Re: Count sheep, anyone?

Brian T. Greuel (
Wed, 05 Mar 1997 22:37:02 -0500

Loren Haarsma wrote:

> >>Here's a scenario which seems much more probable: using cloning
> >>techniques to grow fetal-like tissue for medical applications. Already,
> >>fetal tissue is being experimented with as a treatment for certain
> >>medical conditions (e.g. for re-growing damaged brain cells). It could
> >>be argued, medically, that the best tissue for this would be tissue with
> >>identical DNA to the patient. So, take DNA from one of the patient's
> >>cells, treat it and insert it into an ennucleated donated human egg
> >>cell, induce it to start dividing, grow it in vitro for a while, and
> >>transplant the appropriate cells back into the patient.

In the recently reported cloning experiments with sheep, a nucleus (not
purified DNA) was introduced into an enucleated egg. What made this
work so remarkable was that the nucleus was taken from an adult sheep
cell (i.e. udder cell) that was highly differentiated. Somehow in the
context of the egg cytoplasm the nucleus was "reactivated" to express
embryonic genes and begin the process of development. A similar feat
had been accomplished in amphibians, but no one thought it was possible
for mammals. Cloning of mammalian embryos by nuclear transfer from
cleavage-stage embryonic cells had been achieved earlier, but it did not
captivate the imagination of the media like the recent work. And, of
course, bisecting early cleavage-stage embryos has led to "twinning" of
mammalian embryos, including "spare" human embryos generated by in vitro

>1. One way to do in vitro screening for fatal genetic abnormalities is
>to allow the fertilized egg to grow in vitro to the eight-cell
>blastomere stage, remove two cells, and screen them.

You must mean eight-cell embryo (or eight-blastomere embryo) stage. The
words "cell" and "blastomere" are equivalent for the cleavage stage of

> 2. Back to cloning. It is entirely possible that the procedure
> postulated at the beginning of this letter could be modified a bit so
> that it would *not* be possible for this procedure to produce a viable
> embryo. (One "crude" way would be to include a retrovirus with the
> donated DNA which would interrupt the normal developmental program at
> some stage. There are probably subtler ways to accomplish this.) Would
> this alter the procedure's moral status?

If I recall correctly, retroviruses are not transcriptionally active in
early embryos. At what point are you proposing terminating
development? In the final analysis, what is the real difference between
genetically programming a termination of human development and just
destroying the human embryo outright?

Brian Greuel