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Adipose Stem Cells - Stem cells derived from fat cells.
Adult SC/tissue - 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.
Alleles - The different DNA sequences within a gene locus are termed alleles.
Allelic heterogeneity - A single disorder, trait, or pattern of traits caused by different mutations within a gene. (See NIH glossary: Allelic Heterogeneity)
Allogeneic Transplant - A transplant in which a patient receives stem cells from someone other than themselves or their identical twin. The patient’s brother, sister, parent may be used as the donor. An unrelated person may also be used as the donor.
Altered Nuclear Transfer - Process that uses nuclear transfer to create cells that are incapable of forming a normal embryo but can generate stem cells.
Amniotic Fluid - Liquid from the amniotic sac of a pregnant woman. The amniotic sac surrounds the fetus, protecting and nourishing it. This fluid contains stem cells.
Angiogenesis- A fundamental physiological process of growth of new blood vessels from pre-existing vessels, involved in growth and development and wound healing; also stimulates tumors to change from a dormant to a malignant state because of nutrients that can be delivered by new blood vessels, leading to the use of angiogenesis inhibitors in cancer treatment.
Anti-Rejection Drugs - Daily medications taken by organ transplant patients to prevent organ rejection, by helping to suppress the immune system's response to a new organ.
Apoptosis - A natural process of self-destruction in certain cells that is determined by the genes and can be initiated by a stimulus or by removal of a repressor agent.
Autologous Transplant - A transplant in which a patient receives his or her own stem cells that have been removed or stored.


Blastocyst (blastula) - 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).
Basophil - Basophils or basophil granulocytes are about 0.01% - 0.3% of circulating white blood cells. They can be recruited out of blood into tissue when needed, for example in inflammatory and allergic reactions.
B cells - B cells are lymphocytes important to the humoral immune response. Their principal function is to make antibodies against antigens and eventually develop into memory B cells. B cells are an essential component of the adaptive immune system. Immature B cells are produced in the bone marrow of most mammals. The human body makes millions of different types (all clones) of B cells each day that circulate in the blood and lymphatic system performing the role of immune surveillance. They produce antibodies when fully activated.
Bone Marrow - Bone marrow is the soft tissue found in the interior of bones. The hematopoietic compartment of bone marrow produces approximately 500 billion blood cells per day; bone marrow is also key in the lymphatic system, producing lymphocytes for the immune system. There are two types of bone marrow: red marrow (mainly hematopoietic tissue, in flat bones), and yellow marrow (mostly fat cells, in long bones).


Cellular Differentiation - The process in which a stem cell becomes a specialized cell.
Chimera - An organism composed of cells or tissues from more than one individual or species (The National Academies).
Cholangiocytes - The epithelial cells (the cells that line the surface of a cavity) of the bile duct.
Chromatin Packaging - The packaging of DNA into chromatin allows the DNA of human cells (about 2 m in length if stretched out) to fit into a nucleus with a diameter of only 10 microns.
Chromatin modifications - Chromatin is the combination of DNA and proteins that make up the cell nucleus. The primary functions of chromatin are: package DNA into a very small volume to fit in the cell, strengthen the DNA to allow mitosis and meiosis, prevent DNA damage, and control gene expression and DNA replication. The primary protein components of chromatin are histones that act as spools around which DNA winds and compact it. Histones play a role in gene regulation, as they are subject to modification by enzymes, for example methylation, acetylation, phosphorylation, etc.
Chromosome- 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.
Cleavage arrested blastomere - A blastomere is a type of cell produced by cleavage (cell division) of the ovum after fertilization. A cleavage arrested blastomere is one where this cell division has been halted.
Clone - 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.
Cumulus Cell - Specialized cells surrounding and nourishing the oocyte. (See CopeWithCytokines: Cumulus Cell)
CD - Cluster of Differentiation or CD is a system to classify cell surface molecules on a variety of cell types. These cell surface molecules are generally proteins or glycoprotiens and often serve as receptors or ligands (the molecule that activates a receptor). As of 2011, there are about 250 numbered CD for human cells.
Cumulus Matrix - The extracellular matrix of the cumulus cell.
Cyclosporine - An immunosuppressant drug widely used in post-allogeneic organ transplant to reduce the activity of the patient's immune system, and therefore the risk of organ rejection.
Cytochalasin - Any of a group of fungal metabolites that interfere with the formation of microfilaments and thus disrupt cellular processes dependent on those filaments. (See FreeDictionary: Cytochalasin)
Cytoplasmic Hybrid - A eukaryotic cell line produced by the fusion of a whole cell with a cytoplast (an enucleated cell).


