FACTBOX: Embryonic stem cells, the ultimate master cell

(Reuters) - The U.S. government approved the first 13 new batches of human embryonic stem cells on Wednesday, opening their use for federally funded research under reduced restrictions announced by President Barack Obama in March.

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 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 diabetes.

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

* President George W. Bush restricted the use of federal funds to only a few batches of already-existing human embryonic stem cells in 2001. President Barack Obama lifted the restriction in March and asked the National Institutes of Health to decide which embryonic stem cells could be used in federally funded research.

* States such as California, New York, Connecticut, Maryland, Illinois, Massachusetts and New Jersey acted on their own to fund this research during the years of the Bush restrictions. Institutions such as Harvard University also set up separate operations to pursue the research using private money.

* Several companies are pursuing stem cell research including Geron Corp, Stemcells Inc, Advanced Cell Technology, NeuralStem, Aastrom Biosciences Inc, Reneuron Group Plc, Osiris Therapeutics Inc, Neostem Inc, Cytori Therapeutics Inc, iZumi Bio Inc and International Stem Cell Corp.

* U.S. legislation called the Dickey Amendment forbids the use of federal funds for the creation or destruction of human embryos for research, but new U.S. policy allows federally funded researchers to work with cells someone else took from an embryo.

* Researchers have discovered how to make embryonic-like cells from ordinary cells, called induced pluripotent stem cells. Opponents of embryonic stem cell research say research can focus on this field, but most experts in the field agree that all approaches must be pursued.

(Reporting by Maggie Fox in Washington; Editing by Cynthia Osterman)