Did tissues arise from other cells or cell differentiation?

[icakeov]

Hi I have a pretty specific question.

It is in regards to tissues in multicellular organisms.

Is there any information on how different cell grouping arose in multicellular organisms?

I have some ideas from what I've so far read and learned:

- Would this have happened because two different types of cells "met" and decided to collaborate? This would be similar to the mitochondria example, the difference being of course, that mitochondria retained their DNA. In this scenario, the two cell types would have had to somehow share their reproductive cell's DNA.

An extension to this question: if this indeed might have been what happened, then, would it have happened at the stages when all cells were still multicellular, or would it have been somehow possible to have two multicellular organisms to "meet" and have their reproductive cells mix DNA. (This seems unlikely to me)

- Another scenario would be that that a a multicellular organism that would have initially been consisted of only the same cells started having specific gene mutations in the reproductive cells. These new genes would then start coding for a bit different types of cells in one area of the organism. For example, if certain cell mutation would have ended making them absorb nutrients more efficiently than the cells on the other side of the organism? And same for waste removal. And then we're of to the races. I guess this goes along with the concept of stem cell, cell differentiation and epigenetics, so I am more inclined this might be the more accurate picture.

Any feedback would be welcome! :)

 

[Simon Bridge]

This is an area of speculation - what we are looking for are plausible paths that evolution may have taken in order to examine rules for organisms now and to the future. Coming up with ideas is easy - the trick is testing them.

iirc the usual pathways go along the lines of colony organisms of single-celled organisms become more and more interdependent.

 

[icakeov]

Here is a great video that talks about this subject. But right at the time that I indicated, it says "but their existence became linked".


That's the part that confuses me. How did it become linked?

To be specific, if the nucleus has its own DNA and chloroplasts and mitochondria have their own, and they are separate like that, how does the multicellular eukaryotic organism replicate? Do sperm cells carry their DNA separately? Or do sperm cells somehow “carry” the information in their nucleus for them. If it’s the latter, how on Earth did this come about?

 

[Simon Bridge]

Starting from already having lots of single celled organisms that are not multi-walled ... they live by a variety of means, one of which will involve eating other organisms. If one eats another, but cannot "digest" it, you have a multi-walled organism ... probably short lived OK, but the longer lived ones are more likely to continue in a semi-parasitic/semi-interdependent way. Getting their reproduction in sync, so to speak, would be a major advantage.

Note: sperm cells only carry chromosomes from the nucleus.

 

[icakeov]

Thanks for your response!
Right, so somehow, they nucleus of the main cell managed to have the rest of the DNA into it?
That's the step that I am curious about. How would that have happened?
Once the sperm cell fertilizes the egg cell, then these stem cells (I presume) start creating new cells that will contain both chloroplasts and/or mitochondria?

 

[Simon Bridge]

Right, so somehow, they nucleus of the main cell managed to have the rest of the DNA into it?

No. That is the opposite of what I said.

http://scienceline.ucsb.edu/getkey.php?key=3242

 

[Simon Bridge]

I just checked my facts before continuing since this is outside my field.
The gametes (egg and sperm) are eukaryote cells too, just with half the chromosomes in their nuclei but a full set of chromosomes in their organelles^*, like the mitochondria. At fertilization, the egg destroys or otherwise absorbs the sperm's organelles ... this is why it is possible to use DNA to trace origins through the female but not the male lines. The various organelles reproduce themselves within the cell and get passed around as the cell divides.

https://en.wikipedia.org/wiki/Paternal_mtDNA_transmission
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC19448/

[*] guessing - I only checked for mitochondria.

 

[icakeov]

Fascinating! Thanks so much for the information and helping find extra links.
So basically, mitochondria divides through fission and looks like the nucleus of the cell controls its rate of replication so it doesn't get out of hand and destroy the cell.

Now that the organelles functionality and replication is out of the way, I'm back to thinking about the post original focus. And that is, how does the cell in its nucleus create different tissues, that is, different types of cells? Or I guess different types of itself?
Guess: this was through slow mutation or mixing of different genes in the chromosomes through the millennia?

Thanks so much again!

 

[Simon Bridge]

Fascinating! Thanks so much for the information and helping find extra links.
So basically, mitochondria divides through fission and looks like the nucleus of the cell controls its rate of replication so it doesn't get out of hand and destroy the cell.

It's more like the cells are in equilibrium ... "control" tends to imply a conscious design element and we are trying to talk about evolution.

Now that the organelles functionality and replication is out of the way, I'm back to thinking about the post original focus. And that is, how does the cell in its nucleus create different tissues, that is, different types of cells? Or I guess different types of itself?
Guess: this was through slow mutation or mixing of different genes in the chromosomes through the millennia?

Oh you mean "how did tissue differentiation evolve from primitive cells?"

You can see likely pathways by examining colony organisms... especially those where the component single-cells are variations on the same blueprint. I'm thinking Portugese Man of War but there are probably better examples.

If you think of a blob of replicators floating about in something - the colony grows until food and oxygen cannot reach the middle and the ones there die off. Bacteria colonies are like this: the middle is dead ...

Just taking a single example of a possibility to start your imagination down a useful line:
It is more useful to have the dead ones on the ioutside where they can protect the colony.
Colony's which shove the dead stuff to the outside they will grow a skin ... but some cells are better at growing the kind of dead cell that makes a defensive wall so... now you have specialist skin cells and an eliminatory system. In this early proto multi-cellular organism does not have cooperating parts you understand, they just have cells which pass nasty stuff one way and good stuff the other way. A similar approach to food and oxygen results in regularly traversed pathways like game-trails so you get tubes, and cells that are good at being tube walls, and cells that are good at shoving things about and proto-organs have emerged.

In this proto-creature, all it's cells are sort of but not exactly stem cells - shifting for circumstance.

This is an active field of study BTW:
http://www.mcb.arizona.edu/research/differentiation-development-and-evolution
http://www.ncbi.nlm.nih.gov/books/NBK10031/

 

[icakeov]

Great! That's super helpful! Thank you so much Simon!