disarray of embryology

Richard Gordon gordonr at cc.UManitoba.CA
Mon Jan 2 02:34:06 EST 1995


Dear Mark,
You asked me to justify my remark about the disarray of embryology. Let's=
=20
take Drosophila, your beast. It starts out with a maternal gradient, on=20
which, I gather, all explanations of what ensues depend. Here's a quote fro=
m:

Akam, M.E. & R. Dawes (1992). Insect segmentation: More than one way to=20
slice an egg. Current Biol.  2(8), 395-398.=20

"In Schistocerca  [the African desert locust], a fully-formed embryo can=20
be generated in an isolated posterior half egg. Maternal factors appear=20
to define where the embryonic primordium will form, and may define its=20
polarity, but appear to play little or no further role in patterning the=20
embryo ({Sander, 1976}). Indeed, in these lower insects the germ-line=20
derived nurse cells that synthesize the bicoid  and nanos  determinants=20
of Drosophila  are simply not present ({Mahowald, 1972}). In the ovaries=20
of these insects, only the oocyte nucleus is available to provision the=20
egg with maternal RNA.

"Even among the endopterygote insects, the requirement for maternal=20
information can be eliminated.... For example, in [the parasitic wasp]=20
Ageniaspis  the egg is small and contains little yolk. It undergoes=20
complete cleavage, to yield a loosely-packed ball of cells that resembles=
=20
the mammalian morula. As cleavage continues, the morula falls apart into=20
as many as 400 separate clusters of cells, each of which then organizes=20
itself into a separate embryo ({Martin, 1914}, reviewed in=20
{Ivanova-Kasas, 1972}). It is hard to believe that localized maternal=20
information has much of a role in the generation of pattern in this=20
embryo"=CA({Akam & Dawes, 1992}).

Am I really to believe that Drosophila provides a model for development,=20
when it can't even be applied to other insects, even the closely related=20
wasps? To me, that's disarray.

Best regards, -Dick Gordon, U. Manitoba[Jan1,95]

On Sun, 25 Dec 1994, Mark D. Garfinkel wrote:
>...=20
> =09Now Dr. Gordon's comment about "total disarray" is quite mysterious
> to me. You seem to imply that, to you as an "outsider", the developmental
> biology field appears to have generally confused hypothesis with experime=
nt,
> in order to promote certain popular models. Would you please elaborate?
>=20
> Mark
> --=20
> Mark D. Garfinkel (e-mail: garfinkl at iitmax.acc.iit.edu)
> My views are my own, which is why they're copyright 1994 (c)
> I post from here only because of miscellaneous news problems there.
>=20
>=20



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