Stem Cell Glossary

Adult Stem Cells
Stem cells found in different tissues of the developed adult. These stem cells can give rise to specialized cell types of the tissue from which they came, i.e., a heart stem cell can give rise to a functional heart muscle cell.
A very early embryo consisting of approximately 150 cells. The blastocyst is a spherical cell mass produced by cleavage of the zygote (fertilized egg). It contains a fluid-filled cavity (blastocoel), a cluster of cells called the inner cell mass (from which embryonic stem cells are derived) and another layer of cells called the trophoblast (that forms the placenta).
Cell-Based Therapies
Treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cells.
Cell Culture
The practice of growing and maintaining cells in a controlled environment under specific conditions for experimental research.
Cell Division
Method by which a single cell divides to create two cells. There are two main types of cell division: mitosis and meiosis.
Cell Type
A specific subset of cells within the body, defined by their appearance, location, and function.
To generate identical copies of a cell or organism. When used to refer to cells grown in a tissue culture dish, a clone is a population of identical cells that create a cell line. This cloned cell line is produced by cell division (mitosis) of the original cell.
A cluster or group of cells. Stem cells grow in colonies since they are unable to survive as single cells. When passaging stem cells, scientists must break up the colonies into smaller pieces in order for them to continue to grow. If colonies are broken into single cells they will be unable to survive.
Culture Medium
The liquid that covers cells in a culture dish that contains nutrients to feed the cells. Medium may also include other growth factors added to produce desired changes in the cells. Cells need to be fed because they consume the nutrients and release metabolic waste into the culture medium. Stem cells require special attention and must be fed with fresh medium daily.
Directed Differentiation
Directed differentiation is a step by step process by which scientists manipulate and guide human pluripotent stem cells to become a specific group of specialized cells. This is accomplished by controlling the environment, modifying the culture conditions and addition or omission of growth factors.
Deoxyribonucleic acid, a chemical found primarily in the nucleus of cells. DNA carries the genetic instructions for making all the structures and materials the body needs to function.
The outer of three germ layers of the early embryo. The ectoderm gives rise to the skin, nervous system, enamel of the teeth, lens of the eye, sensory organs, and related structures.
In humans, the developing organism from the time of fertilization until the end of the eighth week of gestation, when it is then called a fetus.
Embryoid Bodies
Spherical colonies seen in culture produced by the growth of embryonic stem cells in suspension. Embryoid bodies are of mixed cell types, and the distribution and timing of the appearance of specific cell types corresponds to that observed within the embryo.
The inner of three germ layers of the early embryo that gives rise in later development to tissues such as the lungs, intestine, liver, and pancreas.
Feeder Layer
Cells used in co-culture to maintain pluripotent stem cells. For human embryonic stem cell cultures, typical feeder layers include mouse embryonic fibroblasts (MEFs) or human embryonic fibroblasts. Feeder layer cells are treated to prevent them from dividing when in co-culture with stem cells.
A segment of DNA found on chromosomes in the nucleus of a cell. Genes are the functional unit of heredity and direct the formation of an enzyme or other protein.
Germ Layers
Fertilization of an egg stimulates cell division, and the resulting cells are organized into three different layers, called germ layers. The three layers are the ectoderm, the mesoderm, and the endoderm.
Hematopoietic Stem Cell
A stem cell that gives rise to all red and white blood cells and platelets.
Human Embryonic Stem Cell (hES cell or hESC)
The cells derived from the inner cell mass of a developing blastocyst. An hES cell is self-renewing (can replicate itself), pluripotent (can form all cell types found in the body), and theoretically immortal.
Human Induced Pluripotent Stem (iPS) Cell
A type of pluripotent stem cell, similar to a human embryonic stem cell, induced by the introduction of certain embryonic genes into a somatic cell.
Inner Cell Mass (ICM)
A small group of cells attached to the wall of the blastocyst (the embryo at the very early stage of development that looks like a hollow ball). Embryonic stem cells are made by isolating and culturing the cells that make up the inner cell mass. In development, the inner cell mass eventually gives rise to all the organs and tissues of the future embryo and fetus, but does not give rise to extra-embryonic tissues, such as the placenta.
In vitro
Latin for “in glass;” in a laboratory dish or test tube; in an artificial environment.
In vitro Fertilization (IVF)
A technique that unites the egg and sperm in a clinical laboratory, instead of inside the female body.
