Dr. Anne McLaren of the Welcome Trust Cancer Research UK Gurdon Institute of the University of Cambridge. Professor Anne McLaren was arguably the most accomplished developmental biologist in the world at this time.
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I’m sure that many of you have known Dr McLaren for your entire for your entire training career. I’ve known Dr McLaren for as long as I’ve known what eggs were and have had the good fortune to meet her a couple of times through the years, so we’re just delighted she’s here.
She’s actually here visiting Dr Biggers and Betsy and spent a couple of days in New Hampshire, so we’re thrilled to have her and I’ve asked John to introduce her because Dr Big knows her career and her goals and her future goals. One of the things I think everyone in this room is aware of is that a challenge that faces any kind of stem‑cell researcher—especially if you want to do what the South Koreans just did—is the ethical issues associated with asking women to donate eggs simply for research.
Although we’ve sort of fussed with that for some time, I think we have that pretty well in hand as a foundation. The country at large is still struggling with that, and Great Britain has paved the way for years on establishing ethical standards for this kind of research, and Dr McLaren has been a major player there.
I’m sure that John is going to tell us a little bit about her career. It’s a pleasure for me to introduce her. She’s been a long‑term friend and a former colleague of mine. I think we first started working together in 1956 and she’s had a very distinguished career.
I’m not going to begin to cover all the things, but she is a Fellow of the Royal Society of London and had the distinction of becoming the first woman to hold office in that body. She was Foreign Secretary of the Royal Society for five years, former president of the British Society for the Study of Fertility, and president of Developmental Biology. She played a significant role as a member of the British Warnock Committee, developing the legislation—the White Report—that led to what some regard as model laws regulating experimentation on human embryos. She testified before the British Parliament on this subject, represented Britain on ethics committees in Europe, and was awarded a distinguished Japan Prize two or three years ago. You can see she’s had a remarkable career, and I’d like now to introduce her to give her talk.
Well, thank you, John, for those kind words, and I’m very grateful to Anne for inviting me to talk at this activated‑egg symposium. I was delighted and honored, but also somewhat reluctant because I don’t work on eggs, have never worked on eggs, and don’t actually know much about eggs.
What I thought I’d do is go through all the reasons we might want eggs and then how we can get hold of them. That’s what this talk will be about. I don’t know how long it’ll be because I wasn’t told until about five minutes ago what the program was. Let’s see how it goes.
Human eggs—first of all, why do we need them? Here is a human egg with its first polar body and its second metaphase plate and nice cumulus cells all around it. I think that’s a human egg, and I reckon there are three main reasons we need eggs: traditional, clinical, and research.
The traditional use of eggs doesn’t need much explanation. At the top, one of my favorite paintings, Cranach’s Adam and Eve, and at the bottom, Mars and Venus. That’s all I shall say about the traditional purpose of eggs. It’s obviously to make babies, and none of us would be here if it weren’t for eggs.
Then what about clinical? Unfortunately, there are a number of women and couples who aren’t able to make babies that easily, and assisted reproduction or infertility treatment has become a big thing. One of the major causes of infertility is problems with ovulation, but this is one of the easiest problems to treat by hormone therapy.
The dose of hormone must be carefully controlled, and ultrasound screening is very important so that not too many eggs are shed, because there are awful stories of women becoming pregnant with seven, eight, or ten fetuses.
If ovulation isn’t the only problem, then the next step is IVF or ICSI. Egg recovery follows hormonal stimulation, producing more eggs than would normally be shed because not all fertilize or develop. ICSI—injecting a single sperm into the egg—proved amazingly effective. When first introduced, it surprised biologists, as only the “best” sperm were thought to fertilize, but injecting any single sperm at random worked.
One of my favorite paintings, Cranach’s Adam and Eve, and at the bottom we have the more pastoral Mars and Venus. That’s all I shall say about the traditional purpose of eggs. It’s obviously to make babies, and none of us would be here if it weren’t for those eggs.
