Re: the liver and the brain

From: r norman (rsn__at__comcast.net)
Date: 09/06/04 

Date: Sun, 05 Sep 2004 23:43:23 -0400

On Sun, 05 Sep 2004 21:05:51 -0400, Wolf Kirchmeir
<wwolfkir@sympatico.ca> wrote:

>Yes, I just love C. elegans. Especially the fact that it needs 300
>neurons but only 81 muscle cells. Lovely! Brain over brawn very time,
>eh? :-)
>
>Question: Are there any environmental factors whose presence or absence
>disrupt or divert development? Any non-lethal ones? Are there any
>environmental factors whose presence/absence affects the timing of
>development? I suspect there are, but I would like to know one way or
>the other. I'm not asking about the obvious ones, such as water, without
>which the creature will die. Anther way of asking the question is,
>What's the range of, e.g., pH, etc in a normal environment for this
>worm? Any differences at either extreme? Etc.

Neither development nor C. elegans are in my area, so I only know some
generalities. The major feature is that environmental cues such as
pheromones or high temperature (27 C) can trigger a resting stage in
larval development, the Dauer stage or diapause.

Of course, development in any one cell is always influenced by
"external" factors derived from other cells in the neighborhood. , So
for the nervous system in particular, migration of cells, axonal
growth and synaptic development depend on the proper "environmental"
cues. In this sense, the environment is everything outside the
specific cell under consideration. Still, the signals are chemical and
chemicals in the external environment clearly will cause abnormal
development by disrupting the normal cell signaling mechanisms that
regulate gene transcription and expression. In particular, a wide
variety of mutagens, hormones, and pharmacological agents can modestly
or drastically affect development. In fact, using a drug that blocks
a particular protein is the usual way of testing whether that protein
plays a role. Unlike the Dauer stage which is a natural occurrence,
these are highly artificial environmental modifications.

Also, C. elegans is capable of associative learning, context specific
habituation, and other plastic changes in behavior. This is not
development, but does illustrate that an animal that is so highly
constrained genetically also shows a learned component to its normal
behavior.

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