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Appendix B Glossary Adult stem cellâAn undifferentiated cell found in a differentiated tissue that can renew itself and (with limitations) differentiate to yield the specialized cell types of the tissue from which it originated. AndrogenesisâDevelopment in which the embryo contains only paternal chromosomes. Autologous transplantâTransplanted tissue derived from the intended re- cipient of the transplant. Such a transplant helps to avoid complications of immune rejection. BlastocoelâThe cavity in the center of a blastocyst. BlastocystâA preimplantation embryo of 50â250 cells depending on age. The blastocyst consists of 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). BlastomereâA single cell from a morula or early blastocyst, before the dif- ferentiation into trophectoderm and inner cell mass. Bone marrowâThe soft, living tissue that fills most bone cavities and con- tains hematopoietic stem cells, from which all red and white blood cells evolve. The bone marrow also contains mesenchymal stem cells from which a number of cell types arise, including chondrocytes, which produce cartilage, and fibroblasts, which produce connective tissue. N â â ew or modified wording is indicated by underlining, deleted text by strikeout. 39
40 Appendix B ChimeraâAn organism composed of cells derived from at least two ge- netically different cell types. The cells could be from the same or separate species. DifferentiationâThe process whereby an unspecialized early embryonic cell acquires the features of a specialized cell, such as a heart, liver, or muscle cell. DNAâDeoxyribonucleic acid, a chemical found primarily in the nucleus of cells. DNA carries the instructions for making all the structures and materi- als the body needs to function. EctodermâThe outermost of the three primitive germ layers of the embryo; it gives rise to skin, nerves, and brain. Egg cylinderâAn asymmetric embryonic structure that helps to determine the body plan of the mouse. ElectroporationâMethod of introducing DNA into a cell. EmbryoâAn animal in the early stages of growth and differentiation that are characterized by cleavage, laying down of fundamental tissues, and the formation of primitive organs and organ systems; especially the developing human individual from the time of implantation to the end of the eighth week after conception, after which stage it becomes known as a fetus. Embryoid bodies (EBs)âClumps of cellular structures that arise when em- bryonic stem cells are cultured. Embryoid bodies contain tissue from all three germ layers: endoderm, mesoderm, and ectoderm. Embryoid bodies are not part of normal development and occur only in vitro. Embryonic diskâA group of cells derived from the inner cell mass of the blastocyst, which later develops into an embryo. The disk consists of three germ layers known as the endoderm, mesoderm, and ectoderm. Embryonic germ (EG) cellsâCells found in a specific part of the embryo or fetus called the gonadal ridge that normally develop into mature gametes. The germ cells differentiate into the gametes (oocytes or sperm). http://www.nlm.nih.gov/medlineplus/mplusdictionary.html. In common parlance, âem- bryoâ is used more loosely and variably to refer to all stages of development from fertilization until some ill-defined stage when it is called a fetus. There are strictly defined scientific terms such as âzygote,â âmorula,â and âblastocystâ that refer to specific stages of preimplantation development (see Chapter 2 of NRC and IOM, 2005). In this report, we have used the more precise scientific terms where relevant but have used the term âembryoâ where more precision seemed likely to confuse rather than clarify.
Appendix B 41 Embryonic stem (ES) cellsâPrimitive (undifferentiated) cells derived from the early embryo that have the potential to become a wide variety of special- ized cell types. EndodermâInnermost of the three primitive germ layers of the embryo; it later gives rise to the lungs, liver, and digestive organs. Enucleated cellâA cell whose nucleus has been removed. EpidermisâThe outer cell layers of the skin. EpigeneticâRefers to modifications in gene expression that are controlled by heritable but potentially reversible changes in DNA methylation or chro- matin structure without involving alteration of the DNA sequence. EpitheliumâLayers of cells in various organs, such as the epidermis of the skin or the lining of the gut. These cells serve the general functions of protection, absorption, and secretion, and play a specialized role in moving substances through tissue layers. Their ability to regenerate is excellent; the cells of an epithelium may replace themselves as frequently as every 24 hours from the pools of specialized stem cells. Feeder cell layerâCells that are used in culture to maintain pluripotent stem cells. Feeder cells usually consist of mouse embryonic fibroblasts. FertilizationâThe process whereby male and female gametes unite to form a zygote (fertilized egg). FibroblastsâCells from many organs that give rise to connective tissue. GameteâA mature male or female germ cell, that is, sperm or oocyte, respectively. GastrulationâThe procedure by which an animal embryo at an early stage of development produces the three primary germ layers: ectoderm, mesoderm, and endoderm. GeneâA functional unit of heredity that is a segment of DNA located in a specific site on a chromosome. A gene usually directs the formation of an enzyme or other protein. Gene targetingâA procedure used to produce a mutation in a specific gene. Genital ridgeâAnatomic site in the early fetus where primordial germ cells are formed. GenomeâThe complete genetic material of an organism.