De-differentiation- The process in which a specialized cell regresses into a simpler, less specialized cell. A specialized cell can regress into an embryonic-like cell.
Demethylation- Demethylation is the removal of methyl group (CH3) from a molecule, often catalyzed by an enzyme such as one of the liver enzymes.
Dendritic cells- Dendritic cells (DCs) are immune cells whose main function is to process antigen material and present it on the surface to other cells of the immune system, acting as messengers between the innate and adaptive immune systems. They are present in tissues in contact with the external environment, such as the skin. Dendritic cells are derived from hematopoietic bone marrow progenitor cells.
Dental pulp stem cells - Dental pulp is the soft living tissue inside a tooth. Mesenchymal stem cells are found inside this tissue. Dental Pulp Stem Cells (DPSCs) are multipotent stem cells that have the potential to differentiate into a variety of cell types such as cardio myocytes, neurons, myocytes, osteocytes, chondrocytes, adipocytes.
Dermal Fibroblasts - Fibroblasts (see below) of the dermis, the layer of skin between the epidermis and subcutaneous tissues.
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.
Diploid - A complete set of chromosomes with both members of each chromosome pair. Human somatic cells are diploid.
Directed Differentiation- Manipulating stem cell culture conditions to induce differentiation into a particular cell type.
Downregulate - Downregulation is the term to describe a cell decreasing the quantity of a cellular component, such as RNA or a protein, in response to an exterior influence. Ex.: cellular decrease in the number of receptors to a molecule (e.g., a hormone or neurotransmitter), which reduces the cell's sensitivity to the molecule.
DNA Methylation - The addition of a methyl group to DNA — for example, to the number 5 carbon of the cytosine pyrimidine ring — with the specific effect of reducing gene expression. It also forms the basis of chromatin structure, which enables cells to form the myriad characteristics necessary for multicellular life from a single immutable sequence of DNA.
DNA Modification - A variety of chemical changes made to a DNA molecule just after it has been replicated. An example is DNA methylation.


Ecdtoderm - The ectoderm is one of the three primary germ cell layers of the early embryo (the other two layers are the mesoderm and endoderm. The ectoderm, the most exterior layer that emerges first and forms from the outer layer of germ cells, differentiates to form the nervous system (spine, peripheral nerves and brain), tooth enamel, the epidermis (skin), as well the lining of mouth, anus, nostrils, sweat glands, hair and nails.
Embryogenesis - The production of an embryo.
Embryoid Bodies - 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 Stem Cells - Stem cells taken from the embryo.
Endoderm - The endoderm is one of the three primary germ cell layers in the very early embryo (the other two are the ectoderm and mesoderm, with the endoderm as the innermost layer. The endoderm gives rise to most or all of the: gastrointestinal tract and parts or related organs such as the liver and pancreas, the respiratory tract, endocrine glands and organs, the auditory system and urinary system.
Enucleated - A cell that lacks a nucleus.
Eosinophils - Eosinophils,or eosinophil granulocytes, are white blood cells and immune system components that combat parasites and certain infections. They also are involved in allergic and asthmatic reactions. They develop during hematopoiesis in bone marrow, then migrate into blood.
Epiblast - The tissue type derived from the inner mass of the blastocyte.
Epigenetics- 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. (See NIH glossary: Oligodendrocyte)
Epitope A site on an antigen that is recognized by an antibody; epitopes are also called antigenic determinants. (See EverythingBio glossary: Epitope)
Excess IVF Embryos - The surplus of embryos that an IVF clinic has, which can later be used for research.


