FACTBOX: Embryonic stem cells, the ultimate master cell

(Reuters) - The U.S. National Institutes of Health released final rules on Monday governing federal funding of human embryonic stem cell research.

Following are some facts about stem cells:

* Stem cells are the body's master cells, the source of all cells and tissue, including brain, blood, heart, bones and muscles.

* Embryonic stem cells come from days-old embryos and can produce any type of cell in the body.

* Scientists generally harvest embryonic stem cells from embryos left over after in vitro fertilization attempts at fertility clinics. They can also be produced using cloning technology but the new U.S. rules allow for federal funding only of work on surplus IVF embryos.

* Scientists hope to harness the transformational qualities of stem cells to treat a variety of diseases, including injuries, cancer and cystic fibrosis.

* The issue is controversial because some people believe the destruction of any human embryo is wrong.

* Several companies are pursuing stem cell research including Geron Corp. which last week teamed up with General Electric Co to use stem cells to test new drugs for toxicity.

* Other companies involved in stem cell research include Stemcells Inc., Advanced Cell Technology, NeuralStem, Aastrom Biosciences Inc., Reneuron Group Plc., Thermogenesis, Osiris Therapeutics Inc, Neostem Inc., Cytori Therapeutics Inc., iZumi Bio Inc., and International Stem Cell Corporation.