Show your work
Hold up! Meres is actually making a post about science?
Gather round, if you won't be terminally bored by my jargon, and let me tell you a story of how people are, once again, kind of wrong on the internet.
On Wednesday the CBC posted an article about how some scientists in the UK managed to make stem cells undergo meiosis and become very like spermatozoa -- flagella and all. Cool!
The problem I'm seeing is that (quelle surprise) none of the "men on the street" commenting on the article have any bloody clue where this is going, despite the fact that the article correctly notes that this study, aside from being generally edifying, may advance a treatment for male infertility. No, it will not take men out of the reproductive picture, not as things stand. Nor will two women be able to have genetic offspring together, unless they go much, much further with this research. (Of course, the CBC comment section is a black hole of stupid, so rather than tilt at windmills I thought I'd just go on about it here.)
See, the thing is, even if you could make functional-looking sperm-like cells from a female's stem cells -- which based on this research seems entirely feasible -- they wouldn't be any use to an egg. There is a phenomenon called imprinting (not the baby duck kind) that imposes certain modifications on the chromosomes of your gametes -- some genes, for lack of a better term, are turned off, depending on which parent you got them from.
To go back to undergraduate genetics, take the apparent problem of females having two fully functional X chromosomes and males only having one (the Y chromosome does not possess anywhere near the repertoire of genes as X, and different ones besides). You only need one X for functional cells in any case, so women (and XXY males and XXX females) have silenced, compressed extra X chromosomes. The second X is useful in the development of the female reproductive tract, which is the reason X0 females are viable but infertile.
ANYWAY, a small percentage of other genes behave in a similar fashion, if not to the same extent of the almost completely silenced superfluous X. (Also, the X-inactivation occurs primarily in embryogenesis, at random, where imprinting occurs in gametogenesis.)
Before meiosis in the germ line (the cells of your gonads that will generate your eggs or sperm) all epigenetic modifications -- those inherited from the prospective grandparents -- are "cleared". The chromosomes being arranged for division into gametes are reverted into blank slate -- Xs unsilenced, things unmethylated, deacetylated, everything the same. The chromosomes are copied and divided by meiosis into single copies; your germ line cells have 46 chromosomes in pairs, your gametes have 23 singletons. But before these gametes go forth to meet other gametes and make babies, the chromosomes are re-modified. The process is asymmetrical in the sexes. Females and males imprint differently. As the Wiki says: "certain genes are expressed in a parent-of-origin-specific manner." (Speaking vice versa, "repressed".)
It's a very small proportion -- most genes are expressed in pairs, but every so often there is a gene for which only the mother's copy is expressed, or only the father's. In some cases, having both active or inactive causes no difficulty, but in others the effect is striking. A sort of incomplete uniparental disomy occurs, which if you're lucky results in a viable genetic disease, but more often results in embryonic death. And that's with one gene out of whack, not hundreds, as would happen if you put an improperly imprinted artificially-generated sperm cell together with an egg.
So it's complicated, right? It's not as simple as mashing two haploid cells together and finding a surrogate. Due to many factors INCLUDING imprinting, you have to have a paternal cell and a maternal cell, or you're kerfucked (technical term). It's really a wonder sexual reproduction works at ALL, guys.
In order to make viable sperm out of male stem cells, you have to make sure the the meiosis process is complete in all ways -- that imprinting occurs properly. If it's just division without clearing the grandparents' imprinting, you're not going to get a useful sperm. If you can get it to do all that, then voila, you have what looks like a good treatment for male infertility. Simple?
If you wanted to make a sperm cell from a female's stem cell, you have to make sure the imprinting occurs as if that donor was a male. I don't even know if the full mechanism of imprinting is understood to the extent that you could sort that out -- can you cue the stem cell to behave like it is genetically male and imprint the way you want. Neither could you make genetically-viable eggs out of male stem cells.
Genetic problems everywhere!
That's if it's possible to make an "artificial" germ line imprint at all. The nature of the cells, growth conditions, timing, unknown factors may make that insurmountable in today's science. I'm going to have to read this publication to see if they address that. Alas, since this is not anywhere near my field I don't know where they are with this.
Fun with stem cells is good for advancing knowledge in general, but the fertility aspect is a lot more genetically complicated in some ways than the purely autosomal manipulation. The folks in the CBC comments haven't got the faintest clue, of course. They're just worried science will make men unnecessary.
Anyhow, that, my friends, is the REAL reason why Mpreg will not work IRL. I know you were worried about that.
In other news, I'm going to Toronto tomorrow to see Broken Social Scene! For free! With a buddy! Yaye!
