A – Z Glossary
A
Adult (Somatic) stem cell
A relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation. Such cells vary in their differentiation capacity, but it is usually limited to cell types in the organ of origin. This is an active area of investigation.
Astrocyte
A type of supporting (glial) cell found in the nervous system.
B
Blastocoel
The fluid-filled cavity inside the blastocyst, an early, preimplantation stage of the developing embryo.
Bone marrow stromal cells
A population of cells found in bone marrow that are different from blood cells.
Bone marrow stromal stem cells (skeletal stem cells)
A multipotent subset of bone marrow stromal cells able to form bone, cartilage, stromal cells that support blood formation, fat, and fibrous tissue.
C
Cell-based therapies
Treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cells or tissues.
Cell culture
Growth of cells in vitro in an artificial medium for research or medical treatment.
Cell division
Method by which a single cell divides to create two cells. There are two main types of cell division depending on what happens to the chromosomes: mitosis and meiosis.
Culture medium
The liquid that covers cells in a culture dish and contains nutrients to nourish and support the cells. Culture medium may also include growth factors added to produce desired changes in the cells.
D
Differentiation
The process whereby an unspecialized embryonic cell acquires the features of a specialized cell such as a heart, liver, or muscle cell. Differentiation is controlled by the interaction of a cell’s genes with the physical and chemical conditions outside the cell, usually through signaling pathways involving proteins embedded in the cell surface.
Directed differentiation
The manipulation of stem cell culture conditions to induce differentiation into a particular cell type.
E
Ectoderm
The outermost germ layer of cells derived from the inner cell mass of the blastocyst; gives rise to the nervous system, sensory organs, skin, and related structures.
Endoderm
The innermost layer of the cells derived from the inner cell mass of the blastocyst; it gives rise to lungs, other respiratory structures, and digestive organs, or generally “the gut.”
Enucleated
Having had its nucleus removed.
Epigenetic
Having to do with the process by which regulatory proteins can turn genes on or off in a way that can be passed on during cell division.
F
Feeder layer
Cells used in co-culture to maintain pluripotent stem cells. For human embryonic stem cell culture, typical feeder layers include mouse embryonic fibroblasts (MEFs) or human embryonic fibroblasts that have been treated to prevent them from dividing.
G
Gastrulation
The process in which cells proliferate and migrate within the embryo to transform the inner cell mass of the blastocyst stage into an embryocontaining all three primary germ layers.
Germ layers
After the blastocyst stage of embryonic development, the inner cell mass of the blastocyst goes through gastrulation, a period when the inner cell mass becomes organized into three distinct cell layers, called germ layers. The three layers are the ectoderm, the mesoderm, and theendoderm.
H
Hematopoietic stem cell
A stem cell that gives rise to all red and white blood cells and platelets.
I
Inner cell mass (ICM)
The cluster of cells inside the blastocyst. These cells give rise to the embryo and ultimately the fetus. The ICM may be used to generateembryonic stem cells.
L
Long-term self-renewal
The ability of stem cells to replicate themselves by dividing into the same non-specialized cell type over long periods (many months to years) depending on the specific type of stem cell.
M
Mesenchymal stem cells
A term that is currently used to define non-blood adult stem cells from a variety of tissues, although it is not clear that mesenchymal stem cells from different tissues are the same.
Mesoderm
Middle layer of a group of cells derived from the inner cell mass of the blastocyst; it gives rise to bone, muscle, connective tissue, kidneys, and related structures.
Microenvironment
The molecules and compounds such as nutrients and growth factors in the fluid surrounding a cell in an organism or in the laboratory, which play an important role in determining the characteristics of the cell.
Mitosis
The type of cell division that allows a population of cells to increase its numbers or to maintain its numbers. The number of chromosomesremains the same in this type of cell division.
Multipotent
Having the ability to develop into more than one cell type of the body. See also pluripotent and totipotent.
N
Neural stem cell
A stem cell found in adult neural tissue that can give rise to neurons and glial (supporting) cells. Examples of glial cells include astrocytes andoligodendrocytes.
Neurons
Nerve cells, the principal functional units of the nervous system. A neuron consists of a cell body and its processes—an axon and one or more dendrites. Neurons transmit information to other neurons or cells by releasing neurotransmitters at synapses.
