Are stem cells in any way representative of the eukaryote ancestral to metazoa?

Vivian on 29/11/2007 at 17:29

Hi,

I've been teaching evolutionary biology to kids these past couple of weeks, and while it seems I've forgotten most of what I used to know, I did have an interesting thought (i'm not a microbiologist, so excuse me if I am being grossly thick) - stem cells, they're basically single-celled organisms, right? I mean, they aren't differentiated, they lack any specialised structures that would make them a useful part of a multicellular animal, all they can do without some kind of clever chemical gradient prodding is absorb nutrients and reproduce (?). So, how much difference is there between different species/genus whatever's stem cells? Is there some kind of evo-devo thing going on here, similar to how embryological development mirrors some aspects of phylogenetic history? Do metazoan stem cells represent the single-celled ancestor of all metazoans?
Because that would be neat. I haven't done any poking around to see if this is a widely held theory or if I'm spouting bollocks, but I really like the idea. Any qualified people want to chip in?

The_Raven on 29/11/2007 at 17:50

No mention of dinosaurs in this thread. :(

SubJeff on 29/11/2007 at 18:48

Quote Posted by Vivian

So, how much difference is there between different species/genus whatever's stem cells?

How exactly do you mean? Apart from the obvious difference in the number of chromosomes and the different types of genes I suppose that different species' cell membranes and protoplasms will differ in the proteins expressed. Because there are different genes at play, and they are the fundamental building blocks, everything else will differ slightly but that difference in terms of function and potential is so massive as to be unfathomable.

Spaztick on 29/11/2007 at 19:47

LYKE DA STEM CELLZ R BAD OMG LULZ PLAYING GOD DINOSAURS EVOLUTION SCHOOL TEXT BOOK!1!!11

Pyrian on 29/11/2007 at 19:58

Of course the DNA set is going to depend completely on the originating species. In turn, this means that the receptor proteins on its surface are going to vary, quite possibly widely, although I suspect they're pretty similar among, say, mammals (we all have skin, muscle, bone, etc.). Internally, though, yeah, they've all just got the basic cellular machinery. If anything, they're probably simpler than any ancient single-celled counterparts: they don't have to digest, they really do expect their nutrients to be fed to them by a loving host body.

It's worth noting that embryonic development loosely mirrors ancestral forms. Basically, we all start off as tadpoles.

The_Raven on 29/11/2007 at 20:49

I wish one of the embryonic development stages mirrored the trilobite.

Pyrian on 29/11/2007 at 20:51

Quote Posted by The_Raven

I wish one of the embryonic development stages mirrored the trilobite.

Might've, if we evolved from them. Back then, what became vertebrates were represented by a small worm.

SubJeff on 29/11/2007 at 20:52

Quote Posted by The_Raven

I wish one of the embryonic development stages mirrored the trilobite.

Yours probably did.

Oh zing* :p

Vivian on 29/11/2007 at 21:56

I guess you're right - variable chromosome number, membrane structure etc, stem cells aren't going to be all that similar across taxa (seems obvious, now you mention it. Duh). But how far is a stem cell from being a 'typical' unicellular eukaryote, if there is such a thing? Is it any closer than any other of the less-complex somatic cells? (i.e. not wierd things like muscle or nerves).

demagogue on 29/11/2007 at 22:19

Armchair science ... great!
(You weren't serious about the "qualified" part were you?)

Even though a stem cell is undifferentiated compared to organ cells, doesn't it still have a pretty defined function based on what proteins it's going to be making? (I guess Pyrian already said this).

Also I've been waiting for the next time to quote this: "Ontogeny recapitulates phylogeny." (already said, though.)

Third, my contribution, I was reading about hybrid species not to long ago, and this question occurred to me, well, not exactly your question, but in the ballpark ... how does a stem cell work for a hybrid? It's sort of doing cross-duty in something it wasn't exactly designed for, but it can pull it off ... and granted it isn't acting like its counterpart millions of years down the tree, but a little ways down. It can get the job done.

Actually, the hybrid I was reading about was human, the theory about when hominids split from apes because of the problem that hominid fossils seemed to start before ape dna ended, they reconciled it by thinking that the early hominids that eventually turned into us were actually a hybrid species between apes and the "real" humans that later died out. (I have to say, btw, I got a kick out of the theory; wouldn't some quarters of society love to learn that we are literally monkey-men hybrids, and the real humans abandoned us long ago.) But, anyway, if that's right, there's a case study for your question.