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Adult Stem Cell: See Somatic Stem Cell

Astrocyte: a type of supporting (glial) cell found in the nervous system.∗

Blastocyst: A preimplantation embryo of about 150 cells produced by cell division (mitosis) following fertilization. The blastocyst is a sphere made up of an outer layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass), from which embryonic stem cells are derived.∗≡

Bone Marrow Stromal Cells: see Mesenchymal Stem Cells.

Cancer Stem Cell: Self-renewing cell responsible for sustaining a cancer and for producing differentiated progeny that form the bulk of the cancer. Cancer stem cells are not associated with all cancers.Δ≡

Cell Culture: Growth of cells in vitro in an artificial medium for experimental research.∗

Cell Division: The method by which a single cell divides to create two cells. There are two main types of cell division: mitosis and meiosis.∗

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

Cell-based Therapy: Treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cells or tissues.∗

Chimera: An organism composed of cells derived from at least two genetically different organisms. The cells could be from the same or separate species.•≡

Chromatin: The combination of DNA and the proteins coating the DNA. These proteins consist mainly of histones, around which the DNA is wrapped.

Chromosome: A piece of DNA organized around proteins. Humans have 46 chromosomes, inheriting 23 from each parent.

Clone: as a verb, to clone is to generate identical copies of a molecule, cell, or organism. As a noun, there are two common definitions:

  1. When it is used to refer 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 mitosis of the originating cell.
  2. The term clone may also be used to refer to an animal produced by somatic cell nuclear transfer (SCNT), for example Dolly the sheep.∗≡

Cloning: See Somatic Cell Nuclear Transfer (SCNT).

Cord Blood Stem Cell: A stem cell collected from the umbilical cord at birth that can produce all of the blood (hematopoietic) cells in the body. 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.∗

Cytoplasm: The contents of a cell other than the nucleus; cytoplasm consists of a fluid containing numerous structures, known as organelles, that carry out essential cell functions.∗

Differentiation: The process whereby an undifferentiated cell acquires the features of a specialized cell such as a heart, liver, or muscle cell.∗

Directed Differentiation: Manipulating stem cell culture conditions to induce differentiation into a particular cell type.∗

DNA: 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.∗

Ectoderm: 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: In humans, the developing organism from the time of fertilization until the end of the eighth week of gestation, after which it is called a fetus.∗

Embryoid Bodies: Spheroid colonies produced when embryonic stem cells are grown in suspension. Embryoid bodies contain a variety of cell types derived from differentiation of the embryonic stem cells.±≡

Embryonic Germ Cell: Pluripotent stem cell that is 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 Cell (ESC): Primitive (undifferentiated) cell derived from a preimplantation embryo (up to nine days after fertilization in humans) that has the potential to become a wide variety of specialized cell types. ESCs are self-renewing (can replicate themselves), pluripotent (can form all cell types found in the body), and can divide indefinitely in culture.∗±≡

Embryonic Stem Cell Line: Embryonic stem cells that have been cultured under in vitro conditions allowing proliferation without differentiation for months to years.∗

Endoderm: 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: A cell with its nucleus removed.∗

Epiblast Stem Cell (EpiSC): A type of stem cell derived from an early post-implantation mouse embryo (epiblast) that has some properties of embryonic stem cells, but not the level of pluripotency associated with embryonic stem cells. EpiSCs are cultured under the same conditions required for human embryonic stem cell culture.

Epigenetics: Heritable changes in chromatin structure that are not changes in the DNA code. Generally, epigenetics refers to stable silencing or opening of regions of the genome by winding or unwinding the DNA around histones. This prevents or allows access of transcription factors, stimulating expression of specific genes.

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

Fetus: A developing human from approximately eight weeks after conception, corresponding to formation of the major organ systems, until the time of its birth.∗≡

Gamete: An egg cell or oocyte in females, or a sperm cell in males.∗≡

Gene: 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 enzymes or other proteins.∗

Germ Layers: After the blastocyst stage of development, the inner cell mass organizes into three distinct cell 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 (hESC): A type of pluripotent stem cell derived from the inner cell mass (ICM) of a preimplantation human embryo.∗≡

Implantation: The process by which the embryo attaches itself to the wall of the maternal uterus, enabling growth beyond the blastocyst.

In Vitro: Latin for "in glass"; in a laboratory dish or test tube; an artificial environment.∗

In Vitro Fertilization: A technique that unites the egg and sperm in a laboratory, instead of inside the female body.∗

Induced Pluripotent Stem (iPS) Cell: A form of pluripotent stem cell that is created in the laboratory by reprogramming differentiated cells into an embryonic stem cell-like state by forced expression of proteins.♦≡

Inner Cell Mass (ICM): The cluster of cells inside the blastocyst. These cells give rise to the embryo and ultimately the fetus. The inner cell mass cells are used to generate embryonic stem cells.∗

Meiosis: Cell division without preceding genome duplication resulting in cells with half the number of chromosomes normally present in the adult of the species. In contrast to mitosis, this cell division produces gametes. Meiosis ensures that fertilization restores the full number of chromosomes in the embryo, rather than causing aneuploidy, or an abnormal number of chromosomes.∗≡

