can-form-a-body.html"]Source #2[/URL]
Now all they have to answer is how the first cell was formed.
-snip dumb-
It was either the perfect elements in perfect conditions, or aliens.
[QUOTE=valkery;34252006]Now all they have to answer is how the first cell was formed.[/QUOTE] [url=http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment]This[/url] [url=http://en.wikipedia.org/wiki/Threose_nucleic_acid]might[/url] [url=http://www.biomedcentral.com/1471-2148/10/187]answer[/url] [url=http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment]your[/url] [url=http://www.scientificamerican.com/article.cfm?id=a-precursor-of-rna]question[/url]
[QUOTE=Helix Alioth;34252062][url=http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment]This[/url] [url=http://en.wikipedia.org/wiki/Threose_nucleic_acid]might[/url] [url=http://www.biomedcentral.com/1471-2148/10/187]answer[/url] [url=http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment]your[/url] [url=http://www.scientificamerican.com/article.cfm?id=a-precursor-of-rna]question[/url][/QUOTE] The wikipedia article and the fifth link both explicetly state that TNA has to be synthesised. I don't think it was present at the forming of life.
[QUOTE=valkery;34252119]The wikipedia article and the fifth link both explicetly state that TNA has to be synthesised. I don't think it was present at the forming of life.[/QUOTE] I will listen to you because you seem like you know exactly what was present when life formed a few hundred million years ago.
[QUOTE=Helix Alioth;34252062][url=http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment]This[/url] [url=http://en.wikipedia.org/wiki/Threose_nucleic_acid]might[/url] [url=http://www.biomedcentral.com/1471-2148/10/187]answer[/url] [url=http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment]your[/url] [url=http://www.scientificamerican.com/article.cfm?id=a-precursor-of-rna]question[/url][/QUOTE] OH SNAP SON PROFESSOR LENSKI IN DA HOUSE
[QUOTE=valkery;34252119]The wikipedia article and the fifth link both explicetly state that TNA has to be synthesised. I don't think it was present at the forming of life.[/QUOTE] We've yet to create a black hole, and they cannot be directly detected. I don't think they exist.
[img]http://www.wicked-vision.com/images_rv/E/Evolution_cover.jpg[/img]
[QUOTE=Xenocidebot;34254595]We've yet to create a black hole, and they cannot be directly detected. I don't think they exist.[/QUOTE] That is not what I am saying. I am saying that TNA, at least up until this point has not been found in nature. Unless something synthesized TNA at the creation of the earth, I doubt that TNA was present.
[QUOTE=valkery;34255835]That is not what I am saying. I am saying that TNA, at least up until this point has not been found in nature.[/QUOTE] Which is irrelevant to a discussion of previous conditions which are theoretically sound.
[QUOTE=valkery;34252119]The wikipedia article and the fifth link both explicetly state that TNA has to be synthesised. I don't think it was present at the forming of life.[/QUOTE] Organic molecules came together to form a sort of shell, a very primitive cell membrane, which served as housing for very primitive molecules. This is very summarised. If you want, I can go quite indepth. We already know of the existence of several organic molecules outside Earth, so it's not so hard to believe.
It just the devil trying to deceive us, duh
[QUOTE=Motherfuckers;34255291][img]http://www.wicked-vision.com/images_rv/E/Evolution_cover.jpg[/img][/QUOTE] Don't worry guys, I got this covered. [IMG]http://styletips101.com/wp-content/uploads/2008/10/hs.jpg[/IMG]
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