4 ms·

Why almost all multicellular organisms begin life as a single cell

77 points by llambda 15y ago

jessriedel 15y ago
Isn't this kind of a confused presentation? (I'm talking about the popular article, of course; I have no doubt the researchers know their stuff.) The cells of multi-cellular organisms like whales and humans aren't just cooperative, they are genetically identical, which means their evolutionary prospects are tied together. The DNA in a pancreas cell is the same DNA as in a sperm cell, so it's "in the pancreas cell's interest" to help out the body. (Really, the key idea is the evolution is a competition between the bits stored in DNA, not the physical DNA itself.) And the root reason the cells of multi-cellular organisms like whales and humans are identical is because of sexual reproduction. So the key bottleneck isn't the one-ness of the one cell, it's the genetic identical-ness. Now, yes, once you say all that I guess you can say that the mutations in animal cells leading to non-cooperative behavior (i.e. cancer) are evidence of this 100-division limit. But the amoebae are qualitatively very different since they aren't all genetically identical. It's really closer to the cooperation between human * families* than human cells, isn't it?
- jacquesm 15y ago
  > The cells of multi-cellular organisms like whales and humans aren't just cooperative, they are genetically identical http://www.sciencedaily.com/releases/2009/07/090715131449.htm http://www.sciencedaily.com/releases/2009/07/090715131449.ht...
  - civilian 15y ago
    The article didn't explain the genetic difference very well... can you provide an explanation?
    - pygy_ 15y ago
      They found out that the pathogenic mutation was only present in vascular tissue, but not in blood cells. DNA replication errors occur all the time, even in multi-cellular organisms. Some of them lead to cancer, but most of them are either lethal (for the cell), or, most of the time, innocuous. The most likely scenario for the abdominal aortic aneurism is the following: A mutation can occur during organogenesis, in utero. The earlier it occurs, the more cells will be affected. Said mutation can be initially benign, but become problematic in the long run. If the mutation occurs after the differentiation between fibroblasts and blood progenitor cells, only affecting the former, you get the scenario described in the ScienceDaily article.
- pygy_ 15y ago
  > The cells of multi-cellular organisms [...] are genetically identical Nope. As stated in another comment, somatic mutations occur all the time, leading to slight diffenrences between the cells of a given multi-cellular organism. Most of them are insignificant, though.
gwillen 15y ago
I just skimmed this article, but it doesn't appear to make the interesting point that came to my mind when reading it, which is: in a multicellular organism, what the article calls a "cheater", we call a "cancer". A "cheater" is just a cell which, despite its common origin, has mutated to compete with the other cells instead of cooperate with them. And indeed, we see cells do that; we also see adaptations -- the tumor suppressor genes -- specifically designed to inhibit such cells.
- jcitme 15y ago
  I came away with the opposite conclusion: "If amoebae occur in well-mixed cosmopolitan groups, then cheaters will always be able to thrive by freeloading on their cooperative neighbors. But if groups derive from a single cell, cheaters will usually occur in all-cheater groups and will have no cooperators to exploit. The only exceptions are brand new cheater mutants in all-cooperator groups, and these could pose a problem if the mutation rate is high enough and there are many cells in the group to mutate. In fact, the scientists calculated just how many times amoebae that arose from a single cell can safely divide before cooperation degenerates into a free-for-all. The answer turns out to be 100 generations or more. So population bottlenecks that kill off diversity and restart the population from a single cell are powerful stabilizers of cellular cooperation, the scientists conclude. In other words our liver, blood and bone cells help our eggs and sperm pass on their genes because we passed through a single-cell bottleneck at the moment of conception." If anything, I felt this section was /strongly/ hinting at cancer in a group of cells. Rereading it, though, it seems that there is nothing explicit in here, so I'm not sure what caused me to spawn this thought process. Anyways, this article felt like solid scientific reporting, without too many 'guesses' into this application of this into cancer, like pop science nowadays.

77 points by llambda 15y ago

Isn't this kind of a confused presentation? (I'm talking about the popular article, of course; I have no doubt the researchers know their stuff.) The cells of multi-cellular organisms like whales and humans aren't just cooperative, they are genetically identical, which means their evolutionary prospects are tied together. The DNA in a pancreas cell is the same DNA as in a sperm cell, so it's "in the pancreas cell's interest" to help out the body. (Really, the key idea is the evolution is a competition between the bits stored in DNA, not the physical DNA itself.) And the root reason the cells of multi-cellular organisms like whales and humans are identical is because of sexual reproduction. So the key bottleneck isn't the one-ness of the one cell, it's the genetic identical-ness. Now, yes, once you say all that I guess you can say that the mutations in animal cells leading to non-cooperative behavior (i.e. cancer) are evidence of this 100-division limit. But the amoebae are qualitatively very different since they aren't all genetically identical. It's really closer to the cooperation between human * families* than human cells, isn't it?

jacquesm 15y ago
> The cells of multi-cellular organisms like whales and humans aren't just cooperative, they are genetically identical http://www.sciencedaily.com/releases/2009/07/090715131449.htm http://www.sciencedaily.com/releases/2009/07/090715131449.ht...
- civilian 15y ago
  The article didn't explain the genetic difference very well... can you provide an explanation?
  - pygy_ 15y ago
    They found out that the pathogenic mutation was only present in vascular tissue, but not in blood cells. DNA replication errors occur all the time, even in multi-cellular organisms. Some of them lead to cancer, but most of them are either lethal (for the cell), or, most of the time, innocuous. The most likely scenario for the abdominal aortic aneurism is the following: A mutation can occur during organogenesis, in utero. The earlier it occurs, the more cells will be affected. Said mutation can be initially benign, but become problematic in the long run. If the mutation occurs after the differentiation between fibroblasts and blood progenitor cells, only affecting the former, you get the scenario described in the ScienceDaily article.
pygy_ 15y ago
> The cells of multi-cellular organisms [...] are genetically identical Nope. As stated in another comment, somatic mutations occur all the time, leading to slight diffenrences between the cells of a given multi-cellular organism. Most of them are insignificant, though.

gwillen 15y ago

I just skimmed this article, but it doesn't appear to make the interesting point that came to my mind when reading it, which is: in a multicellular organism, what the article calls a "cheater", we call a "cancer". A "cheater" is just a cell which, despite its common origin, has mutated to compete with the other cells instead of cooperate with them. And indeed, we see cells do that; we also see adaptations -- the tumor suppressor genes -- specifically designed to inhibit such cells.

jcitme 15y ago
I came away with the opposite conclusion: "If amoebae occur in well-mixed cosmopolitan groups, then cheaters will always be able to thrive by freeloading on their cooperative neighbors. But if groups derive from a single cell, cheaters will usually occur in all-cheater groups and will have no cooperators to exploit. The only exceptions are brand new cheater mutants in all-cooperator groups, and these could pose a problem if the mutation rate is high enough and there are many cells in the group to mutate. In fact, the scientists calculated just how many times amoebae that arose from a single cell can safely divide before cooperation degenerates into a free-for-all. The answer turns out to be 100 generations or more. So population bottlenecks that kill off diversity and restart the population from a single cell are powerful stabilizers of cellular cooperation, the scientists conclude. In other words our liver, blood and bone cells help our eggs and sperm pass on their genes because we passed through a single-cell bottleneck at the moment of conception." If anything, I felt this section was /strongly/ hinting at cancer in a group of cells. Rereading it, though, it seems that there is nothing explicit in here, so I'm not sure what caused me to spawn this thought process. Anyways, this article felt like solid scientific reporting, without too many 'guesses' into this application of this into cancer, like pop science nowadays.