Nerve Cell Clones
Richard S. Norman
rnorman at umich.edu
Mon Oct 7 19:26:14 EST 2002
On Mon, 07 Oct 2002 21:11:21 GMT, "Kevin Hertzberg"
<khertzberg at telia.com> wrote:
>From: "Dan Marquez" <dmarquez3 at socal.rr.com>
>Sent: Monday, October 07, 2002 9:51 PM
>Subject: Re: Nerve Cell Clones
>> I think this is exciting research. What I'm confused about is why such
>> cell research is so controversial! (Does anybody here understand why?)
>Correct me if I'm wrong (which is likely, because I'm not a scientist), but
>don't they have to grow stem cells in unborn babies?
>And the controversial matter if this is correct would of course be what to
>do with the foetus them stem cells is grown within.
>This is only what I've learned in biology in school, so as I said I'm not
>sure if I'm right.
Note: the phrase "unborn babies" is a rather loaded term. A baby is
not a baby until it is born. Before then, it is a zygote, an embryo,
or a fetus. This is a large part of the "controversy".
Stem cells are cells that have the ability to divide, and so act as a
source of new cells, and also the ability to differentiate into a
range of specific cell types, and so act to regenerate a complex
structure. The fertilized egg is called "totipotent" since it has
the ability of differentiating into all of the human cell types. Cells
that are only "multipotent"have the ability to become many different
things but not everything. For example, mesenchymal stem cells can
produce bone, muscle, cartilage, fat and other connective tissues, but
not nerve or muscle..
When a fertilized egg starts to divide, after five or six days it
forms an early embryo stage called the blastocyst. This consists of a
hollow mass of some 70 cells called the trophoblast that will turn
into the placenta and related structures. Inside, there are some 30
cells called the inner cell mass. These are called "pluripotent"
because they will produce all the cell types in the adult organism.
These are the cells all the talk is about, the embryonic stem cells
from the inner cell mass. These cells can NOT develop into a human
because they do not have the ability to form a placenta, an essential
organ for fetal existence, and hence for the production of a new
The blastocyst (embryo) at this stage is about 0.1 to 0.2 mm diameter
(1/200 inch). Blastocysts produced the normal way have not yet
embedded into the wall of the uterus. They are NOT fetuses, just a
mass of some 100 cells. I would not call them "unborn babies". In
fact, a tremendous number of such embryos simply fail to implant and
pass through the woman's system completely undetected. There is a
fertilization but no pregnancy at all. Blastocysts produced by
in-vitro fertilization are grown until this stage and then stored,
waiting for possible implantation. If they are not implanted, then
they are normally destroyed.
The controversy is whether, instead of destroying the unused
blastocyst, they could be used as a source of embryonic stem cells. At
no time in the process is a foetus every formed or used.
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