This week in “News of the Weird” the lead story is about a researcher (Dr. Paul De Sousa) in Scotland who reported to a meeting of scientists that his group was able to get an unfertilized egg to divide and develop into a blastocyst by using electrical shocks. The goal was to generate stem cells.
I have been unable to find any other reference to this particular story.
If the story is true, I wonder if the resulting embryo has to be an X0. If that’s the case, the embryo would not be a clone of the mother so can the stem cells be used medically without difficulty?
The ethical issue for those who would not want to use such stem cells would not be that the embryo was a clone, but that the embryo was human. And it could easily be argued that the resulting embryo, even if haploid, was still human.
What exactly is the question then? What do you mean by “used medically without difficulty?” Are you asking if haploid stem cells would be able to used for the same medical purposes as diploid cells?
If the cells are reproducing, presumably the 23 chromosomes originally present in the egg cell have been duplicated, so the daughter cells have the normal compliment of 46. If that’s the case, they’d be XX, not XO.
Additionally, it would be sort of a clone, but not really. What they’ve done is taken half of the mother’s genome, then duplicated it. Any alleles not present in the original half would be absent.
I was curious about this myself, since I have not heard of functional mammalian (or vertebrate, for that matter) haploids (aside from germ cells, of course). In bees, wasps, and ants all females are haploid. However, this article (warning: pdf) describes a near haploid human cell line, so I suppose it’s possible.
A Google search tends to confirm **Rusalka’s ** statement that de Souza is producing blastocysts from unfertilized eggs, but I haven’t been able to find enough detail to confirm that the blastocysts are actually haploid.
Anyway, back to the question. No, they can’t be used without medical difficulty. They are genetically distinct from the parent line and so will be recognised as foreign by the immune system. The body actually has some impressive barriers in place to prevent contact between the haploid reproductive cells and the immune sysem for precisely this reason. If those barriers are broken a common result is the gonads suffering from autoimmune problems.
Lacking a suitable term I’ll call a “cell with with chromosome pairs that are all identical due to replictaion from a haploid gamete” a double haploid until someone comes up with a better alternative.
The problem with double-haploid or haploid cells is that althought hey don’t contain any new genetic material they can never contain a complete set of the old material. This presents a problem because the surface antigens of cells can be the result of the expression of several genes. With only half the genome, even if dipoid, these cells are likely to lack some of the genes reponsible for these antigens and have to ‘substitute’ variations, Those variations are not going to be recognised by the host immune system
There will probably be fewer medical complication from these lines simply because they are less likely to contain anything any totally novel proteins. However there is still a risk because the absence of some genes may allow the expression of others that are normally dormant in the original diploid form.
The obvious risk I can see is that the immune system can learn, and once it’s learned it tends to seek. That’s a real danger when damaging on areas of the body that are normally concealed from the immune system like the gonads or the eyes. Even simple surgery on these areas can lead to destruction of the organ system, including the organ that wasn’t damaged. That’s because exposure to the bloodstream allows the immune system to learn what those hidden components look like, and thereafter the occasional exposure to leucocytes primed to their presence will trigger an all-out attack.
If an animal were treated with the haploid/ double haploid cells and the body did mount an immune response it could sensistize the system to the same type of diploid condition in the gonads, rendering the subject steirle.
So it’s not by any means free of complications or potential complications. But it would probably require lower doses of immunosuppresant than using totally foreign stem cells.
I would have thought all english speaking sites would be well served by a search at google.com.
From the “Telegraph” article:
“The parthenote retains the full set of DNA from the egg donor and can be used to make her stem cells. If imprinting errors do not interfere, “tissue we could derive from such an egg and embryo would be compatible for transplantation”, he said.”
Ok, I thought that a human ova was a haploid gamete. This is what is confusing me. How could the egg produce a clone?
OK. That article clears things up a but. It appears De Sousa isn’t just using an unfertilised egg, he’s using a primary oocyte to generate a parthenote. Athough it’s hard to tell because it’s a popular press article and just used the word “egg”.
Somewhat simplified, a meiotic division that produces and “egg” is actually two distinct cell divisions. The original diplod cell replicates all chromosomes and ends up being effectively tetrapolid (4n), having a pair of every pair for a total of 4 copies. This is the state of the ‘eggs’ in the human ovary, termed a primary oocyte. They reach this stage well before the child is born and they sit in that state until they are released duing ovulation.