Fibroblast - A fibroblast is the most common type of cell found in connective tissue. Fibroblasts secrete collagen proteins that are used to maintain a structural framework for many tissues. They also play an important role in healing wounds. (See NIH glossary: Fibroblast)
Fluorescence-Activated Cell Sorting (FACS)* - A flow cytometer (a scientific instrument used to measure the characteristics of individual cells) that is modified for the purpose of separating (sorting) cells based on the amount of light (fluorescence) emitted by each cell. (See Medterms: FACS)
Fragmentation - The breaking apart of cells or cell organelles into smaller parts.


Gamete - An egg (in the female) or sperm (in the male) cell.
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 an enzyme or other protein.
Gastrulation - The process of forming the 3 germ layers (endoderm, mesoderm, ectoderm) that occurs when a blastula develops into a gastrula.
Genome-Wide Approach - An approach that involves rapidly scanning markers across the complete sets of DNA, or genomes, of many people to find genetic variations associated with a particular disease.
Germinal Cells - Cells in the fetus that give rise to sperm and egg.
Germline- The line of germ cells that have genetic material that may be passed to a child.
Germ layers - Endoderm, mesoderm, ectoderm.
Geron Corporation - A biotechnology company that specializes in developing and commercialization of cell-based therapies derived from human embryonic stem cells for treatment of various chronic diseases.
Global Demethylation - The process of genome-wide removal of methyl groups from nucleotide in DNA.
Graft vs. Host Disease - A common complication of allogeneic bone marrow transplantation in which functional immune cells in the transplanted marrow recognize the recipient as "foreign" and mount an immunologic attack. It can also take place in a blood transfusion under certain circumstances.


Haploid- A set of chromosomes with one member of each chromosome pair. Human gametes are haploid.
Hayflick Limit - The number of times a normal cell population will divide before it stops, presumably because the telomeres reach a critical length. Presumed to be ~50 times.
Hematopoiesis - The formation of blood cellular components. (See Wikipedia: Haematopoiesis)
Hematopoietic Stem Cells - A stem cell that gives rise to all types of blood cells.
Hematopoietic stem cell (HSC) transplant - Growing adult hematopoietic stem cells obtained from the patient in whom they will be transplanted, and transplanting the specific cell type that was cultured for specific medical benefit.
Hematopoietic system - Hematopoiesis is the formation of the cellular components of the blood, all of which are derived from haematopoietic stem cells. Approximately 1011–1012 new blood cells are produced daily in a healthy adult; this maintains steady-state levels in the peripheral circulation.
Homeobox (HOX) genes - Hox genes determine the basic structure and orientation of an organism, and are critical for normal early embryonic development of segment structures of animals such as legs and wings.
Hemimethylated DNA - Duplex DNA where only one of the two strands are methylated. It is important for regulating and protecting DNA.
Hepatocyte - A liver cell.
Heterokaryon - A cell having two or more genetically different nuclei.
High Telomerase Activity - The enzyme telomerase allows for replacement of short bits of DNA known as telomeres, which are otherwise shortened when a cell divides via mitosis. High activity can lead to cell immortality as well as unbounded growth.
Histocompatiblility- The quality of being accepted and remaining functional; said of that relationship between the genotypes of donor and host in which a graft generally will not be rejected (http://medical-dictionary.thefreedictionary.com/histocompatibility).
Histology - Histology is the study of the microscopic anatomy of cells and tissues of plants and animals, which typically are studied by sectioning and staining and examination under a light or electron microscope.
Histones- Highly alkaline proteins found in eukaryotic cell nuclei, which package and order the DNA into structural units called called nucleosomes.
HLA (Human Leukocyte Antigens)- Histocompatibility antigens found on white blood cells that serve as recognition signals to the body’s immune system that enable it to distinguish between innate and foreign material.
HLA incompatible Human leukocyte antigen (HLA) is also called major histocompatibility complex (MHC), a more universal term; HLA/MHC is a cell surface molecule that determines compatibility of donors for organ transplant as well as one's susceptibility to autoimmune disease. When there is HLA incompatibility, tissues of the donor and the recipient are immuno-incompatible.
Homeobox (HOX) genes - Hox genes determine the basic structure and orientation of an organism, and are critical for normal early embryonic development of segment structures of animals such as legs and wings
Homologous Genetic Recombination - The exchange of a segment of DNA between two homologous chromosomes during meiosis leading to a novel combination of genetic material in the offspring. (http://ghr.nlm.nih.gov/glossary=geneticrecombination)
Homologous Genetic Recombination - The exchange of a segment of DNA between two homologous chromosomes during meiosis leading to a novel combination of genetic material in the offspring. (http://ghr.nlm.nih.gov/glossary=geneticrecombination)
Human Embryology - The study of the development of the human embryo
Human Embryonic Stem Cell (hESC) Lines - Embryonic stem cells, which have been cultured under in vitro conditions that allow proliferation without differentiation for months to years.
Human Telomerase Reverse Transcriptase- A catalytic subunit of the enzyme telomerase.
Hybridoma - A cell that is produced in the laboratory from the fusion of an antibody-producing lymphocyte and a nonantibody-producing cancer cell, usually a myeloma or lymphoma. It proliferates and produces a continuous supply of a specific monoclonal antibody. (See FreeDictionary: Hybridoma)
Hypoxanthine - A purine base formed as an intermediate in the degradation of purines and purine nucleosides to uric acid and in the salvage of free purines. Complexed with ribose it is inosine.( http://medical-dictionary.thefreedictionary.com/hypoxanthine)


