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Biology
Stem cell research
Stem-cell research:
Stem-cell research studies how stem cells
can be extracted and used to treat a variety
of medical conditions and diseases. There
are two basic types of stem cells: adult
stem cells and early, or embryonic, stem
cells. Adult stem cells are partially specialized
cells that can turn into some body cells
and tissues. For example, blood-forming
adult stem cells in bone marrow can turn
into certain types of blood-related cells.
Human adult stem cells are used to treat
about 10 medical conditions, primarily blood-related
diseases, such as certain types of leukemia.
Adult-type stem cells are found in body
tissues, such as tissues in the bodies of
adults and discarded umbilical cords and
placentas. Scientists believe they can be
useful but potentially not as versatile
as early stem cells.
Early stem cells are "pluripotent,"
meaning they are unspecialized cells that
have potential to turn into and regenerate
any type of cell or tissue in the human
body. Scientists believe early stem cells
could provide cures for many currently incurable
or common diseases and injuries, such as
diabetes, Parkinson's, Alzheimer's, sickle
cell disease, cancer, heart disease and
spinal cord injury. There are currently
two sources of early stem cells: leftover
fertility clinic embryos that would otherwise
be discarded and destroyed, and a laboratory
process called Somatic Cell Nuclear Transfer,
which provides a way to make early stem
cells in a lab dish for medical purposes.
Use of these cells from embryos is controversial
for many in the religious community on the
basis that it could amount to human cloning,
an unnatural act of "creation"
taken from the hand of God, with an array
of ethical ramifications; and that embryos
could be -- or develop into -- human beings
with rights to life.
Techniques: Embryos
used in stem-cell research are at the stage
before they would be implanted in a uterus,
usually within one to five days after fertilization.
Stem cells are isolated from the embryo,
which eliminates its potential to develop
into a complete human being. In Somatic
Cell Nuclear Transfer, the nucleus of an
unfertilized egg is removed and replaced
with the nucleus of a patient's body cell
that contains a full set of genetic information.
The patient's genetic material incorporates
into the egg and causes it to develop into
a blastocyst (an early-stage embryo with
about 100 undifferentiated cells) which
almost identically matches the patient's
DNA. This pre-embryo contains a cluster
of stem cells. The inner cell mass of the
embryo is extracted, leaving the stem cells,
and destroying the embryo. This technique
is currently the basis for cloning animals,
such as Dolly the sheep. SCNT research in
humans requires human eggs. The most common
source is eggs extracted from women during
in vitro fertilization procedures in excess
of clinical need. Presently, no human stem
cell lines have been derived from SCNT research.
Some researchers are trying
to find alternative methods of obtaining
embryonic stem cells that don't involve
the death of an embryo. One uses a process
similar to "Pre-implantation Genetic
Diagnosis," a procedure requested by
prospective human parents who are aware
that they are carriers of an incurable genetically-based
disease or disorder and are concerned about
passing the problem to their child. Fertility
clinics extract a single cell from each
embryo produced by the couple and test it
for the genetic problem. Embryos found to
be free of the disorder are implanted in
the woman's womb; defective embryos are
discarded. Scientists used a similar procedure
on two-day-old mouse embryos that contained
eight cells each. They found that a single
cell - called a blastomere - removed from
each embryo behaved like embryonic stem
cells, while the seven remaining cells continued
to develop. Previous research showed that
one or even two cells could be removed from
an eight-cell embryo without adverse effect.
The embryos were implanted in the wombs
of mice, and continued to mature into normal
baby mice. Researchers ended up with only
a single stem cell from each embryo -- rather
than about 150 stem cells harvested from
an entire embryo -- but methods exist to
produce stem cells from a single cell.
In other research on mouse
embryos, researchers used a modified version
of Somatic Cell Nuclear Transfer. They blocked
the action of a key gene in the nucleus
before inserting the nucleus into the egg,
so that the resulting "non-embryonic
entity" would not be able to develop
into a conventional embryo that could be
implanted in a uterus and induce a pregnancy.
Scientists argue that if this technique
were successful with human embryos, "patient-specific"
embryonic stem cells could be produced without
destroying potential human life.
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