Then what about clinical? Unfortunately there are a number of women and couples who aren’t able to make babies that easily, and so assisted reproduction and infertility treatment have become a big thing. I think I’m right in saying that one of the major causes of infertility is problems with ovulation, and I’m not a medical person, but I think I’m also right in saying that this is one of the easiest of the infertility problems to treat by hormone treatment.
Of course, the dose of hormone needs to be carefully controlled, and ultrasound screening is very important so there aren’t too many eggs shed, because there are these awful stories of unfortunate women who found themselves pregnant with seven, eight, or ten fetuses.
But then if the ovulation problem is not everything, then obviously it’s IVF or ICSI that comes next. Egg recovery after hormone stimulation yields more eggs than would normally be shed because not all fertilize, and not all the fertilized ones develop.
ICSI, of course, is used if the sperm doesn’t do its stuff with ordinary in vitro fertilization. A single sperm can be injected into the egg, and amazingly, that seems to be very effective. When it was first introduced, people—particularly the sperm biologists—were astonished, because there had been an idea that only the best sperm should reach and fertilize an egg. So taking one at random and injecting it seemed very curious indeed, but it worked remarkably well.
Egg donation is another important reason for wanting eggs. The developmental competence of eggs depends on their age, and age here means the age of the egg, not the age of the woman’s body, because oocytes are formed before birth.
The older the woman, the older the eggs, and as the woman gets older, her eggs become less developmentally competent. Egg donation from younger women can restore a high level of fertility to older women. There are also women who don’t ovulate eggs at all, one cause being Turner’s syndrome, having only one X chromosome instead of two.
These women can carry a pregnancy with the use of a donor egg, and that’s why many people are on waiting lists for donor eggs.
In the United Kingdom, the law is very strict about egg donation—it prohibits payment for eggs but does allow expenses to be reimbursed. There’s also something called egg-sharing, where a woman undergoing IVF donates some of her eggs to another couple in exchange for reduced treatment costs.
That’s the summary of the main clinical uses of eggs—treating infertility and enabling preimplantation genetic diagnosis to avoid passing on genetic disease.
Then the final reason for wanting eggs is for women who need pre‑implantation genetic diagnosis.
There are some couples who are at risk for a serious genetic disease because they are both heterozygous for a gene responsible for one of the many known severe disorders. Previously these couples either had to remain childless, or become pregnant not knowing whether the baby would be born with the genetic defect, and then perhaps undergo chorionic villus sampling or amniocentesis.
If the result was bad, they would usually have a termination of pregnancy. Now pre‑implantation genetic diagnosis, as you know, avoids that. If you start with an eight‑cell embryo, you can take out one or two blastomeres and test those blastomeres—usually by PCR, polymerase chain reaction—to see whether they carry the genetic defect in homozygous form.
Here, there are five embryos that have been sampled, and two of them did indeed carry the defect in homozygous form, so they obviously would not be returned to the woman’s uterus, but the remaining three were normal.
Also the possibility of taking a few cells from the trophectoderm at the blastocyst stage, but although this is explored from a research point of view, it’s not used in clinical practice. This other slide shows that you could also do it after cryopreservation.
So that’s pre‑implantation genetic diagnosis.
Okay, so much for the clinical need for eggs. What about research? Well, I’ve listed a number of types of research here.
First of all, we know a lot about the biochemistry and physiology of eggs, but still not enough. There are many unanswered questions, and if we knew the answers to all those questions it would be easier to design even better culture media for embryos than already exist. As most of you know, John Biggers has been extremely active and influential in this whole area, so if there are any questions about the biochemistry and physiology of eggs and the need for further research in that area, John’s the person to ask.
Then, research about infertility treatment—in vitro maturation. There are clinical conditions, and polycystic ovary syndrome (PCOS) is one of them, where too many follicles start developing and then they get ovulated prematurely at stage seven or stage eight. At that stage they’re not developmentally competent—they would normally mature in the ovary in vivo before ovulation.
If they are ovulated prematurely, they can still be matured in vitro. But again, the conditions, the culture medium, and the hormonal support have not been very well worked out. There have been a number of pregnancies from in‑vitro‑matured eggs that have then been fertilized or injected, but it’s by no means optimal. Recently, treatment with in‑vitro‑matured oocytes has been licensed in the U.K., and there have been some pregnancies, but as I say, this is an area where further research would be extremely useful.
