the foutain of youth.

Eric R. Hugo eric at bcserv.wustl.edu
Sat Apr 25 09:42:30 EST 1992


>>> There is the protective mechanism (to the mother) of spontaneous
>>> abortion; through this mechanism, the mother is kept from having to put
>>> energy, etc. into maintaining a defective fetus.
>>
>> If DNA damage actually does play a major role in aging, then
>> the parent's DNA will contain more errors than their offspring.
>> This can only be explained by one of the following mechanisms or
>> possibly of combination of them working together:
>>
>>     1. The DNA contained in germ cells is much more immune to the damage
>>        mechanisms that introduce errors into the DNA of somatic cells.
>        Spontaneous abortions are at a much higher rate than most people
>realize. Generally, they happen before the mother is even aware of the
>pregnancy; she will appear to simply have a heavier, possibly off-timed,
>period.
>        Given that much DNA damage takes place at the time of replication,
>it's unsurprising that egg cells wouldn't have that much damage. They
>don't replicate after some point (I believe either infancy or in the fetal
>state). I'm not sure off-hand how many divisions they are from the initial
>fertilized egg, but I'd suspect them not to be very many away.
>        -Allen

Eggs are arrested in prophase I (I think) of meiosis.  This occurs during
fetal development.  The remainder of meiosis does not occur until near 
ovulation, which means that for a woman near the end of the fertile
part of her lifespan eggs may have been arrested for upwards of 50 years.
There have been quite a few studies on spontaneous abortions that indicate
that gross chromosomal aberrations are apparent in many cases.  Some of
this include aneuploidy (extra or missing chromosomes) and polyploidy.
These results suggest that these miscarriages are due to failures in
the mitotic machinery and not necessarily mutations in the actual DNA.
This incidence of Down's syndrome (trisomy 21) vs maternal age tends
to lend some credence to these observations.
-- 
  Eric R. Hugo, Postdoctoral Research Associate |eric at bcserv.wustl.edu
  Dept. of Biochemistry and Molecular Biophysics|                
  Washington University School of Medicine      |               
  Box 8231, St. Louis, MO 63110_________________| (314) 362-3342




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