Adipocyte ²

The functional cell type of fat, or adipose tissue, that is found throughout the body, particularly under the skin.  Adipocytes store and synthesize fat for energy, thermal regulation and cushioning against mechanical shock.

Adult (or Somatic) Stem Cell  ¹

An undifferentiated cell found in a differentiated tissue that can renew itself and differentiate (with certain limitations) to give rise to all the specialized cell types of the tissue from which it originated.  It is important to note that scientists do not agree about whether or not adult stem cells may give rise to cell types other than those of the tissue from which they originate.

Allogeneic Transplantation ²

Cell, tissue or organ transplants from one member of a species to a genetically different member of the same species.

Autologous Stem Cell ¹

A stem cell that is removed from, stored, and later given back to the same person.

Autologous Transplantation ²

Cell, tissue or organ transplants from one individual back to the same individual.  Such transplants do not induce an immune response and are not rejected.

Astrocyte ¹  

A type of supporting (glial) cell found in the nervous system.

Biomaterial ³

A material which is in whole or in part composed of living matter, such as a polymer scaffolding perfused with cells.  Biomaterials may be used as a medical device which augments or replaces natural tissue for therapeutic effect.  The combination of synthetic and living material derived from stem cells could enable the repair of heart valves, bone, cartilage and other tissues by replacing or patching the damaged parts with materials that are genetically identical to the patient, and therefore safe from immunological rejection.

Blastocoel ¹

The fluid-filled cavity inside the blastocyst, an early, preimplantation stage of the developing embryo.

Blastocyst  ¹

A preimplantation embryo of about 150 cells produced by cell division following fertilization.  The blastocyst is a sphere made up of an outer layer of cells (the trophoblast), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass).

Bone Marrow Stromal Cells ¹

A population of cells found in bone marrow that are different from blood cells.

Bone Marrow Stromal Cells (skeletal stem cells) ¹

A multipotent subset of bone marrow stromal cells able to form bone, cartilage, stromal cells that support blood formation, fat, and fibrous tissue.

Cancer Stem Cell ³

Stem cells, which make up only a very small percentage of the total tumor mass, have been found to be the source of some, and possibly most cancers.  The cancer stem cell hypothesis states that certain stem cells remain in tissues to replenish them after injury or disease, yet because they are self-renewing and can survive for a longer period of time, the adult stem cells can also accumulate mutations which would cause them to spin off cells that divide uncontrollably, forming a tumor.  Since current cancer treatments reduce tumor mass but might not affect the stem cells seeding the tumor, new therapeutic strategies may be directed at the cancer-causing stem cells.

Cardiomyocytes ²

The functional muscle cell type of the heart that allows it to beat continuously and rhythmically.

Cell-Based Therapies ¹

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 ¹

Growth of cells in vitro in an artificial medium for research or medical treatment.

Cell Division ¹

Method by which a single cell divides to create two cells.  There are two main types of cell division: mitosis and meiosis.

Cell Line ²

Cells that can be maintained and grown in culture and display an immortal or indefinite life span.

Cell Type ²

A specific subset of cells within the body, defined by their appearance, location and function.

Chondrocyte ²

The functional cell type that makes cartilage for joints, ear canals, trachea, epiglottis, larynx, the discs between vertebrae and the ends of ribs.

Chromosome ¹

A structure consisting of DNA and regulatory proteins found in the nucleus of the cell.  The DNA in the nucleus is usually divided up among several chromosomes.  The number of chromosomes in the nucleus varies depending on the species of the organism.  Humans have 46 chromosomes. 

Clone¹

(v) To generate identical copies of a region of a DNA molecule or to generate genetically identical copies of a cell, or organism; (n) The identical molecule, cell, or organism that results from the cloning process.

1.       In reference to DNA: To clone a gene, one finds the region where the gene resides on the DNA and copies that section of the DNA using laboratory techniques.

2.       In reference to cells grown in a tissue culture dish: a clone is a line of cells that is genetically identical to the originating cell.  This cloned line is produced by cell division (mitosis) of the original cell.

3.       In reference to organisms: Many natural clones are produced by plants and (mostly invertebrate) animals.  The term clone may also be used to refer to an animal produced by somatic cell nuclear transfer (SCNT) or parthenogenesis. 

Cord Blood ³

Stem cells can be derived from blood in the umbilical cord at the time of birth.  Umbilical cord stem cells are rich in hematopoietic stem cells, which normally reside in the bone marrow and can be used for the treatment of leukemia and other blood diseases.  Numerous public and private cord banks have emerged to collect and store neonatal cord blood as future “insurance” against diseases that might be treatable using a stem cell approach.

Cord Blood Stem Cells

See Umbilical Cord Blood Stem Cells.

