Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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A
Adult stem cell
A stem cell that has already started to develop into a particular cell type. These stem cells are found in adult tissue and in other fully developed tissue such as cord blood. Adult stem cells replenish the tissues where they are found, such as new skin that develops when a wound heals. They are able to renew themselves and can sometimes grow into other specialized cells.
B
Blastocyst
A mass of 150 or so cells that develops around 5-14 days after an egg is fertilized. This hollow ball is made up of an outer layer of cells (the trophectoderm), a cavity filled with fluid (the blastocoel), and a cluster of cells on the interior (the inner cell mass). Embryonic stem cells make up the inner cell mass. A blastocyst is smaller than the period at the end of this sentence.
Bone marrow stromal cells
A supporting cell found in bone marrow that provides signals to support survival and/or differentiation of blood-forming stem cells.
C
Cell-based therapies
Treatments using stem cells that have grown into a specific type of cell that is needed to repair or replace damaged tissues.
Cell culture
Cells growing in vitro (“in glass” or in the laboratory) on an artificial medium such as in a test tube. Scientists use these cells for their research.
Cell division
When a single cell divides to create two cells. Repeated division allows a group of cells to increase in number or maintain its numbers.
Cell line
A cell line, also called an embryonic stem cell line, refers to all cells that were created from a single stem cell. Similar to the way that family members can be traced back to one common ancestor, stem cells can be traced back to one original stem cell. These cells are then said to be one “cell line.” Cell lines can include many millions of identical cells and scientists believe these cells can divide and exist forever.
Chimera
An animal or person whose body contains living tissue or cells from two genetically distinct individuals. Chimeras can contain tissue from the same species or two different species, but the combination of tissues is not the result of breeding and there is no genetic mixing (all cells maintain their original DNA).
Chromosomes
These are found inside the nucleus of a cell and are made up of long strands of DNA. They are duplicated every time a cell divides. Chromosomes pass on the genes of the organism from one generation to the next.
Clone
A cell, or line of cells, that is genetically identical to an original cell.
Cloning
When cells are copied so that their genetic material, or DNA, matches exactly. Also see definitions for nuclear transfer, therapeutic cloning and reproductive cloning.
Culture medium
The fluid that surrounds cells in a cell culture. It has nutrients to feed and sustain the cells. Scientists can add other ingredients to help make the cells grow into specialized cells.
D
Differentiation
When a stem cell grows into a specialized cell like a heart, muscle, or bone cell. Only stem cells can grow into these specialized cells.
Directed differentiation
When a scientist changes a cell culture to make stem cells to grow into a particular cell type.
Disease Specific Stem Cells
Stem cell lines, developed through somatic cell nuclear transfer (SCNT), that have a specific disease.
DNA
Deoxyribonucleic acid, or DNA, is the “blueprint” of life. It is a chemical found in the nucleus of cells that contains the genetic instructions for developing the body and its functions.
E
Ectoderm
The outside layer of the cells of the inner cell mass of the blastocyst. If these cells develop fully, they grow into skin, nerve and brain cells.
Embryo
A fertilized egg in the process of development until the eighth week of growth. After the eighth week, it is known as a fetus.
Embryonic stem cells
Blank, unspecialized cells found in a blastocyst. These cells have the ability to grow into any and every cell in the body. They also have the ability to continue to multiply and exist indefinitely. Human embryonic stem cells are also known as “hESC” or “human ES cell”.
Embryonic stem cell line
A “line” refers to all cells that were created from a single stem cell. Similar to the way that family members can be traced back to one common ancestor, stem cells can be traced back to one original stem cell. These cells are then said to be one “cell line.” Cell lines can include many millions of identical cells that are thought to be able to divide and exist indefinitely.
F
Feeder layer
These cells work in the culture medium to feed stem cells. Some feeder layers are made of mouse cells. Any stem cells grown with mouse feeder cells can not be used for therapies in humans. Scientists have begun using other materials, such as human cells from placentas, so that those stem cells would be safe to use in humans.
Fertilization
When a sperm and an egg (oocyte) unite.
G
Gene
This part of DNA holds heredity information. Genes control how cells function, in part by controlling the production of enzymes and other proteins.
H
Hematopoietic stem cell
An adult stem cell found in bone marrow. These stem cells have partially developed into blood cells and can further develop into all types of blood cells, such as white blood cells or platelets.
Human reproductive cloning
See definition for reproductive cloning.
I
In vitro
This phrase means “in glass”. It refers to an artificial environment, such as a test tube or laboratory dish, where cells are stored and grown.
In vitro fertilization
A process used to help a couple fertilize an egg outside the body.
In vivo
This phrase means “in body” and refers to something inside a living body.
Inner cell mass
Cluster of stem cells inside the blastocyst. These cells are completely blank and can grow into all cells in the body.
J
K
L
M
Multipotent
The ability to grow into at least two different types of specialized cells.
Myelin
A covering made of fats and proteins that surrounds nerve cells. It protects nerves and helps them work better.
N
Neural stem cell
An adult stem cell found in nerve tissue. These stem cells have partially developed into nerve cells and can further develop into all types of nerves, such as motor neurons and astrocytes.
