Re: mitochondrial DNA and Sperm RNA

["Tim Gwinn" <***>]

Hi Judith,

Good points. Here's an instructive page on mitochondria from the U. of Texas
Medical Branch, Cell Biology Graduate Program. (The page was updated this
month, but the text is copyright 1998, so I am guessing the information is
still current.) Under the Lifecycle page link it says:
"In mammals, 99.99% of mitochondrial DNA (mtDNA) is inherited from the
mother.  This is because the sperm carries its mitochondria around a portion
of its tail and has only about 100 mitochondria compared to 100,000 in the
oocyte. As the cells develop, more and more of the mtDNA from males is
diluted out.  Hence less than one part in 10^4 or 0.01% of the mtDNA is
paternal."
http://cellbio.utmb.edu/cellbio/mitoch1.htm#Menu

If true, this - along with the fact that mitochondria engage in their own
independent replication - would probably also explain why the mitochondrial
DNA in a given cell are all identical (or 99.99% identical, I suppose).

I agree with you about the limitations of studies, especially a single study
of such a small sample size as the one I listed. I have to believe there are
other, more complete, studies along these lines that have been performed,
but I couldn't find readily them. Perhaps, though, cloning reasearch dollars
and efforts are mostly aimed at going for headline results rather than doing
studies on the "side-issue" of mitochondrial/nuclear DNA mismatches in
cloning.