Rejuvenation of aged eggs. This is another question people have tried to address. When I say aged eggs, I mean eggs from older women, which were laid down before birth and which are not as developmentally competent as they should be. It has been suggested that injecting a small amount of cytoplasm from younger eggs would rejuvenate them.
There have been publications on this. There have been women who have had normal babies after such treatment, women who had been trying for years without success. On the other hand, whether or not the pregnancies were really due to the treatment is not established. Because of possible risks, this treatment is not encouraged in the U.S.A., and it is not licensed in the U.K. But again, it’s perhaps something that needs further research.
There are two other clinical or medical problems that fall into the research area at present. One is mitochondrial defects and the other is stem‑cell therapy. I’d like to say a bit about both of those now.
Mitochondria. I’ve always found mitochondria fascinating. They’re those little organelles in the cytoplasm of an egg. I think you have something like one hundred thousand of them, and each mitochondrial DNA strand is circular. There are one hundred thousand little circles, each with only sixteen kilobases of DNA and only thirty‑seven genes. Of those genes, most are RNA‑related, and only thirteen code for proteins.
The proteins they code for are almost all enzymes involved in oxidative phosphorylation—I can never say that word properly—and of course the mitochondria are responsible for providing energy for the cell.
They’re aliens, really—invaders. It appears that back in the distant past, in the primeval soup, little bacteria hitched a ride on larger cells and provided them with more energy, while the larger cell provided nutrition and protection. For instance, the genetic code of mitochondrial DNA is not the same as that of nuclear DNA. They really are outsiders that have become insiders.
The important thing about mitochondria is that they are all inherited from your mother—entirely maternal inheritance. Although the sperm has perhaps half a dozen or so little mitochondria compared with the hundred thousand in the egg, the sperm mitochondria all disappear and get degraded within a few hours of fertilization in normal cases.
Unfortunately, mitochondria sometimes have mutations, just like all DNA does, and they can become defective. At the top here we have a cell with normal, fully energy‑competent mitochondria, but sometimes a mutation develops, and the mitochondria replicate independently and distribute themselves randomly in daughter cells.
You can get quite a variety of cell types: some fully energy‑competent, others hopeless, and every degree in between. These cause respiratory defects that are responsible for a number of very serious diseases, including some that can be lethal, and they are all maternally inherited.
One in ten thousand women have serious mitochondrial genetic defects. That doesn’t necessarily mean they show disease because there may only be a small proportion of defective mitochondria that don’t show up phenotypically. But one in five thousand are at risk of developing the disease.
The diseases are quite varied, and nobody quite understands why. Respiratory failure obviously affects the heart—cardiomyopathy—and also the liver and sensory systems. A lot of deafness and optic problems—retinitis pigmentosa, optic atrophy—have a mitochondrial genetic component. Other affected systems include muscles, the urinary system, thyroid, and diabetes. Occasionally these defects can even lead to death.
So it’s a serious problem, and it’s very difficult to give women who have mild symptoms any sort of sensible genetic counseling.
The reason for that comes from work on mice—this, mind you, is mice, not women—but as often happens, we hope humans behave like mice. In mice, if one has a mitochondrial heteroplasmy, with a mutant mitochondrion around, and you look at primordial germ cells soon after the germ‑cell lineage has been established—which happens during gastrulation—you find that the proportion of mutant mitochondrial DNA is very uniform among different primordial germ cells.
But there are about nine, ten, or eleven cell divisions between the establishment of the germ‑cell lineage and when you get primary oocytes entering meiosis. After that, no further cell division happens until ovulation. During those ten or so divisions, the mitochondrial mutations get segregated independently.
As a result, primary oocytes are highly variable instead of uniform like the primordial germ cells. Some have a lot of mutant mitochondrial DNA, others very few. Since no further cell division occurs up to the time of mature oocytes, you never know whether any particular egg is going to be badly affected.
