Ray..... "On the edge" :-)
EGAD! With the information you conveyed I could start my own lab!
Bottom line: within reasonable limitations a knowledgeable and
properly-funded researcher can culture and harvest additional stem cells
from an original source. Yes?
So, one would not have to create an embryo and then steal its cells for
every experiment or transplant... The imamges of "body factories" seem to
me to be emotional exaggeration.... (I'm now ducking under my desk....:-)
Bill
***************************
-----Original Message-----
From: Ray Strand [mailto:[log in to unmask]]
Sent: Thursday, October 05, 2000 11:59 PM
To: [log in to unmask]
Subject: Re: Stem cells, On-going supply?
"William P. Taggart" wrote:
> One point has eluded me:
>
> Once a researcher has an original supply of stem cells, how often do they
> have to go back for fresh ones? Can't they culture and grow on-going
> supplies right in the lab?
>
> Bill
no and yes
depends on:
cell type
culture techniques
quantities required
passage/age
lab facilities
a lot of techniques are not "standardized"
until recently there has been a limit
to the number of times the cells divide
each time a cell divides--it ages
aging is kept track of by the "telomeres" on the end of each chromosome
the gene for telomerease has been isolated and controlled
leading to incredible possibilities
Dolly, the cloned sheep, has old looking telomeres
but, thats another story.
each time cell growth fills up a culture flask
it becomes "confluent" with the cells touching
and then becoming growth inhibited
(growth inhibition imay not happen with some tumor cell lines however)
before this happens -- it is best to "subculture"
each time a cell line is subcultured,
it is called a "passage" and numbered.
the primary method of subculturing --
is to remove the culture media
rinse with saline and
expose to trypsin (a digestive enzyme) solution.
when the cells float off the bottom of the flask
new media with fetal bovine serum is added back in
(the serum neutralizes the trypsin and contains growth factors)
and then enough is removed to start one or more fresh cultures.
when a cell line is frozen--
the subcultured cells are concentrated by centrifugation
and a solution containing DMSO (antifreeze) is added
transferred to small freezing vials
and cooled at an optimum rate until submerged in liquid nitrogen.
the passage number is recorded for future reference and
is useful for locating the culture closest to the original.
properly frozen cells preserved in liquid nitrogen
can be stored indefinitely, and thawed when needed.
--maintainance is not necessarily cheap
aging cultures are subject to environmental streses--
the most agressive cells may take over--survival of the fittest--
sometimes those are fibroblasts--sometimes other tissues
some may grow better in different culture media or
be hormone dependent or so many other factors
adult stem cells have already "been through the mill",
even before culturing
reverseing differentiation,
or modifying telomeres
or so many things we do not yet understand
must first be undertood--unmodified and pure --in youthful cells.
producing large quantities
for DNA analysis -- or transplantation --
requires modified culturing techniques and materials.
culture techniques require the strictest sterility...
requiring special flasks--many kinds and sizes available,
a special biological hood or cabinet,
that filters any and all bacteria from the air in the cabinet,
pipettes for manipulating the media and measuring
special incubation cabinets that maintain stable and optimum
carbon dioxide levels, temperature, humidity.
law requires strict monitoring of these parameters in clinical labs.
used, disposable items are "contaminated" and a bio-hazardous waste.
many times--with valuable cultures --
backup / redundant systems increase expenses...
what i have described is just the basics
and more than you asked for
"yes or no"
--
..........................................................................
Ray Strand
...on the edge of the prairie abyss ......................
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48/47 dx/40 ?onset
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