This page is still under construction
3rd June 1998
Gap Junctions
These are protein structures which allow cells to communicate. When gap
junctions are present in a late stage 8-cell mouse embryo, it is possible
to inject dye into one cell and then to see the dye spread throughout all
the other cells. The dye is able to pass through the gap junctions. It
is thought that these junctions allow cells to pass signals to each other.
This communication may be important for the developmental fate of the embryo,
whereby absence of or poorly communicating gap junctions may lead to developmental
arrest.There have recently been reports on gap junctions in human embryos.
One report found little evidence of gap junction presence in human embryos,
even up to the blastocyst stage. This study relied on spare embryos from
a fertility programme, so may have been biased by the selection of the
worst embryos. The more recent report, still relied on spare embryos, but
because this programme did not routinely freeze spare embryos, their quality
may have been somewhat superior to the former study.In the more recent
study, gap junctions were found in 8-cell human embryos, but often in a
disordered state. Only one or two embryos demonstrated well ordered gap
junction presence and consequently the ability to compact. Compaction is
a state during which cell-cell communication is at its best, as each cell
maximises its contact with its adjacent neighbours. My own research has
shown a definite link between ordered gap junction presence, compaction
and embryo viability. In fact, many years ago, a brief report of mine was
published in the Journal of IVF, where I noted the fact that spare human
embryos in my fertility programme, did not compact properly. Indeed, they
even resembled the embryos from a particular infertile mouse strain that
I had also worked on.I am happy to speculate that gap junctions play a
crucial role in embryo viability. Furthermore, I believe that the vast
majority of human embryos derived from infertility patients, suffer from
disordered gap junction distribution, which therefore renders them inviable,
thereby explaining the difficulty in achieving pregnancy.
Human cloning
Human cloning is still some way off. Not least because many countries which
might pioneer the method have opted for a blanket ban or moratorium on
the work. It would appear that the idea of cloning humans remains unpalatable
for society as a whole, for the time being. I am intrigued by societies
rather strong "gut reaction". Professor Len Doyal (St Bart`s) often talks
of the slipper slope or his "Granny" test as to how society makes ethical
decisions. Probably human cloning currently fails on both these counts.
Yet, on a personal level, I am aware that a number of scientists and clinicians
do not necessarily share these concerns, but publicly "toe the line". It
is hard to know why? Perhaps it has something to do with allaying public
fears? The technique used by Ian Wilmut and colleagues (nuclear transfer),
popularly called "cloning" is still highly inefficient. It took several
hundred eggs to produce one normal live birth.If we had a similar number
of spare human eggs, immediately available, to play with, one might speculate
that, using the same method, a human clone might be created within a year
or so. However, human eggs are a rather valuable commodity and in the UK
it is hard to see how so many eggs might be obtained since all spare eggs
are currently snapped up for use in egg donation programmes. Human cloning
may not be far off. I do not see a world where cloning will be done to
mass produce platoons of supermen, rather a world where cloning will be
used to advance human medicine. Human cloning will come only when society
is able to cope with the benefits it will bring. This may be tomorrow,
next year or next century...