The foutain of youth?

Eric R. Hugo eric at
Tue Apr 14 22:56:02 EST 1992

I'd like to point out some possible wrong assumptions with the previous
post on this subject.

Firstly, at least in reproduction, the complex patterns of methylation
that have been seen in somatic cells (but not fully understood) are not
necessarily maintained in germ cells.  In most (if not all systems)
germ cells are partitioned away from somatic cells very early in the
developmental process, and thus remain totipotent.  There are a few
examples of nuclear transplantation experiments where somatic
nuclei have been transplanted into enucleated/fertilized ova.  To the
best of my knowledge, the most developed organism that this has been
sucessful with has been amphibians and that was using nuclei from
tadpole somatic cells (ie. not fully developed).  There have been some
claims of experiments using mammalian nuclear transplants but as far
as I know these are very controversial.  This should point out that
the fertilization/early embryonic development does NOT 'renew' the
potency of the hereditary material.
     As to error correction during fertilization, I do not believe this
to be a factual statement.  This is not to say that there isn't DNA
repair occurring, just that there is no comparison between parental strands
To the best of my knowledge, there is no
mechanism for comparing DNA strands between parents.  If you think about
this, first how would the replication repair machinery Know which was
the correct strand, and secondly there is no reason to believe that the
genetic material from one parent would be identical to the other.
As far as I know the only time Holliday structures and the like are formed
between HOMOLOGs as opposed to chomatids is during meiotic (prophase I)
division in sex cell development.
     All of the preceding is not to say that someday it MIGHT be possible
to grow a new body or rejuvenate an old one, but given today's level
of expertese I think we have a ways to go.
  Eric R. Hugo, Postdoctoral Research Associate |eric at
  Dept. of Biochemistry and Molecular Biophysics|                
  Washington University School of Medicine      |               
  Box 8231, St. Louis, MO 63110_________________| (314) 362-3342

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