At ovulation the cell then divides producing two cells, each have one duplicated set of each chromosome. So these two cells each have 2 copies of each chromosome, but the copies are identical to each other and not true chromosome pairs. As a result they are technically diploid, but because they only have one version of each chromosome found in the parent they are functionaly haploid. In humans one of these cells fials to develop any more and is ejected as a “polar body”. The other cell is the secondary oocyte, and the state in which the eggs move down the fallopian tubes awaiting fertilisation.
Shortly after fertilisation the secondary oocyte divides yet again, ejecting yet another polar body. The cell is now very berifly a true diploid with only one copy of every chromosome. These rapidly comobine with the chromosomes from the sperm and we have a normal embryo.
If the article is correct in saying that the “parthenote retains the full set of DNA from the egg donor” then it appears that de Sousa has managed to disrupt this process at the primary oocyte stage. This has been done before for other primates, so it’s not exactly ground breaking in itself, althoughthe first time it’s been done for humans.
He has managed to force the primary oocyte to not divide fully. As a result the primary oocyte develops two nuclei within the one cell, each nucleus corresponding to one of the final nuclei of the secondary oocyte. These are then forced to recombine to produce a normal haploid cell.
So it’s tricky, and interesting, but not all that groundbreaking considering it has been done routinely with other primates for years. It’s also a bit misleading since the diploid/tetraploid primaryoocyte this techniuqe uses isn’t really and “egg” in the normal use of the word. It’s a cell that eventually develops into an egg. WHich is whre your conmfusion stems from. The ove themselves are effetcively haploid but de Susa isn’t unsing ova, he is manufacturing psuedo ova from primary oocytes.
The articles make it seem like the eggs have been donated the conventional way. How would these oocytes be extracted? How would you “force” them not to divide, etc? There were 300 of these eggs used, if it wasn’t a routine procedure, wouldn’t there have been some mention made?
I don’t quite know what you mean by conventional. The article says “immature human eggs are taken, with consent, from women who have been sterilised then grown in the laboratory”. That seems to imply that the oocytes may have been extracted directly from ovaries that were removed from the mother. That’s not conventional practice for any medical procedure that I know of.
However AFAIK for other primates the oocytes were extracted the way they usually are for IVF. I’m far from an expert on IVF, but essentially the animal is given massive injection of the hormones that normally cause follicles to develop. Because the doses are so high numerous follicles develop on each ovary, rather than the normal situation where only on develops on one ovary. Then when an ultrasound shows that the follicles are almost ‘ripe’ another hormone injection causes them to rupture prematurely. The ruptured follicles are then quite literally scraped and sucked of the surface of the ovaries using a laparascope. So these could be collected in the conventional way, or at least the conventional way for IVF treatment, but in the case of de Sousa’s work the collection technique seems to be very unconventional.
My understanding (and take that for whatever you think it’s worth) is that it’s a three part process. First you need to prevent the primary oocyte from dividing fully so that it retains the complete genome albeit in two nuclei within the same cell. This is done by bathing the cell in various chemicals that frankly I don’t understand.
Then you need to trick the oocyte into thinking that it has been fertilised by a spermatozoan so that the two nuclei recombine and the cell starts to divide again. This depends on the entry of the sperm disrupting ion levels within the cell when it dissolves the membrane. It can be mimicked chemically by partially dissolving the cell membrane with something as simple as alcohol, or with chemicals that inhibit the proteins that control ion balance. In this case it seems de Sousa has gone for the oldest technique: subjecting the cells to a constant electrical charge, or as the article puts it “with a shock of electricity”.
Then you need to remove all the hormones that kept the cell from dividing until it was fertilised. Normally the sperm itself will contain the necessary chemicals to inactivate those, but in these cases there is no sperm and if they aren’t; removed the cell will simply refuse to divide even though it now has a fully functional nucleus. So you then bathe the cell in various nasty chemicals including protein inhibitors and proteases that actually destroy proteins. This is suspected of being the step that makes the process fail. The treatments are non-specific enough that although they destroy the inhibitors they destroy a lot of the enzymes needed for later development.
I took it that “immature human eggs are taken, with consent, from women who have been sterilised then grown in the laboratory” was making mention of the fact this wasn’t a routine procedure.