Immunoglobulins (IgM, IgG, IgA, IgE, IgD) - An immunoglobulin, or anti-body, is a large Y-shaped protein produced by the B-cells of the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique antigen of the foreign target.
In silico - A term referring to processes done using computers or via computer simulation. In biology, it can refer to using computer models to screen for new drugs.
In situ - Examining something in the exact place where it occurs.
Immunohistochemistry - Immunohistochemistry (IHC) refers to detecting antigens (e.g., proteins) in cells of a tissue section, using antibodies that bind to specific antigens.
In vitro - Refers to an experiment done in a Petri dish or a test tube.
In vivo- Experiments performed in a living organism.
Inner Cell Mass - 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.
Insertional Mutagenesis - Mutagenesis of DNA by the insertion of one or more bases.
Ionophore - A lipid-soluble molecule usually synthesized by microorganisms to transport ions across the lipid bilayer of the cell membrane
iPS - A type of pluripotent stem cell, similar to an embryonic stem cell, formed by the introduction of certain embryonic genes into a somatic cell. (See NIH glossary: Embryo)
Interventional research - Research conducted via a planned, active intervention or treatment designed to test a hypothesis; there will be one or more conditions or treatment arms to the study, plus a control or placebo condition.
IVF (in vitro fertilization) - In vitro fertilisation (IVF) is a procedure in fertility medicine when natural conception fails. Human egg cells (ova) are harvested, fertilized by sperm outside the body, in vitro (i.e., in a Petri dish), and the resulting embryos are transferred to the patient's uterus in hopes of a pregnancy.


Lineage Reprogramming - Reprogramming terminally differentiated cellular lineages back to stem cells permits regeneration of a multipotent self-lineage of stem cells.
Locus- The location of a gene on a chromosome region is called a locus.
Lymphocyte - A lymphocyte is a type of white blood cell in the immune system of vertebrates. There are many types of lymphocytes (e.g., natural killer cells (NK cells), T cells and B cells).