A baby born after fertilization of such an egg might be very ill, might show no symptoms at all, or might be only mildly affected, like the mother.
This makes genetic counseling very difficult.
Is there a way around this? Well, in principle, there is. If you had a donor egg from a normal woman, you could remove the nuclear genetic material from that egg and transfer into it the two pronuclei from the parent egg, and okay, you might have just a few defective mitochondria transferred along with the nuclei, but mostly you’d have normal, clean, healthy mitochondria there, and the babies would be fine.
Now, this route has not been attempted, as far as I know, in any country. But Professor Doug Turnbull in Newcastle, in the U.K., has been interested for a long time in this possibility because he has many patients who are suffering in this way and want advice. He has just been licensed, after a great deal of argument and discussion, to start a research program on human material.
He’s shown in mice that it works—proof of principle. He’s taken mouse eggs and transferred pronuclei into an empty egg and got babies, and they’re fine—very few of the mutant mitochondria.
What he’s going to do is use eggs from IVF programs that are abnormal in that they have three pronuclei. As you know, these would never be used for clinical treatment in an IVF program. They can be donated for research rather than simply be discarded.
He’s going to remove the pronuclei from both and then put two pronuclei into the other cytoplasm—a reciprocal exchange—so that he has two reconstituted diploid zygotes. He will culture those for two days and do a number of tests. For instance, he’ll remove a blastomere for analysis of the mitochondrial DNA to find out whether it looks normal or not.
If, as often happens, there is some heteroplasmy in the donor eggs, he will be able to tell how much of this type of mitochondria has been transferred to the zygote and vice versa. He’ll continue culturing up to the blastocyst stage to see what proportion of embryos develop that far and whether they look reasonable or not. Then he’ll process those blastocysts for cytogenetic and epigenetic analysis—looking at imprinted genes, methylation patterns, and mitochondrial DNA.
This is a three‑year research program.
He had quite a bit of argument with our licensing authority, the so‑called Human Fertilisation and Embryology Authority (HFEA), because our 1990 Act has a clause stating that changes to “the genetic structure” of a cell or embryo are prohibited.
My argument would be that such a procedure doesn’t change the genetic structure. It changes the genetic content, in the sense of the mitochondrial DNA content. What the 1990 Act was actually concerned about when it referred to genetic structure was transgenesis, because, at that time, transgenic technology was just starting up, and people were very worried that someone might start creating transgenic human embryos.
In this procedure, there’s no change to any gene—it’s simply replacing defective mitochondria with normal mitochondria.
If his research program shows no evidence of abnormalities in those developing human embryos, I think he will then apply for a very limited program of clinical treatment for women who otherwise would not have dared to become pregnant, with careful monitoring and follow‑up.
Okay, then finally, on the research side, stem‑cell therapy, and I’m not going to say much about this because you all know too much about stem‑cell therapy.
You all know that there are all those awful diseases and that there are a whole number of cell types that, if one had a lot of them, could treat those diseases. You know exactly what a stem cell is—that it can make more of itself or it can differentiate into every other cell type you can think of.
You also know that you can get stem cells from an adult—and “adult” always means anything postnatal really—from the brain, bone marrow, or satellite cells of muscle. They’re all very useful for particular purposes and will be even more useful when there’s been more research. Cord blood has stem cells in it—very useful.
Then early embryos—pre‑implantation embryos—can give rise to embryonic stem cells from the blastocyst stage. Unfertilized eggs, if they’re activated parthenogenetically, as Ann Kiang has usefully pointed out, can also be used to make human embryonic stem cells, which would then be immunologically identical with the woman who had provided the unfertilized egg.
Back in the early days of 1998, when Jamie Thompson published the first derivation of human embryonic stem cells, this is what he showed. The upper panel is what he actually did—taking the isolated inner cell mass and culturing it. The bottom panel shows what he hoped might one day happen—that it would make kidney cells, heart cells, bone marrow cells, and so forth, which could be used for therapy. Things are moving on. We’ve probably got this far, but not, I think, really that far though some people would disagree—maybe that will come up later today.
