Skip to comments.Scientists use 'virgin birth' technique(Cloning Alert!!)
Posted on 04/25/2003 5:37:42 PM PDT by cpforlife.org
By BBC News Online science editor Dr David Whitehouse
In many ways the most interesting announcement from Advanced Cell Technology was not that its scientists had produced a human embryo clone - significant though this was (if confirmed) - but that the researchers had also got a human egg cell to start dividing on its own just like an embryo.
It sounds something like the virgin birth. Technically, it is called parthenogenesis.
The human egg cell develops into an embryo without the addition of any genetic material from a sperm cell. The embryo would be a clone of the mother.
It, too, could be a source of useful stem cells to grow into replacement tissues and organs to treat degenerative diseases.
And for some researchers, it overcomes the ethical dilemmas of "conventional" cloning because a mammal parthenote is incapable - so far as current science thinking is concerned - of become a viable foetus; for others, it will be just another example of science going too far.
Parthenogenesis has been observed in many lower animals, especially insects such as aphids. In many social insects, like the honeybee and the ant, parthenogenesis gives rise to male drones. Fertilised eggs produce female workers and queens.
Some larger animals can reproduce this way - there are a few lizards, for example. Parthenogenesis has also been artificially induced in frogs and snakes, although it quite often results in abnormal development.
Persuading unfertilised eggs to start dividing like embryos was achieved in mice and monkeys fairly recently, but it has never been artificially induced in humans - until now, it would seem.
Normally, it is only when a sperm cell merges with an ovum and a full set of genes is assembled that an embryo is formed and starts to develop.
Mature eggs and sperm usually have only half the genetic material of a typical body cell, to prevent an embryo from having a double set of genes following conception. Eggs halve their genetic complement relatively late in their maturation cycle.
But if an egg cell is somehow activated before that stage, it still has a full set of genes - and could develop into a functioning embryo clone.
Stem cells derived from a parthenogenetically activated embryo would be unlikely to be rejected after transplantation. Such cells might also raise fewer moral dilemmas for some people than would stem cells derived through the "conventional" cloning process.
The ACT scientists suggest that one way this technique could be used would be for a woman with heart disease to have her own egg cells collected and activated in the laboratory to produce stem cells. The stem cells could then be coaxed to become cardiac muscle cells that could be implanted back into the woman to patch a diseased area of the heart.
Using a similar technique to create stem cells to treat a man would be trickier. It would involve some genetic manipulation, such as transferring two nuclei from the man's sperm into an egg that had been stripped of its nucleus. Such "male-only conception", however, is highly speculative and few believe it will ever be possible.
Researchers have reported prompting eggs from mice and rabbits to divide into embryos by exposing them to chemicals. As early as 1983, it was demonstrated that stem cells isolated from parthenogenetic mouse embryos could form a variety of tissues, including nerve and muscle.
In ACT's parthenogenesis experiments, 22 eggs were exposed to chemical activation. After five days of growing in culture dishes, six eggs had developed into what appeared to be embryos, but none clearly contained the so-called inner-cell mass that yields stem cells.
Because for females parthenogenesis would involve cell manipulation with no additional genetic material, it may prove to be a more ethically acceptable method of producing stem cells than the conventional transfer of nuclear DNA material from another person.
Sunday's announcement is a major advance in human genetic manipulation and is more surprising than the production of the first human embryo clones, which commentators had been expecting for some time. It is also an advance with potentially even more far-reaching implications.
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Not quite. It didn't start dividing on its own. It started dividing when it was activated.
From the same article:
In ACT's parthenogenesis experiments, 22 eggs were exposed to chemical activation.
A well-known science writer purposely muddied the waters about this when he wrote an op-ed article for the NYTimes some years back.
An egg and an embryo are NOT the same thing.
I should have guessed ;)
Okay, fair enough - I accept, but I'll need at least a few days to really do a proper search.
Between you and me and the dog named blue, what I'm very worried about are the cross species cloning efforts being done in Japan and South America. It will not be long 'til someone tries a human-swine, or bovine-human. If cordblood stem cells could be coaxed into tissue differentiation yielding useful tissues or organs, I'm not at all opposed to implanting such in a swine or other animal (great ape perhaps) to support it until growth to usable development was evidenced. I am wary of the scientists jumping directly to human models, without the exhaustive other mammalian models being explored first. It has to be motivated by things like greed and lust for acclaim. Hurrying such delicate procedures is disasterous and usually sacrifices lives, human lives. [Experience with the pharmaceutical industry showed me that years ago.] I will have to think more on a reply if and when we find more on the possibilities.
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As you already know, primate reproductive cloning is encountering problems at this time.
The capability of a sex cell with 46 chromosomes (ovum that hasn't matured fully, to reduce its chromosome complement to 23) to be stimulated into dividing is more than just that cell reproducing itself, it is that cell reproducing the individual human from whom the cell was removed!
At the moment when cell division in a conceptus begins, the conceived individual human loses, with each cell division and subsequent division, some capability to build the broadest number of tissue and organ categories. That is an important distinction to note, as the difference between average somatic cells and sex cells. It is the reason why theoretically, two sperm could be fused (each has 23 chromosomes) to form a conceptus and thus an alive embryo. It is also the reason the technician could not use two kidney cells or two liver cells or two glial cells, or even coax one of those cells to begin the differentiation journey that builds the organs and organ systems of an individual human life.
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