Glossary
Adult stem cell: A cell present in adults that can generate a limited range of cell types as well as renew itself.
Blastocyst: A developing ball of 50-150 cells that can give rise to an embryo if implanted in a human. A blastocyst is included in the definition of 'embryo' under the HFE Bill.
Cancer stem cell: A proliferating cell thought to be responsible for the generation of new tumour cells.
Cord blood stem cell: A type of pluripotent stem cell found in umbilical cord. Can be stored ('banked').
Cytoplasmic hybrid embryo: A type of human admixed embryo created when human DNA is placed into an animal egg from which the nucleus has been removed, using a process of somatic cell nuclear transfer.
Differentiated cell: A cell that has taken on its final form and function and generally cannot divide further.
Embryo: In developmental biology terms, an embryo is a ball of cells that has matured to the stage where it begins to develop a nervous system, approximately 14 days following fertilisation. Under the HFE Bill, the term 'embryo' also includes blastocysts and eggs that are in the process of fertilisation or undergoing any other process capable of resulting in an embryo.
Embryonic stem cell: A stem cell extracted from an early embryo (a blastocyst) that can be grown in culture and can give rise to all the different cell types of a body (i.e. is pluripotent).
Haematopoietic stem cells: Blood-forming stem cells found in bone marrow.
HFEA: Human Fertilisation and Embryology Authority.
HFE Bill: Human Fertilisation and Embryology Bill.
Human admixed embryo: A ball of cells containing human and animal material, which will not be allowed to develop beyond blastocyst stage. These are specifically excluded from the definition of an embryo in the new HFE Bill.
Induced pluripotent stem cell: A differentiated cell that has been modified so that it regains its ability to develop into other types of cell.
Mesenchymal stem cells: Developmentally flexible adult stem cells found in the bone marrow and other tissues, including fat tissue, that are relatively easy to extract and grow in culture. Can form a range of cell types, but not blood cells.
Mitochondrial DNA: Genetic material in mitochondria, the structures in cells that are important for metabolism and energy production (the cell's 'battery'). This DNA does not give rise to any special human or animal characteristics.
Neural stem cells: Adult stem cells able to differentiate into a range of cells found in the nervous system.
Pluripotent stem cell: A stem cell able to produce all the different cell types of an organism, but not develop into a complete organism.
Reproductive cloning: Cloning of a new adult using somatic cell nuclear transfer techniques.
Somatic cell nuclear transfer (SCNT): The process by which the nuclear genetic material is removed from an adult cell, e.g. a skin cell, and transferred into an egg cell from which the nucleus has been removed.
Stem cell: A stem cell able to produce a range of differentiated cell types while also renewing itself.
Therapeutic cloning: The transfer of a nucleus (e.g. from an adult cell) to an egg that has had its nucleus removed; the egg is stimulated to develop to blastocyst stage, when embryonic stem cells can be isolated. Also called ‘somatic cell nuclear transfer’. The technique is used to create embryonic stem cells that are genetically identical to the donor.
Totipotent stem cell: A stem cell able to develop into a complete organism.
Image: Human embryonic stem cells; Annie Cavanagh, Wellcome Images