Macrophages- Macrophages are immune cells for both non-specific defense (innate immunity) and to help initiate specific immune defense mechanisms (adaptive immunity) in vertebrates. They phagocytose (engulf, then digest) cellular debris and pathogens, and also stimulate lymphocytes and other immune cells to respond to pathogens.
Major histocompatibility complex (MHC) genes - Genes that control HLA proteins- see HLA.
Mammary Epithelial Cells- Epithelial cells are cells that cover the surface of the body and line its cavities. Mammary epithelial cells are those located in the breast.
Mast cells - Mast cells occur in several types of tissues. They secrete histamine and heparin, involved in allergy and anaphylaxis, and also play an important role in wound healing and defense against pathogens.
Meiosis - 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).
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. (See NIH glossary: Oligodendrocyte)
Mesoangioblast - Blood vessel derived stem cell.
Mesoderm - The mesoderm is the middle of the three primary germ cell layers in the very early embryo (along with ectoderm (outside layer) and endoderm (inside layer)). It forms muscle, connective tissue and other tissues.
Metabolomics - The study of biological substances that are end products of metabolic pathways. These metabolites provide a chemical fingerprint of various cellular processes occurring in a cell.
Methyltransferase - A type of transferase enzyme that transfers a methyl group from a donor to an acceptor. Involved in DNA methylation
Mitosis - 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.
Monoclonal Antibody - Any of a class of highly specific antibodies produced by the clones of a single hybrid cell formed in the laboratory by the fusion of a B cell with a tumor cell and widely used in medical and biological research. (See FreeDictionary: Moniclonal Antibody)
Monocytes - A type of white blood cell that replenishes macrophages and dentritic cells.
Morula- The cells in the zygote divide to form a compact ball of cells called the morula.
miRNAs - miRNA is short for microRNA, a short ribonucleic acid (RNA) molecule found in eukaryotic cells. miRNAs are post-transcriptional regulators that are involved in gene silencing.
mRNAs - Messenger RNA (mRNA) is a molecule of RNA that encodes a chemical "blueprint" for a protein product. mRNA carries coding information to sites of protein synthesis, ribosomes.
Multipotent progenitors (MPPs) - A stem cell also is a progenitor cell, one that is totipotent to multipotent, i.e., can differentiate into many kinds of cells. The typical non-SC progenitor cell can divide only a limited number of times, and will differentiate into its "target" cell. Sometimes progenitor cells are described as oligopotent.
Multipotent Stem Cells- Cells that can differentiate into a more limited number of unique cells. For example, a hematopoietic cell is a multipotent blood stem cell type that can develop into several types of blood cells, but cannot develop into brain cells or other types of cells. However, it is being discovered that their plasticity is greater that originally thought.
Murine - Pertaining to the taxonomic Family Muridae, the true rats and mice; as in "murine model" in animal experimentation.
Myeloma Cells - A tumor composed of cells of the type normally found in the bone marrow. (See FreeDictionary: Plasma Cell Myeloma)


Neonatal- Of or relating to newborn infants or an infant.
Neovascularization - Neovascularization is the formation of functional microvascular networks with red blood cell perfusion (angiogenesis involves capillary sprouting from pre-existing blood vessels).
Neurogenesis - The process of generating neurons.
Nuclear Transfer- Technique in which nuclear genetic material from a patient’s own cell is isolated and then transferred into an enucleated.
Neutrophils - Neutrophils (neutrophil granulocytes) are the most numerous type of white blood cells in mammals, and an essential component of the innate immune system. There are sub-types and neutrophils are part of the same cell family as basophils and eosinophils.


