for a long long time now it has been said that the millionaire sites that are present at birth are all the oocytes a female will ever have in her life because the dogma was that the mitotic proliferation that gives rise to the oocytes initially is restricted to fetal life and that there's no mitosis of the orgonia the stem cells the gamete precursors once an individual is born but nearly 10 years ago the dogma was challenged because of this paper here in nature medicine which suggested that actually there are some ogonial stem cells still present in the adult ovary so what they did was to take some biopsies of ovary represented by this blue oval here from a healthy young woman of reproductive age and they then try to isolate the cells from the ovary that express the protein ddx4 using a ddx4 specific antibody so why dx4 well ddx4 stands for dead box polypeptide 4 and it's an evolutionary conserved germ cell specific rna helicase so their reasoning was that if they were able to obtain cells using this antibody then those cells must be mitotically active and indeed they were able to isolate cells only small numbers but still they were able to isolate cells using this approach indicating that mitotically active germ cells are indeed present in the adult ovary then what they did was to label the cells with a fluorescent protein green fluorescent protein and then they introduced these label cells which they were saying were mitotically active back into biopsies of human ovaries and then they looked to see what happened to those cells that they had isolated and as you can see here they were able to see numerous gfp positive cells throughout the tissue and many of them form aggregates that look very much like follicles so then they went one step further and took the biopsies that they'd introduced the isolated cells into and put them into mice they put them into skid mice so that they wouldn't introduce an immune reaction and then they looked to see what happened to the isolated cells once they were in the mouse and here you can see the data when they looked in the ovaries of these mice they saw loads of gfp negative oocytes so these are the oocytes that were present in the mouse endogenously you can see here the follicle you can see the unlabeled oocyte in the middle and you can see around the outside the single layer of granulosa cells so these are the follicles that are endogenous to the mouse however they were also able to see numerous follicles that stain positive for gfp and here they've used an antibody to recognize gfp rather than fluorescence and so you're looking for brown staining and you can see from this biopsy that there were numerous follicles that stain for brown and so this means that the oocyte is being tagged with gfp which means it must have come from the human biopsy in the first place and so this suggests that it is possible for oocytes to form from mitotically active germ cells that can be isolated from the adult ovary and if this technology has progressed i'm sure you can appreciate that it might open up new areas for assisted reproduction another new area for assisted reproduction has come from some more recent work about trying to generate humans oocytes from stem cells at the moment this work is just in the mouse and what they did was to take mouse pluripotent stem cells and they have both embryonic and induced pluripotent stem cells and they've differentiated them in vitro into something that resembles the primordial germ cells that we were just looking at and then once they've got them that far they then try to reconstitute the ovary in vitro by mixing these primordial germ cell like cells that they generated with somatic cells that they'd obtained from mouse ovaries they mix them together and then they were able to see the development of the follicles and the follicles could grow and mature and when they got them to a sufficiently mature stage they then introduced these oocytes into the mouse and the oocytes were capable of being fertilized and were capable of giving rise to viable pregnancies which resulted in live births and then they followed up the pups for nearly a year and those pups appeared to be really healthy so in humans at the moment we're able as part of assisted reproduction technologies to take our sites uh but at a much more mature stage than these guys were doing with the mouse and we know that those oocytes can give rise to viable pregnancies and live births but what we can't currently do at the moment is is this pre-stage but if we're able to translate this work that's going on in the mouse into the human then you can see that this would bypass a lot of the issues that occur in relation to assisted reproduction and so getting sufficient oversights both in terms of number but also oversights that are of appropriate quality so this might be helpful in the future but as i'm sure you can appreciate there's going to be a whole load of technical challenges and probably a whole load of ethical challenges before we can get to that point but such work could open up new infertility avenues in the future