rain forest ant-spore neurobiology

Michelle Anne Freeman maf2d at galen.med.Virginia.EDU
Wed Nov 24 05:15:04 EST 1993


ld231782 at parry.lance.colostate.edu  writes:

> I also saw a special on ABC recently called `the hidden world' or something 
> like that of an amazing fungus-spore-organism that appears in ordinary 
> backyards.  the spores collect at one stage in life and actually migrate
> in an oozelike fashion. Then they `bud' or `sprout' upon each other, with
> lower ones drying up and hardening for others to advance upon. Then this
> eventually `buds' into armlike projections that passing insects (the whole
> thing is totally microscopic) brush off on, as I recall.

I believe the organism you are referring to is the cellular
slime mold, Dictyostelium.  We learned a little bit about it in
my cell biology class a few years ago, because they are an
interesting model system for studying cell-cell interactions.
That is, what are the signals from one single amoeboid slime
mold cell crawling around in the dirt to another one (and
oodles more) that it's time to get together and have a party?
In 1989, when I took this class, it seemed that cyclic AMP (a
common messenger used in all cells) was secreted by these slime
mold cells (maybe the ones who were initiating the whole
bizarre event of forming the mold-fountain); other cells in the
nearby dirt would detect this somehow and migrate toward the
secreting cells, and be stimulated to also secrete cAMP. 
As more and more cells aggregated and secreted cAMP, a gradient
would form in the soil, and the amplified signal would be able
to recruit more cells from farther away.  From a cell biology
standpoint, the _transduction_ of this signal--i.e. what is the
cAMP altering in the cells so that they change direction,
change their secretion, change their morphology, change their
adhesiveness for each other, etc.?  Also what kinds of proteins
mediate this cell-cell adhesion?  (This may seem bizarre to
want to know these things about a stupid slime mold, but it has
application beyond mold zoology.  We know that biology has been
pretty conservative with a lot of its nifty inventions, and it
is likely that some of the same proteins involved in signal
transduction, adhesion, etc. in Dictyostelium are very similar
to proteins that do similar things in a different context in
humans.  Understanding how adhesion and migration are regulated
at a cellular level can provide outstanding insights into
malignancy--in metastatic cancer cells, one of the key features
(indeed _requirements) is disruption of cell-cell adhesion and
altered migration.)

> 
> I wonder if there are any books on `bizarre life forms' -- all of this
> is so unusual as to seem alien. They show how many of our categories -- 
> `worms, parasites, virus, bacteria, plant, animal' etc. are not so
> clear-cut as we would like to imagine. In fact the boundary between
> life and non-life is increasingly blurred itself.
> 

Where on earth did you get the idea that biology is clear-cut?
The way I see it, _all_ life forms are bizarre, if
you take the time to look at them.  You book would be a catalog
of all life.  "Unusual" life cycles--where the organism has a
limited set of hosts or environments--are but one facet.  You
probably hear about human parasites more than others (self-
centered-species that we are!), but even for a lot of these, we
are but one intermediate in its life cycle.  For example,
schistosomes (another trematode; also called "flukes") live
their adult lives and lay eggs in humans.  But the eggs
actually hatch in water, and the "larval" from (miracidium) has
to seek out a specific type of snail to mature into the
cercariae which actually infect humans; these cercariae then
mature in the human host into egg-laying adults.  One of the
ways that epidemics of schistosomiasis have been (tried to be)
controlled is by using molluscicides to kill the intermediate
snail host.

If you have boundary anxiety re: life vs. non-life, ponder the
boundary between self and non-self.  Do you consider the 
E. Coli that live in your intestine to be "not me"?  Yet, the
only humans who would not have bacteria as symbionts are people
who were placed in sterile "bubbles" at birth and remained
there.  They do important things for us just as much as our own
cells do:  they secrete vitamin K, essential to us for
clotting; they protect us from other more harmful organisms
(many times patients on antibiotics wind up with a bad
intestinal infection with Clostridium difficile; when their own
gut bacteria are killed by the antibiotic, C. difficile takes
over).  Another fun thing to think about is something that I
read in Lewis Thomas's _The Lives of a Cell_--we usually think
of viruses as nasty little not-quite-living-things that give us
colds.  But they may have served a very important evolutionary
role in carting genes around (he makes the analogy to
butterflies cross-pollenating flowers)--some viruses can
incorporate into the DNA of a cell, then when it hops out,
carry a part of that cell's DNA with it; when it then infects
another cell (maybe of a different organism), it can
incorporate into the DNA, and when it hops out, leave part of
it behind, and presto--one cell has now obtained a gene from
another cell, without any direct contact (i.e. no sex).  In
fact, phage (bacterial viruses) do this a lot.

I have another idea for a category for your "bizarre life
forms" book: defense mechanisms (another favorite of public TV
specials, I might add..)  Sea cucumbers squirt their guts out
onto their attackers!!!  Truly bizarre to me, but maybe more
subtle, are the creatures that make toxins that have come to be 
researchers' favorite pharmacological tools.  There are many organisms
that have figured out how to make an organic compound that
selectively targets an essential enzyme in its prey (e.g.
tetrodotoxin, made by puffer fish, blocks voltage-gated 
sodium channels, and thereby paralyzes its prey (or
unsuspecting sushi-eaters!).  One of the diatoms [a one-celled
ocean creature with silica shells] that causes red tide makes a
toxin--okadaic acid--that has been very useful in our lab because 
it selectively inhibits protein phosphatases.)  
If you look at the molecular structures of these toxins, it's like
looking at an architecture plan for the world trade center or
something.  We're talking complicated.  The world's best
organic chemists can't make 'em--how in the hell do these
things do it????!  BiZARRE!

I wish I knew the name of my zoology textbook from my
undergraduate "animal diversity" course, but I don't.  Actually
it was more the course than the textbook itself that was really
cool.  Cnidarians, Ctenophores, and Onychophorans were three
groups of organisms that I remember being intrigued by,
although the first 2 may be just because of the silent 'c' at
the beginning of their names; I think they also glow in the
dark or something.  Onychophorans are really interesting
creatures to me because they've been such an enigma to
evolutionary biologists; they're kinda worm-like thingys
(they're even called "velvet worms"), but not related enough to
worms to be placed in the same phylum--they get one all to
themselves.  They also do some things that were pretty advanced
for such a squishy looking thing, although I can't remember
exactly what.

Sorry for such a long post--I didn't realize I was marveling
at biology for so long until I just went back and re-read what
I wrote.  It's hard not to be enthusiastic!


-- 
Michelle Freeman				 o o
Neurosciences Graduate Student			\   /------
maf2d at galen.med.virginia.edu			|\_/|-\--
						|   |  \    
(And even though I'm a neuroscience student, 
I don't know a thing about ant nervous systems!  Sorry...)
--
Michelle Freeman				 o o
Neurosciences Graduate Student			\   /------
maf2d at galen.med.virginia.edu			|\_/|-\--
						|   |  \    



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