Observational Research - Observational research in any field involves direct observation of phenomena in their natural setting, and systematic gathering of data about what was observed. Three types of observational research are:
  1. Covert observational research: the researchers do not identify themselves;
  2. Overt observational research: the researchers identify themselves as researchers and explain their purpose;
  3. Participant observation: the researcher(s) participate in what they are observing in order to have direct experience of the study phenomena.
Octamer Transcription Factor - A transcription factor which binds to the "ATTTGCAT" sequence.
Odontoblast - One of the cells forming the outer surface of dental pulp that produces the dentin of a tooth. (See FreeDictionary: Odontoblast)
Oligodendrocyte - A cell that supports nerve cells by creating a myelin sheath around axons.
Oligopotent Stem Cells - Oligopotent stem cells can differentiate into a few cell types. Ex., lymphoid or myeloid stem cells. (See Wikipedia: Oligopotency)
Oncogenes - A mutated form of a normal cellular gene. Can lead to the production of a cancer cell. (See Northwestern Biochem glossary: Oncogene).
Oocyte - Developing (immature) egg cell.
Ovarian Hyperstimulation - A complication occasionally seen in women who take certain fertility medicines that stimulate egg production


Parthenogenesis - A form of reproduction in which the ovum develops into a new individual without any fertilization or genetic contribution from a male.
Pharming - A portmanteau of farming and "pharmaceutical" and refers to the use of genetic engineering to insert genes that code for useful pharmaceuticals into host animals or plants that would otherwise not express those genes. As a consequence, the host animals or plants then make the pharmaceutical product in large quantity, which can then be purified and used as a drug product.
Pluripotent Stem Cells - Cells that can differentiate into any other cell type ( i.e., into any of the three germ layers: endoderm (interior stomach lining, gastrointestinal tract, lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous system). However, they cannot be implanted into a uterus to create a fetus. Puripotent stem cells can give rise to any fetal or adult cell type, but alone cannot develop into a fetal or adult animal; they lack the potential to give rise to extraembryonic tissue, specifically the placenta. (See Wikipedia: Pluripotency)
Pluripotent Stem Cells (through iPS) - A stem cell that was made by inducing certain embryonic genes into a donated somatic cell that can differentiate into any other cell type but cannot be implanted into a uterus to create a fetus.
Point Mutation - A type of mutation in which one nucleotide replaces another nucleotide at one point on the DNA sequence.
Polar Body - A small cell (which eventually disintegrates) that is the by-product of meiosis in female animals. One functional ovum and potentially three polar bodies result from meiosis of each primary oocyte. (See Northwestern Biochem glossary: Polar Body)
Poly-arginine anchors - Poly-arginine anchors allow for the channeling of certain proteins into cells; this can lead to generation of iPS cells without genetic alteration of the adult cell.
Polyclonal Antibody - A mixture of immunoglobulin molecules secreted against a specific antigen, each recognizing a different epitope. (See EverythingBio glossary: Polyclonal Antibodies)
Polycomb Group Repressive Complexes - Polycomb-group proteins are a family of proteins first discovered in fruit flies that can remodel chromatin such that epigenetic silencing of genes takes place.
Post Translational Modification - The chemical modification of a protein after its translation.
Pre Embryo - A pre-embryo is a human egg cell that have been fertilized but not yet implanted into a uterus.
Pre-implantation- With regard to an embryo, preimplantation means that the embryo has not yet implanted in the wall of the uterus.
Pre-implantation genetic diagnosis (PGD) - Pre-implantation genetic diagnosis (also known as embryo screening) refers to procedures performed on embryos prior to implantation in the uterus, in order to screen for genetic disease. Embryos found to have certain genetic diseases then would not be implanted. PGD is performed in the context assisted reproductive technology.
Primitive Streak - The embryonic structure that will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation.
Progenitor Cells - Like stem cells, progenitor cells have a tendency to differentiate into a specific type of cell. In contrast to stem cells, however, they are already far more specific: they are pushed to differentiate into their "target" cell. The most important difference between stem cells and progenitor cells is that stem cells can replicate indefinitely, whereas progenitor cells can only divide a limited number of times.
Promoter DNA Methylation - Methylation of GATC sites in the promoter region.
Promoter Region - A region of DNA that facilitates the transcription of a particular gene. Promoters are typically located near the genes they regulate, on the same strand and upstream.
Proteomics - The study of the structure and functions of proteins.
Pronucleus - The nucleus of a sperm or an egg cell during the process of fertilization, after the sperm enters the ovum, but before they fuse
Purine - A nitrogen-containing, double-ring, basic compound that occurs in nucleic acids. The purines in DNA and RNA are adenine and guanine. (See NIH glossary: Purines)
Purkinje Cells - Any of numerous neurons of the cerebral cortex having large flask-shaped cell bodies with massive dendrites and one slender axon.


