Re: On influencing factors

Mon, 2 Nov 1998 11:35:16 -0500 (EST)

Subject: Re: On influencing factors
Date: Mon, 2 Nov 1998 11:35:16 -0500 (EST)

On Sun, 1 Nov 98 14:35:00 -0600 Mark Mills <>

Regarding gene expression

> I'm not sure what you mean by
> 'extreme environmental conditions,' though.

Waddington would do things like heat up fly embryos or blow ether over
them and see how this altered their development. The idea was that
gene expression was altered by these environmental insults. Often the
resulting phenotypes were quite similar to genetic mutant phenotypes,
in which case they were known as 'phenocopies'. This is not a
particularly fashionable line of research nowadays, although there are
some poor fools who are still at it (eg. Gatherer and Woodland 1996).

> 'Extreme' suggests 'abnormal,' and that's not my interest. I'm
> interested in common next neighbor interactions. My interest is this:
> to what degree is gene expression in one cell triggered by the behavior
> of neighboring cells.

Well, lots. See Hancock (1997).

> I hope you see the parallels for memetics.

I can see the analogy, but I'm not sure it's a helpful one, because the
mechanisms by which these neighbour interactions occur are very
different. I'm not sure that signal transduction research can tell us
much that would be applicable to memetics.

> I suspect many will be a bit uncomfortable with extra-cellular genetic
> triggers. Such a phenomena would diffuse the locus of control and cause
> a variety of philosophical problems.

I think I'm lost here. Development is controlled genetically. There
are differences between the ways that so-called mosaic embryos (eg.
molluscs, the most extreme case) and regulative embryos (mammals are the
archetypal example) implement the genetic blueprint. The fact that
cells signal to each other during development doesn't cause any
problems for this paradigm.

I might say in passing that developmental biology has had 3 or 4
paradigms in the 20th century. In consecutive order they are the
entelechy paradigm (Driesch 1880s), the mechanistic paradigm (Roux,
also 1880s). Roux won that argument, but then the pendulum swung back
a little towards Driesch with the organiser/field paradigm (Spemann
1920s). This gradually gave way to the biochemical paradigm (focussing
on things like redox gradients and metabolic activity and associated
with Needham, Waddington and Child among others 1930s) and finally the
molecular genetic paradigm which began with Eric Davidson and
colleagues at CalTech in the mid 1960s. The Nusslein-Volhard/Wieshause
Nobel Prize in 1996 was seen as a vindication of this approach (Spemann
was the last developmental biologist to get the Nobel, and the
feeling in the field was that it had been a long time in coming back).

Ironically much of the Spemann school's work has been reasessed in
molecular terms and found to be quite compatible with them (eg.
Gurdon, Melton, deRobertis, Harland and a host of other contemporary
giants). The biochemical school by comparison is now virtually
ignored. If you read a dev. biol. review paper it is often striking
how there will be references to papers from the 1920s to the 1940s
but then nothing again until the 1970s or even 1980s. A good example
of Kuhn's model of science.

Gatherer D and Woodland HR (1996) N-acetyl-cysteine produces late
respecification of the axis in Xenopus embryos. Developmental Dynamics
52, 165-177.
Hancock JT (1997) Cell Signalling. Longman, London.

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