mtDNA confusion

[Guest spottedlizard]

I'm a bit confused about something. I've read that you can take the nucleus of a cell (at least I believe it is just the nucleus), and inject that into the membrane of another cell. I believe the membrane would also contain the cytoplasm, right? For example, cell A and cell B. If I take the nucleus from cell A and insert it into cell B (with it's nucleus removed), that cell would contain the cytoplasm of cell B, right? Or would it be the cytoplasm from cell A??

The reason I ask is because, if I recall correctly, we learned in class that the mitochondrial DNA is present in the cytoplasm. The mtDNA from a mother snail will determine the direction of shell coiling in the offspring. I was wondering what sort of effect this could have upon genetic engineering. Like, say, if I put that snail nucleus into a rabbit membrane with rabbit cytoplasm. How would the snail shell coil? ...the maternal mtDNA is that of a rabbit! Or if I put a frog nucleus in a snail membrane with snail cytoplasm, would this affect the developing frog at all??

[blike]

Most nuclear transfer techniques involve a process called electroporation in which the nDNA and mtDNA is transferred into the recipient enucleated oocyte. Thus, the hybrid cell will contain cytoplasm from both cells. I'm reading the abstract of a paper here written about the cloned sheep Dolly, and 9 other clones. They noted that although theoretically the mtDNA should be trasnferred into the oocyte, all of the ten cloned sheep derived their mtDNA soley from the oocyte, and not from the donor cell. Thus, they derived their nuclear DNA through nuclear transfer, and are authentic nuclear clones, but their mtDNA came from the oocyte, and hence they are "chimeras".

 

http://www.nature.com/cgi-taf/DynaPage.taf?file=/ng/journal/v23/n1/abs/ng0999_90.html

 

Probably won't work because some of the necessary DNA will not be present. I have read about experiments where human mitochondria were tested with other animals nuclei, but neither could function properly.

 

Waksmundzka, M; Journal of Experimental Zoology; 1994; 269(6):551-559

 

That paper (if you have access) discusses rat-mouse nuclear transfers. The scientists injected rat nuclei into mouse ooctyes and implanted the embryos into female mice. The embryos terminated at very early stages, typically between the time the embryo was 5 to 8 cells.

[Guest spottedlizard]

Hmm....

 

That was a really interesting article. I'm going to try to find the other one, I think that's really interesting how mtDNA can have such a huge impact on the development of an organism. Thanks Blike

[fafalone]

When considering genetic engineering its important to note that environmental factors also contribute to development. In an experiment that involved cloning cats, the cloned cats had idential DNA, but the appearance of their fur (color, pattern, etc) was competely different than the original.

[Skye]

I was reading a while ago on these problems with IVF, with some partners who have been unable to get it work, doctors try to transplant mitochondria. I believe the idea is that the oocyte mitochondria and implanted nuclear DNA produce incompatible products, but it's been criticised because no clinical trials have shown it to be effective (I don't know if any have been done though).

 

I didn't think the snail shell coil was determined by mtDNA (there're very few mtDNA genes), but by maternal nuclear DNA, so I googled and got a few lecture notes that were really ambiguous, explaining maternal and mtDNA then using snail shell coiling as an example (of which???). I got this though, "snail shell coiling-orientation of first mitotic spindle is directed by maternal nuclear genes. This assymetry affects direction of shell coil."

 

From here: http://berglab.gs.washington.edu/members/steve/July.28.More.Extranuclear.html

 

So I think it's due to maternal nuclear DNA....

[Guest spottedlizard]

...Thanks,

hmmm... I think that just about fixes my problem about the mtDNA then. But the maternal nDNA would be found in the oocyte, right? It doesn't come from the transplanted DNA. So that would create a problem as well I think (?). Maybe this is partially to blame for all those clones that don't look like the thing they are cloned from (on top of the environmental factors, and any others there may be).

[Skye]

Normally an unfertilised egg would contain the maternal nuclear DNA, which then unites with the paternal nuclear DNA to get the full complement of chromosomes. When an egg (oocyte that is) is used for cloning, it is enucleated, i.e. the unfertilised maternal nucleus is removed. Then the desired nucleus is implanted.

 

So if everything goes smoothly, the resulting cell should only contain nuclear DNA from the implanted nucleus.