Multicellularity and specialised lineage cells

[thorium1010]

So the question is even though we may have some fair idea how multicellularity came about. How would this lead onto specialized line-aged cells in a multicellular organism ? For example differentiating to blood cells or bone cells.

http://en.wikipedia.org/wiki/Multicellular_organism

 

[bobze]

Hey Thorium,

This is a good question and a very complex one. I don't think there is a for sure answer, but there is some good ideas. The first place to start I think, isn't with cells but rather with insects.

The question is then, why are there "specialized" bees in a bee hive that forgo their chance at reproduction?

The answer is in the genetics. It turns out, at least in social insects, that they get along so great and "accept their place" because they are so closely related together. Or as Haldane phrased it; "I would lay down my life for two brothers or eight cousins".

Meaning that, as far as evolution is "concerned" its okay for you to sacrifice yourself for an equal amount of hereditary material that can still be passed on. I suspect in early multicellular organisms it wasn't much different--Where it is okay for reproductive cells to specialize in just that while other cells provide support for those reproductive cells.

In a way, none of that has actually changed--The only thing that has, is the functions of the other cells, which have become more specialized through evolution to support those reproductive cells. In that way, at least a simplified way, you could really describe all the rest of our bodies as "support" cells for those reproductive cells. I think to answer your exact question though, you'd have to be specific. Cell lineage specialization evolve to solve environmental problems. For instance, as multicellular colonies grew larger and larger diffusion would have been no long sufficient to supply cells with nutrients. A vascular system and corresponding cells would need to evolve to solve this problem.

Some specialized cell lineages we seem to know quite a bit about--Others not so much. Its something you'd have to look into and would require considerable reading. Some specific specializations are touched on in more advanced biology textbooks, Like The Cell, IIRC. Another good book to try might be Strickberger's evolution: the integration of genes, organisms and populations or other high level EvoDevo books.

 

[Pythagorean]

I've always been intrigued with multicelluarity. One organism that might be interesting in this context is the slime mold:

 

[Biosyn]

I've found this article in bookmarked some time ago in my browser.

It's about using yeast to investigate how multi-cellularity came about.

http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001122

 

[thorium1010]

Hey Thorium,

This is a good question and a very complex one. I don't think there is a for sure answer, but there is some good ideas. The first place to start I think, isn't with cells but rather with insects.

Meaning that, as far as evolution is "concerned" its okay for you to sacrifice yourself for an equal amount of hereditary material that can still be passed on. I suspect in early multicellular organisms it wasn't much different--Where it is okay for reproductive cells to specialize in just that while other cells provide support for those reproductive cells.

In a way, none of that has actually changed--The only thing that has, is the functions of the other cells, which have become more specialized through evolution to support those reproductive cells. In that way, at least a simplified way, you could really describe all the rest of our bodies as "support" cells for those reproductive cells.


I think to answer your exact question though, you'd have to be specific. Cell lineage specialization evolve to solve environmental problems. For instance, as multicellular colonies grew larger and larger diffusion would have been no long sufficient to supply cells with nutrients. A vascular system and corresponding cells would need to evolve to solve this problem.

Thanks bobze. So you are saying the differentiation into lineage cells was due to forging behaviours like larger good of all the cells and not by chance. But it would be difficult to explain how this would increase survival of the organism. unless the lineage cells were repaired (whenever damaged) and replaced their functioning would stop. I know there are stem cells.
Colony of daughter cells is not the same as lineage cells, because it comes with a price they have to be continuously repaired and replaced.wheraes a daughter cell is got by simply dividing in the existing cells.

 

[bobze]

Thanks bobze. So you are saying the differentiation into lineage cells was due to forging behaviours like larger good of all the cells and not by chance.

No I don't think changes like that would be due to chance, rather selection. If you look at examples of multicellularlity that arises in labs as it has on occasion, you see it often is a response to predation.

For instance see here.

But it would be difficult to explain how this would increase survival of the organism.

Remember what is evolving though, in the cases of multicellularlity and specialization (which arose multiple times) its changes in allele frequencies in a population living together.

unless the lineage cells were repaired (whenever damaged) and replaced their functioning would stop. I know there are stem cells.

Right, early on cells would still retain the ability to replace themselves, basically making cloned daughter cells (think of mitosis). When this whole "colony supports the reproductive cells" thing gets important though is when sex shows up on the scene. Then we have cells dedicated to reproduction: but in a very special way--a way that introduces new combinations of variation in progeny.

The evolution of sex then is important for the topic of the evolution of specialized lineages, in deed it wouldn't surprise me if this was one of the first or the first type of specialized lineage.

Colony of daughter cells is not the same as lineage cells, because it comes with a price they have to be continuously repaired and replaced.wheraes a daughter cell is got by simply dividing in the existing cells.

Right, but I think you might be thinking about it too fast. Its not like one day we had simple colonies of cells than, bam; complex multicellular organisms. I'm not sure how often cells need to be "replaced" in something like a volvox .

 

[mishrashubham]

Thanks bobze. So you are saying the differentiation into lineage cells was due to forging behaviours like larger good of all the cells and not by chance. But it would be difficult to explain how this would increase survival of the organism.

The key thing to note over here is that they are all genetically related.

 

[thorium1010]

Right, early on cells would still retain the ability to replace themselves, basically making cloned daughter cells (think of mitosis). When this whole "colony supports the reproductive cells" thing gets important though is when sex shows up on the scene. Then we have cells dedicated to reproduction: but in a very special way--a way that introduces new combinations of variation in progeny.

The evolution of sex then is important for the topic of the evolution of specialized lineages, in deed it wouldn't surprise me if this was one of the first or the first type of specialized lineage.

Thanks again. we know that reproduction(sexual reproduction ) is essentially a meiotic division. so was there any pressure or trait to develop cells with half the genetic material.Perhaps it had to develop long before. And even if there are cells with half the genetic material they need not fuse to form cell with the ability to form the multi cellular organism .Sorry ,this is all speculation i know, but the subject is interesting

 

[mishrashubham]

Thanks again. we know that reproduction(sexual reproduction ) is essentially a meiotic division. so was there any pressure or trait to develop cells with half the genetic material.Perhaps it had to develop long before. And even if there are cells with half the genetic material they need not fuse to form cell with the ability to form the multi cellular organism .Sorry ,this is all speculation i know, but the subject is interesting

We do have organisms with haplontic life cycles in which the haploid stage is dominant, mitosis occurs only in haploid condition. Diploid condition is not necessary for multicellularity. We even have polyploid organisms.
As for meisosis, you might want to look at this
http://www.genetics.org/content/181/1/3.full