Regards,
Tim


> -----Original Message-----
> From: ROSEN Forum [mailto:*** Behalf Of Judith
> Rosen
> Sent: Tuesday, December 16, 2003 5:57 PM
> To: ***
> Subject: Re: mitochondrial DNA and Sperm RNA
>
>
> That was a fascinating article, Tim. It was one I hadn't seen before. I
> followed the trail from that one to a whole bunch of others and it seems
> that sperm also carry several thousand "strands of paternal RNA" as well.
> What I want to know is, where the hell do they put it?! Sperm
> travel light!
>
> Another aspect to mitochondrial DNA that isn't often mentioned is that not
> all the mitochondria in a single cell necessarily have identical
> DNA. I find
> that amazing. I don't know under what circumstances this occurs or whether
> it's "the norm" or an anomaly, but if you find any further information on
> that, I'd be very interested.
>
> One other comment worth passing along about results from various studies
> that is often forgotten (but my father used to point it out all the time):
> There are certain questions that need to be kept in mind when
> reading about
> any given scientific study. In this case, those questions include: What
> species of animal were the cells taken from? How does that species differ
> from human beings? Under what conditions were the experiments
> conducted? In
> other words, what context was this study conducted in? Because
> that can make
> all the difference (ie: pregnancies weren't carried to term "in this
> study"... what if the construction project next door to the laboratory was
> upsetting the animals or something else unrelated to the conditions under
> scrutiny that are not reflected in the documented material...)
>
> That's not to say that this study was not useful, maybe it was truly
> reflecting the nature of the thing being studied, but it's always good to
> bear in mind that results of any single study need to be taken with some
> room for doubt.
>
> Judith
>
> ----- Original Message -----
> From: "Tim Gwinn" <***>
> To: <***>
> Sent: Monday, December 15, 2003 11:34 PM
> Subject: Re: [ROSEN] mitochondrial DNA
>
>
> > Hi Judith,
> >
> > In my search tonite, I only found one paper online where they
> compared the
> > efficacy of using maternal donor cells versus "foreign" donor
> cells (which
> > would presumably have different mitochondrial DNA than from a maternal
> cell)
> > in cloning of cows. The paper notes that: "Consequences of constructing
> > clones in a "foreign" egg cytoplasm remain unclear but may contribute to
> the
> > inefficiency of the cloning procedures for producing live, healthy
> > offspring."
> > The conclusion was: "Use of maternal egg cytoplasm for
> constructing cloned
> > embryos did not improve developmental competence of clones to
> establish or
> > maintain a pregnancy to term."
> > I cannot tell what year the paper was written (at least 1998+). It is a
> > short paper, from the Univ. of Tennessee, located at:
> >
> http://animalscience.ag.utk.edu/pdf/Reports/Edwards_LE%20departmen
> tal%20repo
> > rt%20maternal%20cytoplasm%202002.pdf
> >
> >
> > I also found the following item which states that sperm do have
> mitochondria
> > (they apparently do need them to produce energy) but these sperm
> > mitochondria may be chemically tagged for destruction once
> inside an egg:
> > http://www.findarticles.com/cf_dls/m1200/1_157/59021040/p1/article.jhtml
> >
> >
> > It would seem to make sense that mismatches of nuclear and mitochondrial
> DNA
> > ought to promote problems, diseases and death among such clones. But, if
> > this does not bear out, then perhaps the two are not that
> tightly coupled.
> > That might offer some evidence that is suggestive of the notion that the
> > mitochondrial components of cells were seperate organisms(?) at
> one point
> in
> > time, and at some later evolutionary time became endosymbiotes,
> and retain
> > some degree of independence of internal structures from its symbiotic
> > partner. As a symbiote, perhaps as long as the mitochondria serve their
> > functional role for the whole cell, variations in their
> internal structure
> > can be tolerated.
> >
> > Regards,
> > Tim
> >
> >
> > > -----Original Message-----
> > > From: ROSEN Forum [mailto:*** Behalf
> Of Judith
> > > Rosen
> > > Sent: Monday, December 15, 2003 9:34 PM
> > > To: ***
> > > Subject: Re: mitochondrial DNA
> > >
> > >
> > > Off and on over the years, I've done a bit of research into
> mitochondrial
> > > DNA, because I was fascinated with the notion that not all of our
> "genetic
> > > blueprint" is contained in the nuclear DNA. I also found it
> > > interesting that
> > > all mitochondrial DNA is inherited through the mother (because
> > > the egg cell
> > > is large enough to contain mitochondria but the sperm cell is
> not). This
> > > doesn't get talked about very much, and I don't understand
> why that is.
> It
> > > seems to me that if certain inherited human metabolic
> diseases are being
> > > studied, for example, then they ought to be looking into mitochondrial
> > > DNA... but it has never gotten a single mention in any of the studies
> I've
> > > seen.
> > >
> > > With regards to Jeff's experiment idea, I think the mitochondria
> > > must play a
> > > large role in the genetic make up of any offspring resulting
> from an egg
> > > where the mitochondria are not from the same mother as the
> nucleus. Does
> > > anyone know of studies where this aspect of cloning is discussed? It
> seems
> > > to me that the premature aging that we've seen in cloned animals
> > > may be due
> > > to a mismatch in genetic proteins within cells or some other
> side-effect
> > > from this situation.
> > >
> > > Judith
> > >
> > > ----- Original Message -----
> > > From: "Jeff Pridaux" <***>
> > > To: <***>
> > > Sent: Monday, December 15, 2003 1:37 PM
> > > Subject: Re: [ROSEN] SciAm Dec. 2003 - DNA, Epigenetics, and
> Complexity
> > >
> > >
> > > > The following experiment might be interesting:
> > > >
> > > > As I understand it, for animals cloned so far, the DNA from a viable
> egg
> > > > cell is replaced with DNA from another cell (from the same
> > > animal) in such
> > > > a way to "trick" the egg to think it was fertilized.  It may be that
> the
> > > > whole nucleus is swapped out of the egg.  Then the animal (or a like
> > > > animal) carries the fertilized egg to term resulting in a
> clone of the
> > > > animal (who donated the DNA)
> > > >
> > > > An interesting alternative would be to have the donor egg and the
> > > replacing
> > > > DNA being from different animals.  And somehow just swap out the DNA
> > > > without swapping out the surrounding chemicals around the DNA in the
> > > > nucleus.  If that were possible and if an animal resulted
> that wasn't
> > > > exactly the same as the DNA donor, then that would demonstrate that
> the
> > > DNA
> > > > isn't EVERYTHING.
> > > >
> > > > I suspect, though, that this experiment may be very difficult (or
> maybe
> > > > impossible) to perform.
> > > >
> > > >
> > > >
> >
> >
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