http://www.nytimes.com/2001/12/18/health/genetics/18GLOS.html?pagewanted=print
December 18, 2001
The debate over whether the government
should finance research on embryonic stem cells has forced politicians
and the public to grapple with the arcane language of cell biology. Here
are some terms, as gleaned from reports by the National Institutes of Health
and other sources.
REGENERATIVE MEDICINE
STEM CELLS
EMBRYONIC STEM CELLS
EMBRYONIC GERM CELLS
ADULT STEM CELLS
BLASTOCYST
DIFFERENTIATION
CLONING
THERAPEUTIC CLONING
PARTHENOGENESIS
Copyright 2001 The New York Times
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By THE NEW YORK TIMES
Repairing the body by harnessing
its own repair mechanisms — stem cells and signaling proteins — to renew
damaged tissues and organs.
Master cells that can reproduce
indefinitely to form the specialized cells of tissues and organs.
Derived from the inner cell mass
of a blastocyst, a 4- to 5-day- old embryo, these cells are thought to
be pluripotent — meaning they can grow into any of the body's 260 or so
cell types. Unlike the egg cell which is totipotent, able to form a complete
embryo, the embryonic stem cells do not seem able to form a new blastocyst
and cannot by themselves create a new individual.
Embryonic cells that are set aside
and protected from maturing. They migrate through the fetus to the ovary
or testes, where they form the egg and sperm cells. If removed from the
fetus and grown in culture, they behave much like embryonic stem cells.
Stem cells that dwell in the adult
body and are far less versatile than embryonic stem cells. Each type generates
replacement cells for the particular tissue in which it is found. Scientists
are trying to see if adult stem cells can be reprogrammed to produce cells
beyond their normal range.
A hollow sphere of some 250 cells
that develop four to five days after an egg is fertilized. Inside is a
clump of about 30 cells, the inner cell mass, from which the embryo develops.
When removed and grown in a laboratory dish, cells from the inner cell
mass are called embryonic stem cells. They can be changed while being cultured.
The process in which a stem cell
generates a cell with a specialized function. The process begins when certain
genes are activated and others silenced, causing the bland, shapeless stem
cell to change into some other type of cell.
Creating a genetically identical
organism, through any of several techniques. Dolly the sheep, the first
mammal to be cloned, was created by inserting DNA from the nucleus of a
sheep mammary gland cell into an egg cell emptied of its own nuclear DNA.
The new idea of repairing patients
with their own cells, making a skin cell, say, turn into heart cells to
repair the heart. This would be accomplished by inserting the nucleus of
a patient's skin cell into a donated human egg cell without its own nucleus.
The egg cell would reprogram the skin cell nucleus back into its totipotent
state. After the egg had become a 5-day-old embryo, embryonic stem cells
would be cultured and changed into heart cells for injection into the patient.
Reproduction in which the egg develops
into an embryo without fertilization. Parthenogenesis does not occur in
mammals, but scientists can use chemicals or electricity to stimulate the
eggs of certain animals into dividing as if they had been fertilized. One
company has started experiments with human eggs.