The number and appearance of chromosomes in the nucleus of a cell when observed under a microscope . The preparation and study of karyotypes falls under the scientific branch of Cytogenetics. This field plays an important role in research and medicine because it allows the scientists to study genetic patterns, developmental defects and effects of toxins on cells. Scientists working with human pluripotent stem cells have to test and evaluate the karyotypes of their cells on a regular basis since abnormal cells cannot be used in research.
Mesenchymal Stem Cell
Also known as bone marrow stromal cells, mesenchymal stem cells are rare cells, mainly found in the bone marrow, that can give rise to a large number of tissue types such as bone, cartilage, fat tissue, and connective tissue.
The middle of three germ layers that gives rise in later development to such tissues as muscle, bone, blood, connective tissue, and kidneys.
The molecules and compounds (such as nutrients and growth factors) in the fluid surrounding a cell in an organism or in the laboratory. The microenvironment plays an important role in determining the characteristics of a cell.
Cell division that allows a population of cells to increase or maintain its numbers.
The study of the shape and visual appearance of cells, tissues and organs.
The ability of a single stem cell to develop into more that one cell type in the body. Multipotent stem cells can generate multiple differentiated cell types, but all within a particular tissue, organ, or physiological system. For example, blood-forming (hematopoietic) stem cells are single multipotent cells that can produce all cell types that are normal components of the blood.
A round of cell growth and proliferation in cell culture. When passaging, scientists will use an enzyme to remove the cells from the surface of a culture plate. They will then break the colonies into smaller pieces and place them into a new culture plate where they will be able to attach and continue to grow.
The ability of a single stem cell to give rise to all of the various cell types that make up the body. Pluripotent cells have the ability to become any of the three major tissue types (germ layers) in the body, but they cannot make up the so-called “extraembryonic” tissues such as the amnion, chorion, and other components of the placenta.
Pre-implantation Embryo
A fertilized egg (zygote) and all of the developmental stages up to, but not beyond the blastocyst stage.
Progenitor cells
Progenitor cells are early descendants of stem cells. Unlike stem cells, they have a limited ability to multiply or renew themselves before they become a specialized group of cells and acquire a specific function in the body. Progenitor cells are known as multipotent or oligopotent cells since they can multiply and proceed down a specific lineage or pathway. For example, progenitor cells in the blood/bone marrow lineage can give rise to a variety of blood cells but not nerve cells or kidney cells.
Expansion of cells by the continuous division of single cells into two identical daughter cells.
Regenerative Medicine
A treatment 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.
Reproductive Cloning
The goal of reproductive cloning is to create an animal being identical to the animal that donated the somatic cell nucleus. The embryo is implanted in a uterus and develops into a live being. The first animal to be created by reproductive cloning was Dolly the sheep, born at the Roslin Institute in Scotland in 1996. See also Therapeutic Cloning.
Internal and external factors that control changes in cell structure and function.
Stem Cells
Cells with the ability to divide for indefinite periods in culture and to give rise to specialized cells.
Scientists verify that they have established a pluripotent stem cell line by injecting these stem cells into mice with a dysfunctional immune system. Since the injected cells cannot be destroyed by the mouse’s immune system, they survive and form a multi-layered benign tumor called a teratoma. In this test, the teratomas serve to establish the ability of a stem cell to give rise to all cell types in the body.
Therapeutic Cloning
The goal of therapeutic cloning is to create cells that exactly match a patient. By combining a patient’s somatic cell nucleus and an egg cell with its nucleus removed, a scientist may harvest embryonic stem cells from the resulting embryo that can be used to generate tissues that match the patient’s body. This means that tissues created are unlikely to be rejected by the patient’s immune system.
A totipotent stem cell can give rise to all the cell types that make up the body, plus all of the cell types that make up the extra-embryonic tissues such as the placenta. See also Pluripotent and Multipotent.
The process by which stem cells from one tissue differentiate into cells of another tissue.
The tissue of the developing embryo responsible for implantation and formation of the placenta. In contrast to embryonic stem cells, the trophoblast does not come from the inner cell mass, but from the cells surrounding it.
Umbilical Cord Stem Cells
Stem cells collected from the umbilical cord at birth that can produce all of the blood cells in the body. Umbilical cord stem cells are similar to stem cells that reside in bone marrow, and cord blood is currently used to treat patients who have undergone chemotherapy to destroy their bone marrow due to cancer or other blood-related disorders. Efforts are being undertaken to collect umbilical cord cells and store them in freezers for later use. However, one problem is that there may not be enough umbilical cord stem cells in any one sample to transplant into an adult patient.
Undifferentiated Cell
A cell that is unspecialized and has not acquired a specific funtion in the human body.