Culture Medium ¹

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.

Cytoplasm ²

The part of the cell not including the nucleus.

Developmental Biology³

The study of the process by which organisms grow and develop, including the formation and specialization of cells and tissues, from embryo to adulthood.  Modern research in developmental biology examines the processes of cell growth and differentiation, and the roll in which stem cells seed and control the development of tissues and organs.

Dedifferentiation ³

The process by which a cell reverts to a less specialized, progenitor state.

Differentiation ¹

The process whereby an unspecialized 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 Differentiation¹

The manipulation of stem cell culture conditions to induce differentiation into a particular cell type.

DNA ¹

Deoxyribonucleic acid, a chemical found primarily in the nucleus of cells.  DNA carries the instructions or blueprint for making all the structures and materials the body needs to function.  DNA consists of both genes and non-gene DNA in between the genes.

Ectoderm ¹

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.

Embryo ¹

In humans, the developing organism from the time of fertilization until the end of the eighth week of gestation, when it is called a fetus.

Embryoid Bodies¹

Rounded collections of cells that arise when embryonic stem cells are cultured in suspension.  Embryoid bodies contain cell types derived from all 3 germ layers.

Embryonic Germ Cells¹

Pluripotent stem cells that are derived from early germ cells (those that would become sperm and eggs).  Embryonic germ cells (EG cells) are thought to have properties similar to embryonic stem cells.

Embryonic Stem Cells ¹

Primitive (undifferentiated) cells derived from a 5-day preimplantation embryo that are capable of dividing without differentiating for a prolonged period in culture, and are known to develop into cells and tissues of the three primary germ layers.

Embryonic Stem Cell Line ¹

Embryonic stem cells, which have been cultured under in vitro conditions that allow proliferation without differentiation for months to years.

Endoderm ¹

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 ¹

Having had its nucleus removed.

Epigenetic ¹

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.

Feeder Layer ¹

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.

Fertilization ¹

The joining of the male gamete (sperm) and the female gamete (egg).

Fetus ¹

In humans, the developing human from approximately eight weeks after conception until the time of its birth.

Fibroblast ²

A connective or support cell found within most tissues of the body.  Fibroblasts provide an instructive support scaffold to help the functional cell types of a specific organ perform correctly.

Gamete ¹

An egg (in the female) or sperm (in the male) cell.  See also Somatic Cell.

Gastrulation ¹

The process cells proliferate and migrate within the embryo to transform the inner cell mass of the blastocyst stage into an embryo containing all three primary germ layers.

Gene ¹

A functional unit of heredity that is a segment of DNA found on chromosomes in the nucleus of a cell.  Genes direct the formation of an enzyme or other protein.

Germ Layers ¹

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 endoderm.

Hematopoietic Stem Cell ¹

A stem cell that gives rise to all red and white blood cells and platelets.

Heterologous ²

Not homologous or uniform.  In the context of cells, heterologous is a mixed or divergent cell population or of a divergent origin.

Histocompatible ²

A tissue or organ from a donor (the person giving the organ or tissue) that will not be rejected by the recipient (the patient in whom the tissue or organ is transplanted).  Rejection is caused because the immune system of the recipient sees the transplanted organ or tissue as foreign and tries to destroy it.  Tissues from most people are not histocompatible with other people.  In siblings, the probability of histocompatibility is higher, while identical twins are almost always histocompatible.

Homologous ²

Similar or uniform, often used in the context of genes and DNA sequences.  In the context of stem cells, the term homologous recombination is a technique used to disable a gene in embryonic stem cells.

Homologous Recombination ²

A technique used to inactivate a gene and determine its function in a living animal.  The process of homologous recombination is more efficient in embryonic stem cells than in other cell types.  It is achieved by introducing a stretch of DNA that is similar or identical (homologous) to part of a gene and to some of the DNA surrounding the gene, but different (not homologous) to a specific section of the gene.  The DNA is then introduced into the stem cells and the stretch of homologous DNA will recognize the similar sequences of the gene within the cell, and replace it.  But the cell is then left with a piece of DNA in the gene that has the wrong sequence and this interrupts the function of the gene.  The gene is then said to be knocked out.   From these embryonic stem cells, an entire mouse can be made by injecting the altered stem cells into a blastocyst, and implanting the blastocyst into a female mouse.  This is one way to make genetically manipulated mice and other animals with altered gene function.  These experiments are crucial to understand how specific genes work and interact in living animals.

Human Embryonic Stem Cell (hESC) ¹

A type of Pluripotent stem cell derived from the inner cell mass (ICM) of the blastocyst.