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 (the lining of joints), fat tissue, and connective tissue (tissue that is in between organs and structures in the body).±

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.∗

Mitosis: Cell division following duplication of the genome and resulting in two daughter cells with an even segregation of the genetic material. Mitosis allows a population of cells to increase or, in the case of cell death, maintain their number.∗

Morula: A solid mass of 16-32 cells that resembles a mulberry and results from the cleavage (cell division without growth) of a zygote (fertilized egg).•

Multipotent: Ability of a single stem cell to develop into more than one cell type of the body. (See also pluripotent and totipotent.)∗

Neural Stem Cell: A stem cell found in adult neural tissue that can give rise to neurons and glial (supporting) cells.∗

Neurons: Nerve cells, the structural and functional unit of the nervous system. A neuron consists of a cell body and its processes�an axon and one or more dendrites. Neurons function by starting and conducting impulses. Neurons transmit impulses to other neurons or cells by releasing neurotransmitters at synapses.∗

Nucleus: Part of the cell containing the DNA, in the form of chromosomes, separated from the cytoplasm by a membrane.

Parthenogenesis: Artificial activation of an egg in the absence of a sperm; the egg is "tricked" into behaving as if it has been fertilized.∗

Plasticity: The notion that somatic stem cells from one tissue can generate the differentiated cell types of another tissue.∗≡

Pluripotent: The ability of a single stem cell to give rise to all of the various cell types that make up the body. Pluripotent cells cannot make so-called "extra-embryonic" tissues such as the amnion, chorion, and other components of the placenta.∗≡

Preimplantation: 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). Human embryos implant between eight and nine days after fertilization.∗

Postimplantation: The period of development between implantation of the embryo and establishment of the body plan of a developed organism with identifiable tissues and organs.±≡

Proliferation: Expansion of cells by the continuous division of single cells into two identical daughter cells.∗

Regenerative Medicine: The use of biological agents, for example stem cells, to treat diseases and 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.∗ [NOTE: The Empire State Stem Cell Board statute specifically prohibits support for research that directly or indirectly involves human reproductive cloning.]

Reprogramming: The process of converting a differentiated cell to an embryonic stem cell-like state by the forced expression of proteins important for maintaining the �stemness" of embryonic stem cells. Used, for example, to generate induced pluripotent stem (iPS) cells. Alternatively, reprogramming can be described as a switch in gene expression from one kind of cell to another unrelated cell type. For example, switching of adult pancreatic exocrine (non-insulin producing) cells to pancreatic β-cells that secrete insulin. Reprogramming occurs naturally in regenerative organisms, such as planaria (flatworms), starfish, and salamanders, and is termed dedifferentiation.

Self-renewal: A cell division in which a stem cell divides, producing two daughter cells, one of which remains a stem cell and takes the place of the parent cell, while the other can differentiate. This is a defining property of stem cells.

Somatic Cell: Any body cell other than gametes (egg or sperm).∗

Somatic Cell Nuclear Transfer (SCNT): A technique that combines an enucleated egg (nucleus removed) and the nucleus of a somatic cell to make an embryo. SCNT has potential for the study and the treatment of diseases because it allows the programming of disease-specific somatic cells into embryonic stem cell lines.∗ ≡

Somatic (or Adult) Stem Cell: An undifferentiated cell found in a differentiated tissue that can renew itself and differentiate (with certain limitations) into all the specialized cell types of the tissue from which it originated. Somatic stem cells are thought to be important for maintenance and repair of the organ or tissue.∗

Stem Cell: A cell with the ability to divide for prolonged periods in culture and to give rise to specialized cells. Stem cells are characterized by the ability of self-renewal and potency.∗≡

Stem Cell Niche: The environmental milieu providing the support and stimuli necessary to sustain self-renewal. Niches contain soluble factors and cell-cell interactions that allow the stem cell to remain undifferentiated.

Stromal Cell: Non-blood cell derived from blood organs, such as bone marrow or fetal liver, which is capable of supporting growth of blood cells in vitro. Stromal cells that make the matrix within the bone marrow are also derived from mesenchymal stem cells.∗

Surface Marker: A protein on the outside surface of a cell that is unique to certain cell types and which is recognized using antibodies or other detection methods.∗

Therapeutic Cloning: The goal of therapeutic cloning is to create cells that genetically 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: Having the ability to give rise to all the cell types that make up the body plus all of the cell types that make up the extraembryonic tissues such as the placenta. (See also pluripotent and multipotent.)∗

Transcription Factor: A protein that turns on or shuts off specific genes.

Trophoblast: The extraembryonic tissue responsible for implantation, developing into the placenta, and controlling the exchange of oxygen and metabolites between mother and embryo.∗

Umbilical Cord Blood Stem Cell: See Cord Blood Stem Cell.

Undifferentiated: A cell that has not yet generated structures or manufactured proteins characteristic of a specialized cell type.∗

Zygote: A fertilized egg.

∗ Source: National Institutes of Health

± Source: International Society for Stem Cell Research

• Source: National Academy of Sciences

Δ Source: EuroStemCell

♦ Source: Adapted from: Baker, M. (2007) Nature Rep Stem Cells.

≡ Adapted from source