42 Appendix B GenotypeâGenetic constitution of an individual. Germ cellâA sperm or egg or a cell that can become a sperm or egg. All other body cells are called somatic cells. Germ layerâIn early development, the embryo differentiates into three dis- tinct germ layers (ectoderm, endoderm, and mesoderm), each of which gives rise to different parts of the developing organism. Germ lineâThe cell lineage from which the oocyte and sperm are derived. Gonadal ridgeâAnatomic site in the early fetus where primordial germ cells (PGCs) are formed. GonadsâThe sex glandsâtestis and ovary. HematopoieticâBlood-forming. Hematopoietic stem cell (HSC)âA stem cell from which all red and white blood cells evolve and that may be isolated from bone marrow or umbilical cord blood for use in transplants. HepatocyteâLiver cell. HeterologousâFrom genetically different individuals. hES cellâHuman embryonic stem cell; a type of pluripotent stem cell. Histocompatibility antigensâGlycoproteins on the surface membranes of cells that enable the bodyâs immune system to recognize a cell as native or foreign and that are determined by the major histocompatibility complex. Homologous recombinationâRecombining of two like DNA molecules, a process by which gene targeting produces a mutation in a specific gene. hPS cellsâHuman pluripotent stem cells derived from non-embryonic sources. HybridâAn organism that results from a cross between gametes of two different genotypes. Immune system cellsâWhite blood cells, or leukocytes, that originate in the bone marrow. They include antigen-presenting cells, such as dendritic cells, T and B lymphocytes, macrophages, and neutrophils, among many others. Immunodeficient miceâGenetically altered mice used in transplantation experiments because they usually do not reject transplanted tissue. ImmunogenicâRelated to or producing an immune response.
Appendix B 43 ImmunosuppressiveâSuppressing a natural immune response. ImplantationâThe process in which a blastocyst implants into the uterine wall, where a placenta forms to nurture the growing fetus. Inner cell massâThe cluster of cells inside the blastocyst that give rise to the embryonic disk of the later embryo and, ultimately, the fetus. InterspecificâBetween species. In uteroâIn the uterus. In vitroâLiterally, âin glass,â in a laboratory dish or test tube; in an artificial environment. In vitro fertilization (IVF)âAn assisted reproductive technique in which fertilization is accomplished outside the body. In vivoâIn the living subject; in a natural environment. KaryotypeâThe full set of chromosomes of a cell arranged with respect to size, shape, and number. Leukemia inhibitory factor (LIF)âA growth factor necessary for maintaining mouse embryonic stem cells in a proliferative, undifferentiated state. Mesenchymal stem cellsâStem cells found in bone marrow and elsewhere from which a number of cell types can arise, including chondrocytes, which produce cartilage, and fibroblasts, which produce connective tissue. MesodermâThe middle layer of the embryonic disk, which consists of a group of cells derived from the inner cell mass of the blastocyst; it is formed at gastrulation and is the precursor to bone, muscle, and connective tissue. MorulaâA solid mass of 16â32 cells that resembles a mulberry and results from the cleavage (cell division without growth) of a zygote (fertilized egg). Mouse embryonic fibroblast (MEF)âCells used as feeder cells in culturing pluripotent stem cells. MultipotentâCapable of differentiation into a limited spectrum of differ- entiated cell types. Neural stem cell (NSC)âA stem cell found in adult neural tissue that can give rise to neurons, astrocytes, and oligodendrocytes. Nuclear transfer (NT)âReplacing the nucleus of one cell with the nucleus of another cell.
44 Appendix B OocyteâDeveloping egg; usually a large and immobile cell. OvariectomyâSurgical removal of an ovary. ParthenogenesisâDevelopment in which the embryo contains only maternal chromosomes. PassageâA round of cell growth and proliferation in culture. PhenotypeâVisible properties of an organism produced by interaction of genotype and environment. PlacentaâThe oval or discoid spongy structure in the uterus from which the fetus derives its nourishment and oxygen. Pluripotent cellâA cell that has the capability of developing into cells of all germ layers (endoderm, ectoderm, and mesoderm). Precursor cellsâIn fetal or adult tissues, partly differentiated cells that divide and give rise to differentiated cells. Also known as progenitor cells. Preimplantation genetic diagnosis (PGD)âA procedure applied to IVF em- bryos to determine which ones carry deleterious mutations predisposing to hereditary diseases. Primary germ layersâThe three initial embryonic germ layersâendo- derm, mesoderm, and ectodermâfrom which all other somatic tissue types develop. Primordial germ cellâA cell appearing during early development that is a precursor to a germ cell. Primitive streakâThe initial band of cells from which the embryo begins to develop. The primitive streak establishes and reveals the embryoâs head-tail and left-right orientations. PseudopregnantâRefers to a female primed with hormones to accept a blastocyst for implantation. Somatic cellâAny cell of a plant or animal other than a germ cell or germ cell precursor. Somatic cell nuclear transfer (SCNT)âThe transfer of a cell nucleus from a somatic cell into an egg (oocyte) whose nucleus has been removed. Stem cellâA cell that has the ability to divide for indefinite periods in vivo or in culture and to give rise to specialized cells.
Appendix B 45 TeratomaâA tumor composed of tissues from the three embryonic germ layers. Usually found in ovary or testis. Produced experimentally in animals by injecting pluripotent stem cells to determine the stem cellsâ abilities to differentiate into various types of tissues. Tissue cultureâGrowth of tissue in vitro on an artificial medium for experi- mental research. TransfectionâA method by which experimental DNA may be put into a cultured cell. TransgeneâA gene that has been incorporated into a cell or organism and passed on to successive generations. TransplantationâRemoval of tissue from one part of the body or from one individual and its implantation or insertion into another, especially by surgery. TrophectodermâThe outer layer of the developing blastocyst that will ulti- mately form the embryonic side of the placenta. TrophoblastâThe extraembryonic tissue responsible for negotiating implan- tation, developing into the placenta, and controlling the exchange of oxygen and metabolites between mother and embryo. UndifferentiatedâNot having changed to become a specialized cell type. Xenograft or xenotransplantâA graft or transplant of cells, tissues, or organs taken from a donor of one species and grafted into a recipient of another species. ZygoteâA cell formed by the union of male and female germ cells (sperm and egg, respectively).