Re: News: Humans and sponges may share a slimy ancestor

"Lorentz" <drosen0000@xxxxxxxxx> wrote:
On Feb 3, 2:23=A0pm, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:
"Lorentz" <drosen0...@xxxxxxxxx> wrote:
On Jan 29, 4:04=3DA0pm, "Robert Karl Stonjek" <rston...@xxxxxxxxxxxxxx>
wrote:

If they're true, the findings have a difficult implication for many
biologists: they suggest that the nervous system evolved twice in two
separate systems. Placozoa and sponges don't have a nervous system, bu=
t t=3D
he
related cnidarians - which include jellyfish - do.

=A0 =A0 I propose that the nervous system evolved once, but crossed
clades by horizontal gene transfer. Maybe the nervous system evolved
first in cnidarians, and crossed into the triblastic animals via a
virus. Or maybe the other way. A protocnidarian without a nervous eats
something with a nervous system and accidentally incorporates its DNA.
=A0 =A0 I would be interested if the genes coding for acetylcholine are
the same in all clades. Acetylcholine is a venom in cnidarians. It
stings because it is a neurohumor in higher forms of life.
Acetylcholine is a complicated protein.

Huh??? Acetylcholine is a small and simple molecule. Simpler than
adenine, similar to arginine, and certainly simpler than any proteins.
http://en.wikipedia.org/wiki/Acetylcholine

If cnidarians and humans share
the same neurohumors, then I would have to say that the nerve cell is
a primitive feature.

Both acetylcholine and the synthesizing
enzyme choline acetyltransferase could have been present
well before there were nervous systems. Metazoan cells
need to communicate chemically with their sibs, and they
use molecules like acetylcholine to do so even if evolution
(or development) has not yet generated nerve cells.
Okay. It wouldn't be conclusive. There is more than one way
to evolve a nerve cell. However, there are observations that could
falsify my hypothesis. It seems to me that if acetylcholine evolved
for different functions than use in nerve cells, there may be extant
organsisms that still use acetylcholine in a nerveless fashion.
1) Are there any unicellular organisms, any at all, that generate
acetylcholine to communicate (or anything else)?

Yes. (And most plants, too)
http://jeb.biologists.org/cgi/content/abstract/204/11/1901

-A natural bacterium that spits out acetylcholine would blow my
hypothesis away.

Bacteria also produce acetylcholine

Horiuchi et al.
Evolutional study on acetylcholine expression
Life Sciences
Volume 72, Issue 15, 28 February 2003, Pages 1745-1756

Excerpt from abstract: "These findings demonstrate the presence of ACh
and ACh-synthesizing activity in evolutionally primitive life as well as in
more complex multicellular organisms. In the context of the recent discovery
of non-neuronal ACh in various mammalian species, these findings suggest
that ACh been expressed in organisms from the beginning of life, functioning
as a local mediator as well as a neurotransmitter."

2) Are there any glands in multicellular organisms that generate
acetycholine, independent of the long dendritic cells that we call
nerves?
-A gland that spits out acetylcholine for long distance
communication would count against my hypothesis.
Come to think of it: The stinging cells in cnidarians aren't
nerves, but they still spit out acetylcholine. However, it seems to me
that such stinging cells could only be useful in a world where most
metazoans use nerve cells.

You may want to look at this paper

Ubiquitous expression of acetylcholine and its biological functions in
life forms without nervous systems
Kawashima et al.
Life Sciences
Volume 80, Issues 24-25, 30 May 2007, Pages 2206-2209
Proceedings of the 2nd International Symposium on Non-neuronal Acetylcholine

So not only are you wrong, but they have already held two international
symposia to discuss the fact that you are wrong. ;-)


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