Cells and Aging

Robert Ames gnome at istar.ca
Tue Mar 9 16:29:29 EST 1999

In article <36E41D8F.1478738 at ryley.com>, James <james at ryley.com> wrote:
>Robert Ames wrote:

>> It's difficult for me to accept that an infant has all the muscle
>> cells of a grown adult.  Does the uterus of a baby girl, for
>> example, contain the same number of muscle cells as her mother's
>> uterus which surrounded her?

>Why is it difficult for you to accept?  If it's true of skeletal
>muscle (which is generally is), why would smooth muscle be any
>different?  I'm not saying it's not -- I haven't researched it. 
>But there is no reason to speculate otherwise without evidence
>when we know that to be the case with skeletal muscle.

Common sense, James.  The organ in a female infant that will be the
uterus is smaller than your smallest finger, while the mother's
womb was able to encompass the entire body of the baby.

But returning to skeletal muscle cells, I don't think the situation
is so clear-cut as you make it.  A friend has referred me to a
paper by Ferrari et al. in Science 279(5356):1528-30 that contains
this intriguing quote:

  Growth and repair of skeletal muscle are normally mediated by the
  satellite cells that surround muscle fibers. In regenerating
  muscle, however, the number of myogenic precursors exceeds that of
  resident satellite cells, implying migration or recruitment of
  undifferentiated progenitors from other sources.

This being the case, and since telomeres shorten at different rates
depending upon the tissue (e.g. hematopoetic cells are subject to
telomerase), knowing the reproductive state of satellite cells alone
is not sufficient for an inference concerning the turnover (or not)
of skeletal muscle cells.

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