More MS news articles for Jan 2002

Stem Cell Glossary

December 18, 2001

The debate over whether the government should finance research on embryonic stem cells has forced politicians and the public to grapple with the arcane language of cell biology. Here are some terms, as gleaned from reports by the National Institutes of Health and other sources.

Repairing the body by harnessing its own repair mechanisms stem cells and signaling proteins to renew damaged tissues and organs.

Master cells that can reproduce indefinitely to form the specialized cells of tissues and organs.

Derived from the inner cell mass of a blastocyst, a 4- to 5-day- old embryo, these cells are thought to be pluripotent meaning they can grow into any of the body's 260 or so cell types. Unlike the egg cell which is totipotent, able to form a complete embryo, the embryonic stem cells do not seem able to form a new blastocyst and cannot by themselves create a new individual.

Embryonic cells that are set aside and protected from maturing. They migrate through the fetus to the ovary or testes, where they form the egg and sperm cells. If removed from the fetus and grown in culture, they behave much like embryonic stem cells.

Stem cells that dwell in the adult body and are far less versatile than embryonic stem cells. Each type generates replacement cells for the particular tissue in which it is found. Scientists are trying to see if adult stem cells can be reprogrammed to produce cells beyond their normal range.

A hollow sphere of some 250 cells that develop four to five days after an egg is fertilized. Inside is a clump of about 30 cells, the inner cell mass, from which the embryo develops. When removed and grown in a laboratory dish, cells from the inner cell mass are called embryonic stem cells. They can be changed while being cultured.

The process in which a stem cell generates a cell with a specialized function. The process begins when certain genes are activated and others silenced, causing the bland, shapeless stem cell to change into some other type of cell.

Creating a genetically identical organism, through any of several techniques. Dolly the sheep, the first mammal to be cloned, was created by inserting DNA from the nucleus of a sheep mammary gland cell into an egg cell emptied of its own nuclear DNA.

The new idea of repairing patients with their own cells, making a skin cell, say, turn into heart cells to repair the heart. This would be accomplished by inserting the nucleus of a patient's skin cell into a donated human egg cell without its own nucleus. The egg cell would reprogram the skin cell nucleus back into its totipotent state. After the egg had become a 5-day-old embryo, embryonic stem cells would be cultured and changed into heart cells for injection into the patient.

Reproduction in which the egg develops into an embryo without fertilization. Parthenogenesis does not occur in mammals, but scientists can use chemicals or electricity to stimulate the eggs of certain animals into dividing as if they had been fertilized. One company has started experiments with human eggs.

Copyright 2001 The New York Times Company