... Lunch time.
Gather round, if you won't be terminally bored by my jargon, and let me tell you a story of how people are, once again, kind of wrong on the internet.
On Wednesday the CBC posted an article about how some scientists in the UK managed to make stem cells undergo meiosis and become very like spermatozoa -- flagella and all. Cool!
The problem I'm seeing is that (quelle surprise) none of the "men on the street" commenting on the article have any bloody clue where this is going, despite the fact that the article correctly notes that this study, aside from being generally edifying, may advance a treatment for male infertility. No, it will not take men out of the reproductive picture, not as things stand. Nor will two women be able to have genetic offspring together, unless they go much, much further with this research. (Of course, the CBC comment section is a black hole of stupid, so rather than tilt at windmills I thought I'd just go on about it here.)
See, the thing is, even if you could make functional-looking sperm-like cells from a female's stem cells -- which based on this research seems entirely feasible -- they wouldn't be any use to an egg. There is a phenomenon called imprinting (not the baby duck kind) that imposes certain modifications on the chromosomes of your gametes -- some genes, for lack of a better term, are turned off, depending on which parent you got them from.
To go back to undergraduate genetics, take the apparent problem of females having two fully functional X chromosomes and males only having one (the Y chromosome does not possess anywhere near the repertoire of genes as X, and different ones besides). You only need one X for functional cells in any case, so women (and XXY males and XXX females) have silenced, compressed extra X chromosomes. The second X is useful in the development of the female reproductive tract, which is the reason X0 females are viable but infertile.
ANYWAY, a small percentage of other genes behave in a similar fashion, if not to the same extent of the almost completely silenced superfluous X. (Also, the X-inactivation occurs primarily in embryogenesis, at random, where imprinting occurs in gametogenesis.)
Before meiosis in the germ line (the cells of your gonads that will generate your eggs or sperm) all epigenetic modifications -- those inherited from the prospective grandparents -- are "cleared". The chromosomes being arranged for division into gametes are reverted into blank slate -- Xs unsilenced, things unmethylated, deacetylated, everything the same. The chromosomes are copied and divided by meiosis into single copies; your germ line cells have 46 chromosomes in pairs, your gametes have 23 singletons. But before these gametes go forth to meet other gametes and make babies, the chromosomes are re-modified. The process is asymmetrical in the sexes. Females and males imprint differently. As the Wiki says: "certain genes are expressed in a parent-of-origin-specific manner." (Speaking vice versa, "repressed".)
It's a very small proportion -- most genes are expressed in pairs, but every so often there is a gene for which only the mother's copy is expressed, or only the father's. In some cases, having both active or inactive causes no difficulty, but in others the effect is striking. A sort of incomplete uniparental disomy occurs, which if you're lucky results in a viable genetic disease, but more often results in embryonic death. And that's with one gene out of whack, not hundreds, as would happen if you put an improperly imprinted artificially-generated sperm cell together with an egg.
So it's complicated, right? It's not as simple as mashing two haploid cells together and finding a surrogate. Due to many factors INCLUDING imprinting, you have to have a paternal cell and a maternal cell, or you're kerfucked (technical term). It's really a wonder sexual reproduction works at ALL, guys.
In order to make viable sperm out of male stem cells, you have to make sure the the meiosis process is complete in all ways -- that imprinting occurs properly. If it's just division without clearing the grandparents' imprinting, you're not going to get a useful sperm. If you can get it to do all that, then voila, you have what looks like a good treatment for male infertility. Simple?
If you wanted to make a sperm cell from a female's stem cell, you have to make sure the imprinting occurs as if that donor was a male. I don't even know if the full mechanism of imprinting is understood to the extent that you could sort that out -- can you cue the stem cell to behave like it is genetically male and imprint the way you want. Neither could you make genetically-viable eggs out of male stem cells.
Genetic problems everywhere!
That's if it's possible to make an "artificial" germ line imprint at all. The nature of the cells, growth conditions, timing, unknown factors may make that insurmountable in today's science. I'm going to have to read this publication to see if they address that. Alas, since this is not anywhere near my field I don't know where they are with this.
Fun with stem cells is good for advancing knowledge in general, but the fertility aspect is a lot more genetically complicated in some ways than the purely autosomal manipulation. The folks in the CBC comments haven't got the faintest clue, of course. They're just worried science will make men unnecessary.
Anyhow, that, my friends, is the REAL reason why Mpreg will not work IRL. I know you were worried about that.
In other news, I'm going to Toronto tomorrow to see Broken Social Scene! For free! With a buddy! Yaye!
... Lunch time.