matthew_avison at email.msn.com
Thu Aug 6 06:34:07 EST 1998
Some tissues that constantly proliferate (like skin for example) do so
because the tissues contain stem cells. These cells are constantly dividing
and producing daughters who the differentiate into the main cells of the
tissue (e.g. skin cells). Such tissues usually undergo a constant cell
death at their surface (e.g. skin cells die at the surface and are shed) so
the stem cells are essential to stop the tissue waring away, providing a
constant supply of new cells. The brain as a tissue is very different. It
is not designed to cope with constant waring away of differentiated cells
like the skin is. Therefore there are very few neuronal stem cells to
provide new cells to replace ones that do die. Hence eventually the brain
starts falling apart. For most people, however, they are dead before this
really happens. One of the holy grails of neuroscience is to try and get
neurones to de-differentiate into stem cells, thus allowing a source of
proliferation for people who have got problems with too much neuronal death.
Watch this space.
Interestingly, a reason why neuronal derived tumours are so rare and skin
cancers relatively common is because it is a stem cell going wrong that
usually results in a tumour and so the more stem cells there are, the more
chance of getting a tumour. The most rapidly increasing cancer nowadays
(particularly in men) is Colon cancer, the surface of which is very similar
to skin in terms of its ability to regenerate.
Hope some of this helps.
Matthew B. Avison, University of Bristol, UK.
JJ Miranda wrote in message ...
>FOrgive the ignorance of this question... I'm a chemist...
>I was wondering, does anyone know the cellular or molecular explanation
>as to why brain cells don't grow back when killed? Also, I know thatsome
>brain cells grow back but not others... What distinguishes between these
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