Regenerative Medicine- The use of biological agents, for example stem cells, to treat diseases and repair damaged or destroyed cell populations or tissues.
Retinal pigment epithelium (RPE) - Retinal pigment epithelium (RPE) is the pigmented cell layer just beyond the neurosensory retina, that nourishes retinal visual cells. Adult retinal stem cells have been found on the margins of the RPE.


Silent Mutation - A point mutation that has no effect at all on the protein being coded for. Silent mutations do not significantly affect protein function because they do not dramatically change the three dimensional structure of the protein.
Somatic Cell Hybridization - Somatic fusion or protoplast fusion, involves two distinct species of plants being fused together to form a new hybrid plant with the characteristics of both, a somatic hybrid. Animal somatic cells of different types also can be fused to obtain hybrid cells, which are very scientifically useful, e.g., to study cell division, gene expression and malignant transformations; for viral replication; for gene or chromosome mapping; and for production of monoclonal antibodies (by producing hybridoma - hybrid cells between an immortalized cell and an antibody producing lymphocyte).
Somatic Cell Nuclear Transfer (SCNT) - A technique that combines an enucleated egg and the nucleus of a somatic cell to make an embryo. (See NIH glossary: Oligodendrocyte)
Stem Cell - Primitive self-renewing cells that can develop into functional differentiated cells.
Stochastic Event - A random event, exhibiting non-deterministic behavior.
Syngeneic Transplant - A transplant in which a patient receives stem cells from his or her identical twin.


T cells - T cells (T lymphocytes) are a type of white blood cell central to cell-mediated immunity. They have a unique T cell receptor (TCR) on the cell surface, exist in several subtypes, and are called T cells because they mature in the thymus.
Telomere - A region of repetitive DNA at the end of a chromosome, which protects the end of the chromosome from deterioration.
Teratocarcinoma - A gonadal tumor.
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 (See NIH glossary: Terratoma) In medical context, grows in reproductive tract as benign tumor of ovary, testis (?); tumor can contains random clusters of mixed cell types (e.g., teeth, hair, organ tissue etc.).
Tissue Plasminogen Activator - A protein involved in the breakdown of blood clots.
Totipotent Stem Cells- Cells that can differentiate into any specialized cell and have the potential to develop into a complete fetus and a placenta.
Transcription factors - These protein complexes help RNA polymerase bind to DNA. By controlling RNA polymerase's access to the gene, transcription factors control the rate at which a gene is transcribed.
Transcriptional Start Site - The location on the DNA, usually after the promoter, where transcription into mRNA begins.
Trans-differentiation - The process in which a non-stem cell differentiates into another type of specialized cell.
Transfection - Infection of a bacterium or cell with DNA or RNA isolated from a bacteriophage or from an animal or a plant virus, resulting in replication of the complete virus.
Translocation - Translocation is a type of chromosomal abnormality in which a chromosome breaks and a portion of it reattaches to a different chromosome. Chromosomal translocations can be detected by analyzing karyotypes of the affected cells. (See NIH glossary: Translocation)


Unipotent Cells - A unipotent cell technically is a progenitor or precursor cell, not a stem cell. Its self renewal in vivo and in vitro is limited. Like oligopotent cells it has only the capacity to develop/differentiate into only one type of tissue/cell type. Ex. Adult skin cells and liver cells (the liver's ability to regenerate from as little as 25% of its original mass is attributed to this property). (See Wikipedia: Unipotency)


Zona Pellucida - A glycoprotein membrane surrounding the plasma membrane of an oocyte.
Zygote - The resulting formation when an ovum is fertilized by a sperm.

Additional Glossary Resources