Now, as far as human embryonic stem cells go, and as John Biggers mentioned, one of the major problems is an ethical problem, because of course these come from fertilized eggs. If you believe that the moral value of an embryo from the one‑cell stage onward is equal to that of a newborn baby or an adult human being, as some people do, then any research that causes that embryo to stop developing—even if it was going to die anyway—is akin to murder.
I respect that view, but I don’t agree with it. Most of the people in my country think that the moral value of an embryo increases as it develops, first into a fetus and then into a baby. This point of view was reflected in the U.K. Parliament back in 1990 when that Act was passed. In both our Houses of Parliament there was a strong vote in favor of allowing human embryo research under very strictly regulated and controlled conditions.
They also felt that if a research project required the creation of embryos for research, that also should be allowed, and that has proved to be very useful—though it’s been used in only very few circumstances.
This is a list of the countries that agree with the U.K. in allowing derivation of human embryonic stem cells from spare embryos from IVF. I should, of course, have said that Jamie Thomson got these human embryos from IVF clinics with informed consent of the couple, the woman who was donating the embryos for research.
In most cases, whether they are fresh or have been frozen for some years, if they’re not going to be used for that woman’s treatment nor donated to another woman for treatment, they would simply be allowed to die. It’s these spare embryos that are now often donated for research, and that research can include the derivation of human embryonic stem cells.
However, what’s this got to do with eggs? Nothing much—these are embryos. But if they’re going to be used for therapy, then there’s the problem of graft rejection. If they’ve been derived from an embryo donated by an IVF clinic, they will not be immunologically compatible with the patient who’s being treated with the stem cells.
One possibility being put forward is to use somatic‑cell nuclear transfer—that is, the cloning procedure, the same process of transferring a nucleus from a somatic diploid cell into an empty egg, exactly the procedure used for Dolly the sheep and other cloned animals.
If one used that same procedure on a human egg, the blastocyst and resulting embryonic stem cells would be immunologically compatible with the donor of the somatic nucleus. You all know about this—it’s often called “therapeutic cloning,” which is a dreadful term, because there’s nothing therapeutic about the cloning itself. The stem cells may, perhaps, later be used for therapy, but that’s a separate matter.
Cloning for stem cells would work like this: the patient has the disease; the doctor collects somatic cells, recovers their nuclei, and transfers a nucleus into an empty donor egg whose own genetic material has been removed. The embryo is cultured, the stem cells are recovered and then differentiated into whatever cell type the patient requires for treatment.
Now, I’m very skeptical myself as to whether this labor‑intensive and costly procedure will ever be realistic in any healthcare system. But, as you all know, the recent papers from South Korea have at least provided proof of principle.
As I mentioned, Ann Kiang has suggested that it’s possible to obtain from a woman her own egg, which could develop parthenogenetically, and then you wouldn’t need any donor egg. You could culture those stem cells into whatever tissue type that woman required for treatment—and that would be fine. Tough on you chaps, but there we are; Ann has a point.
This procedure is much more attractive, I think, in the U.K. than in the U.S., because in the U.K. there’s a great shortage of donor eggs. In the U.S., one can at least buy donor eggs. But if a woman could provide her own, the parthenogenetic approach would be far more appealing in the U.K., where obtaining donor eggs is difficult.
Even if one didn’t use the cloning approach, there are other—and perhaps more realistic—ways to get over the graft‑compatibility problem. You can sometimes use stem cells from the patient themselves; you can use genetic manipulation to remove incompatibility antigens; you can create a large stem‑cell bank to provide close genetic matches; you can induce specific immunological tolerance in the patient; and, of course, immunosuppressive drugs continue to improve.
On the other hand, the cloning procedure could still be of enormous importance—not for therapy, in my opinion, but for research. There are patients with very rare genetic diseases, maybe only forty, fifty, or sixty patients in the entire world. We know very little about those genetic disorders. If we could make stem‑cell lines from skin cells of those patients, the research value would be tremendous.
Similarly, for common but genetically complex diseases, such stem‑cell lines would make it easier to identify both genetic and non‑genetic bases of the condition.
