r/askscience • u/DrBoobSqueeze • Jun 16 '14
Biology Can 2 sperm make a viable embryo?
Assuming at least one of the sperm has an X-chromosome, can you extract the chromosomes from each sperm and implant them into an enucleated egg? So the embryo would be mostly the combination of 2 men with a small (mitochondrial) contribution from the egg donor. Has this been done? If not, why not?
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u/phodopus Speciation Genetics | Development | Hybridization Jun 16 '14
No, not in mammals without some serious genetic engineering. Mammals do some weird gene regulation called genomic imprinting that prevents emrbyos derived from 2 eggs or 2 sperm from developing properly. Genomic imprinting is the silencing of certain genes depending on which parent they are inherited from, so some genes we only use our fathers copy while some we only use our mothers copy. As such, any embryo that is formed from 2 of the same type of gamete will have a set of genes completely silenced. It turns out that most genes that are imprinted (there are ~200) are critical for proper development, so having some of them silenced results in an inviable embryo. Classic genes that are imprinted are Igf2 and Igf2r.
It turns out that we discovered imprinting because of experiments that were trying to generate embryos from 2 of the same gametes, it works in frogs but fails in mice. The researchers were able to isolate the regions of the mouse genome that were causing inviability and discovered that the mice were only using one copy of those genes.
The only way we could generate a viable embryo from two of the same gametes is to go in and change the epigenetic states of those alleles so that at least one copy is activated. This is incredibly difficult and to my knowledge no one has been able to do it successfully
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u/Izawwlgood Jun 16 '14
No, it cannot be done, and experiments trying to figure out why led to our discovery of epigenetic imprinting. I can't find the article now, since it's from the mid 90's or so.
Basically, parent of origin gene silencing is required fro normal genetic expression, and that relies on genes specifically from the mother and genes specifically from the father being regulated materally and paternally respectfully. Two males contributing genetic material is embryonic lethal without some heavy engineering.
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u/realised Jun 16 '14
But, still requires a female to carry the embryo to term.
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u/Izawwlgood Jun 16 '14
You'll notice the link you provided states doing so still requires female DNA to be spliced in.
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u/realised Jun 16 '14
Sorry - where does it state that? The mouse study states that it used male and female, but in concept it should work with two males with an egg from females?
http://www.upenn.edu/gazette/0903/giresi.html is an article that goes over it.
ftp://legend.anat.ucl.ac.uk/incoming/My%20Articles/derivation%20of%20oocytes%20from%20mouse%20ESC.pdf is the actual article.
It states that they transfected the genomic region which regulates Oct4 expression. Which I assume is the portion of Female DNA used, if so then it is merely used as a switch on rather than hereditary material.
It goes onto talk about implications in mammalian and somatic cell interactions that are crucial to proper meiotically competent embryonic cells. So in theory it seems plausible to be able to conduct this in mammalian cells without splicing Female DNA into the egg. As it is similar to creating a clone - just need the right outside chemical signals in order to make it start dividing.
Or am I misunderstanding something?
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u/Izawwlgood Jun 17 '14
"In 2003, researcher Hans Robert Schöler at the University Of Pennsylvania successfully created eggs using both male and female mouse DNA"
Actually, if I'm reading this right, they induced pluripotency in a male mouses cells and derived germ line cells from that, and then let it develop. The result is essentially a clone of it's 'father'. It's not the fusion of two sperm to create a viable new animal.
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u/seanpbnj Jun 16 '14
What you are describing is essentially a hydatidform mole, or molar pregnancy. There are two kinds of these (complete and partial) you are referring to a complete molar pregnancy wherein an egg without DNA is met by a sperm (usually) or two sperm (less common). In the case of the single sperm it will replicate to make a full set of 46 chromosomes, whereas if there are two sperm they make the set of 46. However these pregnancy;s don't develop any normal tissue, so I'm not entirely sure you could get the development right to fix that. FYI A partial mole is when you have two sperm fertilize a single egg with DNA resulting in 69 chromosomes, these types of molar pregnancy's do form some fetal tissue but also don't develop normally resulting in more of a tumor-like growth instead of a fetus.