Hepatocyte ²

The functional cell type of the liver that makes enzymes for detoxifying metabolic waste, destroying red blood cells and reclaiming their constituents, and the synthesis of proteins for the blood plasma.

Induced Pluripotent Stem Cell (iPSC) ¹

A type of Pluripotent stem cell, similar to an embryonic stem cell, formed by the introduction of certain embryonic genes into a somatic cell.

Inner Cell Mass (ICM)¹

The cluster of cells inside the blastocyst.  These cells give rise to the embryo and ultimately the fetus.  The ICM cells are used to generate embryonic stem cells.

In Vitro ¹

Latin for “in glass”; in a laboratory dish or test tube; an artificial environment.

In Vitro Fertilization ¹

A technique that unites the egg and sperm in a laboratory instead of inside the female body.

In Vivo ³

Latin for “within the living,” the term in vivo refers to experiments conducted using a whole, living organism.  In vivo experimentation is often necessary to confirm hypotheses that cannot be thoroughly tested in the artificial environment of laboratory glassware.  In vivo research, which can be conducted in animals or controlled human clinical trials, provide more complete information on the overall effects of a disease or its treatment.

Islet Cell ²

The functional cell of the pancreas that is responsible for secreting insulin, glucogon, gastrin and somatostatin.  Together, these molecules regulate a number of processes including carbohydrate and fat metabolism, blood glucose levels and acid secretions into the stomach.

Long-Term Self-Renewal ¹

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.

Mesenchymal Stem Cells ¹

A term that is currently used to define non-blood adult cells from a variety of tissues, although it is not clear that mesenchymal stem cells from different tissues are the same.

Meiosis ¹

The type of cell division a diploid germ cell undergoes to produce gametes (sperm or eggs) that will carry half the normal chromosome number.  This is to ensure that when fertilization occurs, the fertilized egg will carry the normal number of chromosomes rather than causing aneuploidy (an abnormal number of chromosomes).

Mesoderm ¹

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 ¹

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 ¹

The type of cell division that allows a population of cells to increase its numbers or to maintain its numbers.  The number of chromosomes remains the same in this type of cell division.

Morphology ²

Study of the shape and visual appearance of cells, tissues and organs.

Multipotent ¹

Having the ability to develop into more than one cell type of the body.  See also Pluripotent and totipotent.

Multipotent Stem Cells²

Stem cells whose progeny are of 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.

Myocyte ²

The functional cell type of muscles.

Neural Stem Cell ¹

A stem cell found in adult neural tissue that can give rise to neurons and glial (supporting) cells.  Examples of glial cells include astrocytes and oligodendrocytes.

Neurons ¹

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.

Nucleus ²

A part of the cell, situated more or less in the middle of the cell, that is surrounded by a specialized membrane and contains the DNA of the cell.  This DNA is packaged into structures called chromosomes, which is the genetic, inherited material of cells.

Oligodendrocyte ¹

A supporting cell that provides insulation to nerve cells by forming a myelin sheath (a fatty layer) around axons.

Oligopotent Progenitor Cells ²

Progenitor cells that can produce more than one type of mature cell.  An example is the myeloid progenitor cell which can give rise to mature blood cells, including blood granulocytes, monocytes, red blood cells, platelets, basophiles, eosinophiles and dendritic cells, but not T lymphocytes, B lymphocytes, or natural killer cells.

Osteoblast ²

The functional cell type responsible for making bone.

Parthenogenesis ¹

The artificial activation of an egg in the absence of a sperm; the egg begins to divide as if it has been fertilized.

Passage ¹

In cell culture, the process in which cells are disassociated, washed, and seeded into new culture vessels after a round of cell growth and proliferation.  The number of passages a line of cultured cells has gone through is an indication of its age and expected stability.

Phenotype ²

The description of the characteristics of a cell, a tissue or an animal; as black and white fur of a mouse are two phenotypes that can be found.  The phenotype is determined by the genes (or the genotype) and by the environment.  For example, short stature is a phenotype that can be genetically determined (and therefore inherited from the parents), but can also be caused by malnourishment during childhood (and therefore be caused by the environment).

Plasticity  

The ability of stem cells from one adult tissue to generate the differentiated cell types of another tissue.

Pluripotent ¹

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 a teratoma after injection into an immunosuppressed mouse.

Polar Body ¹

A polar body is a structure produced when an early egg cell, or oogonium, undergoes meiosis.  In the first meiosis, the oogonium divides its chromosomes 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.

Preimplantation ¹

With regard to an embryo, preimplantation means that the embryo has not yet implanted in the wall of the uterus.  Human embryonic stem cells are derived from preimplantation-stage embryos fertilized outside a woman’s body (in vitro).