As a result of this possibility, two licenses have now been issued in the U.K. for cloning for research—one to Alison Murdoch in Newcastle, who will be looking at diabetes, making stem‑cell lines from diabetic patients, and one to Ian Wilmut in Edinburgh, who’s concerned with motor neuron disease, a very mysterious disorder about which we know almost nothing genetically.
Okay, so that’s the first part—that’s why we need eggs. How can we get them?
Possible sources of oocytes include eggs donated by women, which, for clinical use, is the only practical method at the moment.
Now, the problems here are commercialization—what philosophers call commodification—and the potential exploitation of women. If you pay women large amounts of money, they may donate eggs, but there are health risks. The procedure is time‑consuming and uncomfortable, involving many hormone injections. There are also risks of hyperstimulation unless the ovary is properly monitored by ultrasound, and, of course, hyperstimulation can sometimes lead to death.
There have also been suggestions of a possible link to ovarian cancer, though there’s no solid evidence supporting that.
In Europe—not only in the U.K. but in Europe generally—it isn’t permitted to pay money for egg donation. In the U.S., it is permitted, and I believe quite large sums are sometimes paid. I’ve even heard that some young women can pay their way through college by donating eggs.
So that’s a different ethical stance. In the U.K., we don’t allow payment, but we do allow what’s called egg sharing.
Now, most IVF treatment in the U.K. is private and expensive. Some is covered by the NHS, but not enough, so many couples can’t afford IVF or can only afford one cycle. If the woman produces a reasonable number of eggs that fertilize well, she is permitted to donate some to another couple in need, and in return she gets a second cycle free or at a reduced rate.
The argument in favor of this is that it gives two women a chance at the babies they want; without it, neither would have as good a chance. The argument against is that it amounts to buying eggs. Ethicists debate whether monetary payment is ethically different from exchange in kind, and I’m not going to go into that here.
Failed‑to‑fertilize oocytes—these come from IVF clinics where the egg is placed with sperm 24 hours later—no pronuclei, no fertilization. Now, these eggs have been used—for instance, Roger Pedersen used them in San Francisco—and successfully made human embryonic stem‑cell lines from eggs of this sort. It’s what Alison Murdoch in Newcastle will be using for research, but I don’t think it’s practical, at least for clinical use.
Then in‑vitro maturation of immature or primordial oocytes. Now, we’re not talking about the same sort of in‑vitro maturation that I mentioned earlier—before, we were talking about the stage‑seven or stage‑eight in‑vitro maturation. What I’m talking about now are these little tiny primordial follicles with primary oocytes in them, of which there are, before birth, maybe hundreds of thousands in every ovary, and even after birth tens of thousands. Every adult woman of reproductive age has large numbers of these primordial follicles in the ovary.
If these could be recovered—a small slice of ovary removed and matured in vitro—they could be a source of almost unlimited eggs for donation. John Eppig in Bar Harbor has done a lot of work on this in mice. He managed to mature these to a stage where they could be fertilized, but in the early experiments that he did, out of hundreds and hundreds that he tried, only one turned into a mouse. That mouse was, for obvious reasons, called Eggbert, and it was a miserable mouse—it had all sorts of defects and medical problems. For a while, he abandoned that form of research, but he started again recently. I’m not quite sure what he’s doing differently—I don’t know whether anybody quite knows what he’s doing differently—but anyway, he now has, I believe, dozens of very healthy, fertile, happy Eggberts running around in the lab.
That’s interesting.
Then there’s the possibility—again, for research only—of using animal oocytes. Hui Zhen in China used rabbit oocytes, removing the rabbit genetic material, putting in human skin cells, and getting good blastocysts which were indubitably human in the sense of the nuclear DNA, making stem‑cell lines. But the stem‑cell lines didn’t do all that well, and I haven’t heard much from her recently. There’ve also been attempts, I think, to use cow oocytes in the same way, and this might be useful for research.
Then oocytes derived from embryonic stem cells—this is a fascinating development in my view. A paper, for example, from Hans Schöler’s group, which reports Hübner et al, used embryonic stem cells, which, as we’ve already talked about, are pluripotent and can make all cell types. Because they can make all cell types, it’s reasonable that they should also be able to make germ cells.