O
Oligodendrocyte
A supporting cell that provides insulation to nerve cells by forming a myelin sheath (a fatty layer) around axons.
P
Passage
In cell culture, the process in which cells are disassociated, washed, and seeded into new culture vessels after a round of cell growth andproliferation. The number of passages a line of cultured cells has gone through is an indication of its age and expected stability.
Pluripotent
Having the ability to give rise to all of the various cell types of the body. Pluripotent cells cannot make extra-embryonic tissues such as the amnion, chorion, and other components of the placenta. Scientists demonstrate pluripotency by providing evidence of stable developmental potential, even after prolonged culture, to form derivatives of all three embryonic germ layers from the progeny of a single cell and to generate ateratoma after injection into an immunosuppressed mouse.
Polar Body
A polar body is a structure produced when an early egg cell, or oogonium, undergoes meiosis. In the first meiosis, the oogonium divides itschromosomes evenly between the two cells but divides its cytoplasm unequally. One cell retains most of the cytoplasm, while the other gets almost none, leaving it very small. This smaller cell is called the first polar body. The first polar body usually degenerates. The ovum, or larger cell, then divides again, producing a second polar body with half the amount of chromosomes but almost no cytoplasm. The second polar body splits off and remains adjacent to the large cell, or oocyte, until it (the second polar body) degenerates. Only one large functional oocyte, or egg, is produced at the end of meiosis.
Proliferation
Expansion of the number of cells by the continuous division of single cells into two identical daughter cells.
R
Regenerative medicine
A field of medicine devoted to treatments in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cell populations or tissues. (See also cell-based therapies).
S
Signals
Internal and external factors that control changes in cell structure and function. They can be chemical or physical in nature.
Somatic cell
Any body cell other than gametes (egg or sperm); sometimes referred to as “adult” cells. See also Gamete.
Somatic (adult) stem cells
A relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation. Such cells vary in their differentiation capacity, but it is usually limited to cell types in the organ of origin. This is an active area of investigation.
Stem cells
Cells with the ability to divide for indefinite periods in culture and to give rise to specialized cells.
Stromal cells
Connective tissue cells found in virtually every organ. In bone marrow, stromal cells support blood formation.
Subculturing
Transferring cultured cells, with or without dilution, from one culture vessel to another.
Surface markers
Proteins on the outside surface of a cell that are unique to certain cell types and that can be visualized using antibodies or other detection methods.
T
Telomere
The end of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way. A telomere counteracts the tendency of the chromosome to shorten with each round of replication.
Teratoma
A multi-layered benign tumor that grows from pluripotent cells injected into mice with a dysfunctional immune system. Scientists test whether they have established a human embryonic stem cell (hESC) line by injecting putative stem cells into such mice and verifying that the resulting teratomas contain cells derived from all three embryonic germ layers.
Tetraploid complementation assay
An assay that can be used to test a stem cell’s potency. Scientists studying mouse chimeras (mixing cells of two different animals) noted that fusing two 8-cell embryos produces cells with 4 sets of chromosomes (tetraploid cells) that are biased toward developing into extra-embryonic tissues such as the placenta. The tetraploid cells do not generate the embryo itself; the embryo proper develops from injected diploid stem cells. This tendency has been exploited to test the potency of a stem cell. Scientists begin with a tetraploid embryo. Next, they inject the stem cells to be tested. If the injected cells are pluripotent, then an embryo develops. If no embryo develops, or if the resultant embryo cannot survive until birth, the scientists conclude that the cells were not truly pluripotent.
Totipotent
Having the ability to give rise to all the cell types of the body plus all of the cell types that make up the extraembryonic tissues such as the placenta. (See also Pluripotent and Multipotent).
Transdifferentiation
The process by which stem cells from one tissue differentiate into cells of another tissue.
Trophectoderm
The outer layer of the preimplantation embryo in mice. It contains trophoblast cells.
Trophoblast
The outer cell layer of the blastocyst. It is responsible for implantation and develops into the extraembryonic tissues, including the placenta, and controls the exchange of oxygen and metabolites between mother and embryo.
U
Undifferentiated
A cell that has not yet developed into a specialized cell type.