Progenitor Cell ²

A progenitor cell, often confused with stem cell, is an early descendant of a stem cell that can only differentiate, but it cannot renew itself anymore.  In contrast, a stem cell can renew itself (make more stem cells by cell division) or it can differentiate (divide and with each cell division evolve more and more into different types of cells).  A progenitor cell is often more limited in the kinds of cells it can become than a stem cell.  In scientific terms, it is said that progenitor cells are more differentiated than stem cells.

Proliferation ¹

Expansion of the number of cells by the continuous division of single cells into two identical daughter cells.

Protein Marker ³

Stem cells, like most cells, display a characteristic set of protein molecules on their cell surface called markers, which can be used to make a preliminary identification.  Using fluorescently tagged antibodies that attach to these markers, an instrument called a fluorescence activated cell sorter (FACS) can separate and isolate the rare stem cell among a population of thousands of differentiated cells.

Regenerative Medicine¹

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).

Reproductive Cloning¹

The process of using somatic cell nuclear transfer (SCNT) to produce a normal, full grown organism (e.g., animal) genetically identical to the organism (animal) that donated the somatic cell nucleus.  In mammals, this would require implanting the resulting embryo in a uterus where it would undergo normal development to become a live independent 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 Somatic Cell Nuclear Transfer (SCNT).

Signals ¹

Internal and external factors that control changes in cell structure and function.  They can be chemical or physical in nature.

Somatic Cell ¹

Any body cell other than gametes (egg or sperm); sometimes referred to as “adult” cells.  See also Gamete.

Somatic Cell Nuclear Transfer (SCNT) ¹

A technique that combines an enucleated egg and the nucleus of a somatic cell to make an embryo.  SCNT can be used for therapeutic or reproductive purposes, but the initial stage that combines an enucleated egg and a somatic cell nucleus is the same.  See also Therapeutic Cloning and Reproductive Cloning.

Somatic (Adult) Stem Cells ¹

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 Cell Homing ³

The migration of stem cells through the blood or tissue to an ultimate destination where it differentiates and replaces or builds tissue.  Stem cell homing is triggered by interactions between the cell surface adhesion molecules (such as selectins, integrins and ICAMs)and the cell’s surrounding environment.

Stem Cells ¹

Cells with the ability to divide for indefinite periods in culture and to give rise to specialized cells.

Stromal Cells ¹

Connective tissue cells found in virtually every organ.  In bone marrow, stromal cells support blood formation.

Subculturing ¹

Transferring cultured cells, with or without dilution, from one culture vessel to another.

Surface Markers ¹

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.

Teratoma ¹

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 ¹

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.

Therapeutic Cloning ¹

The process of using somatic cell nuclear transfer (SCNT) to produce cells that exactly match a patient.  By combining a patient’s somatic cell nucleus and an enucleated egg, a scientist may harvest embryonic stem cells from the resulting embryo that can be used to generate tissues that match a patient’s body.  This means the tissues created are unlikely to be rejected by the patient’s immune system.  See also Somatic Cell Nuclear Transfer (SCNT).

Totipotent ¹

Having the ability to give rise to all the cell types of the body plus all of the cell types that make up the extra-embryonic tissues such as the placenta. (See also Pluripotent and Multipotent)

Totipotent Stem Cells ²

Stem cells than can give rise to all cell types that are found in an embryo, fetus, or developed organism, including the embryonic components of the trophoblast and placenta required to support development and birth.  The zygote and the cells at the very early stages following fertilization (i.e., the 2-cell stage) are considered totipotent.

Transdifferentiation ¹

The process by which stem cells from one tissue differentiate into cells of another tissue.

Translational Medicine³

The area of focus or effort to transition basic research discoveries into clinical applications that benefit patients.

Transplantation Biology²

The science that studies the transplantation of organs and cells.  Transplantation biologists investigate scientific questions to understand why foreign tissues and organs are rejected, the way transplanted organs function in the recipient, how this function can be maintained or improved, and how the organ to be transplanted should be handled to obtain optimal results.

Trophectoderm ¹

The outer cell layer of the blastocyst.  It is responsible for implantation and develops into the extra-embryonic tissues, including the placenta, and controls the exchange of oxygen and metabolites between mother and embryo.

Umbilical Cord Blood Stem Cells ¹

Stem cells collected from the umbilical cord at birth that can produce all of the blood cells in the body (hematopoietic).  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.

Undifferentiated ¹

A cell that has not yet developed into a specialized cell type.

Unipotent Stem Cells ²

Stem cells that self-renew as well as give rise to a single mature cell type; e.g., spermatogenic stem cells.

Zygote ²

The cell that results from the union of sperm and egg during fertilization.  Cell division begins after the zygote forms.