Stem Cell/Cloning Definitions and Terms



Cell Types:
          Adult Stem Cells: Undifferentiated cells throughout the body that divide to replenish dying cells and regenerate damaged tissues (i.e. hematopeietic cells of the bone marrow).
          Cord Blood Stem Cells: Stem cells derived from the blood of the placenta and umbilical cord after birth.
          Embryonic Stem Cell: Cells cultured from the undifferentiated inner cell mass of an early stage embryo (blastocyst of a human embryo-between 50 and 150 cells big)-this destroys (kills) the human embryo.
          Induced Pluropotent Stem Cells (IPCS): Inducing adult somatic cells to behave as Embryonic Stem Cells.
          Somatic Cell: Fully differentiated non-stem cells that do not have self-renewal tendencies.
          Stem Cell-General: Primal undifferentiated cells that retain the ability to divide and differentiate into other cell types.

Chimera: An animal with features of at least 2 different species, such as a horse with a goats head! Mice with human brain cells implanted; it has been attempted!

Cloning Definitions:
          Cloning-General: Creating a new organism or group of cells with the same genetic information as an existing cell. It is an asexual method of reproduction because fertilization with another gamete does not take place. A nucleus is removed from the receiving egg (oocyte) and the nucleus of a donor somatic cell is injected into it. If the donor nucleus is from the same maternal line the mitochondrial genome is also transferred; if not, it is not also transferred (cross-species mitochondrial genome transfer can result in incompatibilities or inviability-death).
          Therapuetic Cloning: Process involving somatic cell nuclear transfer (SCNT) or altered nuclear transfer (ANT) which uses an egg (oocyte) of which the nucleus has been removed and replaces it with the nucleus from another donor cell. In humans this creates an embryo from which stem cells can be harvested-the embryo killed in the process. Scientists are trying to argue that by using the technique of altered nuclear transfer (ANT-see below) there is not really an embryo developed (the nucleus or the genetic material is altered to not allow the cells (an embryo!) to develop past a certain point).
          Reproductive Cloning: Implanting the created human clone (made from taking an egg (oocyte) from which the nucleus has been removed and replacing it with the nucleus from another donor cell-SCNT) into a uterus and taking it to term or birth.

Nuclear Transfer: Transferring the nucleus from one cell to another one; exchanging it for that cell's nucleus.
          Altered Nuclear Transfer (ANT): The nucleus of a somatic cell is removed and inserted into an egg cell in which the nucleus has been removed and discarded. The difference in ANT from SCNT is that the nucleus or cytoplasm of the egg is supposedly ‘altered’ to make a stem cell that lacks embryo potential (no embryogenesis-no embryo development).
          Altered Nuclear Transfer/Oocyte Assited Reprogramming (Ant-Oar): The Nucleus of a somatic cell is removed and inserted into an egg cell in which the nucleus has been removed and discarded. The difference in Ant and Ant-Oar is that instead of knocking out a gene for development, genes are "jump-started" to skip the Totipotent embryo stage and move directly to the Pluripotent stem cell stage. Supposedly never becoming an embryo at all but leaving embryonic stem cells to use.
          Somatic Cell Nuclear Transfer (SCNT): The nucleus of a somatic cell is removed and inserted into an egg cell in which the nucleus has been removed and discarded.

Parthenogenesis: A process by which an embryo is created solely from a female oocyte without genetic input from a male. An egg is either ‘kept’ from donating half of its 46 chromosomes to connect with a halved male cell (23 chromosomes) or is stimulated to replicate its halved 23 chromosomes to result in a full 46 chromosomes. In either case, the embryo’s full compliment of 46 chromosomes comes solely from the female.

Plasticity: The 'flexibility' or ease of the ability to differentiate cells

Potency: Specifies the differentiation potential of the stem cell (the potential to differentiate into different cell types):
          Multipotent: Precursors of fully differentiated somatic (single type of tissue cells); produce only cells of a closely related family of cells (i.e. hematopoeietic stem cells that differentiate into red blood cells, white blood cells platelets, etc.).
          Pluripotent: Stem cells that are descendants of totipotent cells and can differentiate into cells derived from the 3 germ layers (cells that give rise to organs and tissues).
          Totipotent: Stem cells that are capable of developing into the entire organism (can differentiate into embryonic and extra-embryonic cell types). These are ‘master’ stem cells that contain the ‘blueprint’ of development of the whole organism.
          Unipotent: Cells that can produce only one cells type, but have the property of self-renewal which distinguishes them from non-stem cells.

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