Sure enough, when he cultured embryonic stem cells—this is all in mice—he found patches of cells which showed Oct‑4, an oocyte‑specific germ‑cell transgene, lighting up; those are these green patches here. He also found that they sometimes looked as if they were migrating—which is the time at which they show this specific Oct‑4 transgene.
He also found cells that showed this red Vasa protein, which is expressed in post‑migratory germ cells—germ cells after they’ve reached the genital ridge. He got these clumps of cells, rather like those you get in vivo, expressing both the Oct‑4 protein and the Vasa protein. He followed them for another couple of weeks and then found that some of the cells detached and started staining for a marker which is specific for meiosis in germ cells.
These are derived from the ES cells; these are derived in vivo. He showed that the Scp3 marker was expressed in the nucleus, and the nucleus started looking rather diffused in type. The pictures in his paper, of course, are much better than these. Finally, he got cells that looked like mature oocytes—they got extruded from something that looked like a follicle. They had something that looked like a polar body; they were in a zona of sorts but a rather fragile zona.
If these went on for another few weeks—and we’re now up to about six or seven weeks—he found within these groups of somatic (follicle) cells what looked like a two‑cell embryo and eventually three cells. Again, you can see the zona pellucida around sixteen cells sharing the specific Oct‑4 protein, developing into blast‑like objects. Some of the blastocysts looked very like proper blastocysts, and again Oct‑4 in the inner cell mass, and PCR analysis showed that they indeed expressed all the right genetic markers.
These actually look extremely like the sort of pictures one gets from parthenogenetic development of the LT strain of mice. So maybe they have something in common with that. We don’t know whether they’re developmentally competent—these blastocysts were not put back in a uterus, as far as we know.
That’s that, but there are other labs that have also pursued this line. This is a diagram from Asim Sands’ News and Views. For example, in the lab of Geijsen et al, they made embryoid bodies from the ES cells and treated them with retinoic acid, which makes primordial germ cells multiply. They found that some of the somatic cells were expressing the Sry gene, the testis‑specific gene, and within those patches of Sry they got germ cells becoming apparently haploid and turning into what looked very like sperm—which were then injected into eggs to fertilize those eggs.
But again, the blastocysts that resulted from that fertilization, as far as we know, have not got any further in development.
Toyooka et al in Japan—that’s in No’s group—they also got male germ‑cell development from ES cells and put them with testis somatic tissue and got sperm.
In Australia, they’ve done the same sort of thing with human embryonic stem cells and got apparently primordial germ cells and embryoid bodies.
So the final possibility, before I get onto that, oocytes from bone marrow or peripheral blood. This possibility was raised first of all in a paper from Jonathan Tilly’s lab (Johnson et al, last year), where they showed pictures of what they thought were oogenic stem cells in an adult ovary.
The pictures in that paper were not terribly convincing to me—they looked rather like what you get in cultured ovaries when oocytes are actually exiting from the edge of the ovary. I wasn’t convinced they were really undergoing mitosis and dividing, and it wasn’t clear whether any were undergoing meiosis to develop into oocytes.
This year, he has another paper, from the same group, now in Cell, showing that in infertile female mice—whether they were genetically sterile or chemically sterilized—you could apparently get new oocytes appearing if you treated them with a bone‑marrow transplantation or even peripheral‑blood transplantation. He claimed that these adult mouse ovaries could produce hundreds of new oocytes within 24 hours.
That, in itself, is a surprising claim, because normally to get from oogonia to meiotic oocytes takes at least a week, and one couldn’t help wondering whether there were pre‑existing follicles that perhaps, after their chemical treatment, started maturing again.
He used donor‑derived GFP‑labeled oocytes, and they seemed to turn up in the ovaries after the peripheral‑blood transplantation, and the pictures from the bone‑marrow transplants looked particularly convincing—more convincing than the peripheral‑blood transplants.
If this is really true, I think it’s fascinating.
[Applause]