Neuron
Cells of the nervous system are called nerve cells or neurons. They carry "messages" to other parts of the body using electricity and chemicals. The human brain has about 100 billion neurons.
Nuclear Transfer
Also known as “somatic cell nuclear transfer (SCNT)”, this is when cells are copied so that their genetic material, or DNA, matches exactly. To carry out the process, scientists remove the nucleus (containing the DNA) from an unfertilized egg and replace it with the nucleus (containing the DNA) from the cell of a patient who has a disease. The egg, with the new genetic material, converts to a blastocyst which contains stem cells that match the patient and has the disease. This offers scientists a unique way to learn about diseases and test new therapies on human cells. By testing therapies on human cells before testing them on living people, scientists can make therapies more safe and effective. This could also reduce risk of clinical trials and the time it takes to get therapies to patients. Scientists hope to use this technique to better understand diseases by developing stem cell lines that have a specific disease. These are known as disease specific or patient specific stem cells. Stem cells derived from SCNT may eventually be useful as therapeutics, as they will not be rejected by the individual from which the nucleus was obtained.
O
Oligodendrocyte
These are nerve cells that make myelin to insulate other nerve cells. This protects them and helps them work better.
Oocyte
An unfertilized egg, which is a single cell.
P
Patient Specific Stem Cells
Stem cell lines, developed through somatic cell nuclear transfer (SCNT), that match a patient. These cells could be useful as therapeutics to replace disease tissues or, in the case of cells from someone with a genetic disease, to study how the disease occurs.
Plasticity
This is how well cells of one type will take on the characteristics of more mature, specialized cells. Stem cells can grow into nearly every cell type and so are said to have a lot of plasticity.
Pluripotent
The ability to grow into many different types of specialized cells.
Progenitor cell
This is a cell that comes from stem cells, but it can no longer multiply and exist indefinitely. This cell can still grow into many kinds of cells in the body, but it can’t renew itself. This type of cell is often confused with a stem cell. A progenitor cell is more limited in the kinds of cells it can become than a stem cell. Progenitor cells have begun developing into a specialized cell and have progressed too far to be considered an adult stem cell.
Proliferation
When a line of cells grows because cells continuously divide. Each single cell can divide into two exact copies. Each of those copies can divide into two more, and so on.
Q
R
Regenerative or reparative medicine
When stem cells are grown into a specialized cell and then transplanted into a patient. Those cells then repair or replace damaged cells. For example, a scientist could make a stem cell grow into a nerve cell that produces dopamine. Those cells could be transplanted to a patient with Parkinson’s disease and the new cells would grow and replace the damaged cells, which are no longer effectively producing dopamine, in the patient’s brain.
Reproductive Cloning
Also known as “human cloning.” When cells are copied with the intention of creating a cloned embryo to put into a uterus and create a pregnancy. Scientists, and Americans for Cures, agree that this type of cloning is unethical. It is illegal in California and other states.
S
Self-renewal
The ability of stem cells to renew themselves by continuously dividing. Each single cell can divide into two exact copies. Each of those copies can divide into two more, and so on. Stem cells’ ability to self-renew appears to be unlimited.
Signals
The messages received by cells that control changes in the cell structure and function.
Somatic Cell Nuclear Transfer (SCNT)
See definition for nuclear transfer.
Stem cells
These are blank, unspecialized cells that have the ability to grow into many different types of cells in the body. They also have the ability to continue to multiply and exist indefinitely. Stem cells can be found in blastocysts (days old embryos) or in other tissue such as cord blood and bone marrow. The main types of stem cells include embryonic stem cells and adult stem cells. Stem cells from cord blood are considered adult since they have partially developed into blood cells.
Surface markers
These are proteins on the outside surface of cells. These markers are unique for certain types of cells. Scientists can use antibodies, dyes, or other methods to interact with the markers to identify cell types.
T
Teratoma
A non-cancerous tumor made of cells from the three embryonic germ layers. Teratomas can be created in animals by injecting them with stem cells that have not started to develop into a more specialized cell.
Therapeutic cloning
When cells are copied with the intention of creating matching cells. Also see definition for nuclear transfer.
Totipotency
The ability to grow into every different type of specialized cell.
Transdifferentiation
When adult stem cells from one type of tissue grow into cells of another type. An example of this would be stem cells from bone marrow, which are already partially developed to be blood cells, growing into heart cells when they are injected into the heart.
Trophoblast
This is the outer layer of the blastocyst. If the blastocyst were to be put into a uterus, this outside layer would help the embryo attach to the uterus and, if successful, would become the placenta.
U
Umbilical cord stem cells
Adult stem cells found in the umbilical cord during and shortly after delivery. These stem cells have partially developed into blood cells and can further develop into all types of blood cells, such as white blood cells or platelets. Cord blood stem cells are similar to bone marrow stem cells and are used to treat leukemia and other blood diseases. Similar to blood banks, there are cord blood banks that store cord blood donated for research.
Undifferentiated
When a stem cell hasn’t grown into a specialized cell like a heart or bone cell. When stem cells are undifferentiated they still have the ability to grow into a specialized cell.
V
W
X
Y
Z
Zygote
When a sperm and an egg (oocyte) unite, they create a zygote. After that, cells begin to divide to create the blastocyst.
