Download PROPERTIES OF STEM CELLS All stem cells share three basic

PROPERTIES OF STEM CELLS
All stem cells share three basic properties,
1. They can divide and renew themselves by mitotic
cell division.
Most somatic cells are limited to about 50 divisions due
to the loss of DNA from the telomeres with each pass
through the cell cycle. It is theorized that the enzyme
telomerase is active in stem cells which allows the lost
telomeres to be replenished.
2. They are unspecialized.
They do not display any specific structures associated
with carrying out specific functions in the body.
3. They can give rise to specialized cell types.
Over 200 different types of specialized cells can be
found in the human body. All arise from stem
cells. The process in which a stem cell becomes
specialized is called differentiation.
Link to the Stem Cell Guy :
http://learn.genetics.utah.edu/content/tech/stemcells/sci
ntro/
THE POTENTIAL OF STEM CELLS
Click here to learn about the potential uses of stem
cells.
THE STEM CELLS PREFERRED FOR
RESEARCH AND THERAPY ARE
PLURIPOTENT

Totipotent stem cells are not typically used in
research or therapy because they are not
abundant. They can only be obtained from a zygote
(offers one cell), and embryos in the 2, 4 and 8 cell
stage (offer 2, 4 or 8 stem cells).
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The multipotent stems cells from an adult or the
umbilical cord are not preferred for research and
therapy because they are so restricted in the type of
cell they can become. The multipotent stem cells of
the umbilical cord are limited to differentiating into
a type of blood cell. Adult stem cells are limited
into differentiating into a cell type specific to a
particular tissue or group of tissues.
Pluripotent stem cells are easier to obtain and still
retain the ability to differentiate into almost every
cell type in the human body.
METHODS FOR CREATING PLURIPOTENT
STEM CELL LINES
1. In Vitro Fertilization
One source of pluripotent stem cells are from embryos
formed in vitro (translates to "in glass") for couples
with fertility problems. During the in vitro fertilization
process, the female is subjected to hormones that will
stimulate multiple secondary oocytes to be released
from the ovary. The secondary oocytes are surgically
removed from her body and fertilized in a test
tube. (Typically between 10 and 30 secondary oocytes
are harvested.) Once the embryos reach the blastocyst
(blastula) stage, a few are selected and implanted into
the female’s uterus. The remaining embryos are
discarded, frozen for future use, or donated for
scientific research. Pluripotent stem cells can be
removed from the donated embryos and used to start a
stem cell line.


Advantages: These stem cells are very abundant (as
many infertility couples do not use all of their
fertilized eggs) and easy to obtain.
Disadvantage: Obtaining these stem cells involves
the destruction of the embryo and this creates
ethical issues. Some feel that the embryos will
ultimately be discarded anyway so they should be
used for research and therapy. Others feel that life
begins at conception and the destruction of the
embryo to obtain its stem cells is unacceptable.
2. Therapeutic Cloning
Pluripotent stem cells can also be created by taking the
nucleus out of an unfertilized egg and injecting the egg
with DNA from a differentiated cell (such as a skin
cell). The "donor" cell nucleus is diploid and already
has the full complement of chromosomes. The egg is
never fertilized by sperm in this process. The "virgin"
egg can be stimulated to divide as a zygote
would. When it reaches the blastocyst (blastula) stage,
pluripotent stem cells can be removed and used to start
a stem cell line. (The stem cells will be genetically
identical to the individual that donated the nucleus.)

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Advantages: Therapeutic cloning allows for the
creation of stem cells that are a genetic match to the
recipient so there are no issues with immune
rejection of the cells. Since the "embryo" not
produced by a sperm fertilizing an egg, fewer
individuals have ethical issues with the procedure.
Disadvantages: Therapeutic cloning has had a very
low success rate. The vast majority of the
"fertilized eggs" don't develop. There are still
ethical issues with this procedure because although
the embryo is created though unconventional
methods, it is still a human embryo and must be
destroyed to harvest the stem cells. There is also
concern that this procedure may lead to the cloning
of humans. If the embryo was allowed to complete
development, it would be a clone of the individual
that donated the skin cell. A final concern is the
question of how the human eggs would be obtained
for the procedure. A large number of unfertilized
eggs would be needed. Could young, healthy
females "sell" their eggs for use in therapeutic
cloning? Is this ethical?
3. Nuclear Reprogramming
This is a new technique for making pluripotent stem
cells that is still under study. Genetically engineered
viruses are used to transfer master regulatory genes into
differentiated skin cells. The addition of these genes
alters the expression of other genes within the cell
reprogramming the cell back to an undifferentiated
state. The "induced pluripotent stem cells" (IPSCs) can
be cultured on petri dishes and should be able to
differentiate into any of the 220 specialized human cell
types.
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Advantages: Nuclear reprogramming would create
genetically matched cells to the individual whose
skin cell had been reprogrammed. It could be used
to repair or replace damaged tissue without concern
that the pluripotent stem cells would be rejected by
the immune system of that individual. In addition,
since the procedure does not involve the creating of
an embryo, there are no ethical issues.

Disadvantages: Creating IPSC's has some
risks. There is no way to control exactly where the
virus inserts its genes into the cell's
chromosomes. The viral genes could insert
themselves into genes that regulate the cell cycle
and cause cancers. In addition, one of the genes
within the genetically engineered virus is a cancer
causing gene. Researchers may find the IPSC's
have subtle yet significant differences from
embryonic stem cells that prevent them from being
able to differentiate in every cell type.
Link to Stem Cell Video
http://www.pbs.org/wgbh/nova/body/stem-cellsresearch.html