Still other types of cells are incapable of regeneration.
But he said it was unclear how many other types of cells could be created this way.
But contentions that the cells can also form other types of cells, like nerve cells, are more controversial.
Stem cells are undifferentiated cells that have the capacity to renew and develop into other types of cells.
The hope is that the cells might be turned into heart cells, brain cells or other types of cells to repair damaged and diseased organs.
But this growth in volume, Dr. Herbert said, could also represent an increase in nerve fibers, the migration of other types of cells or some type of inflammation.
Similar techniques using other types of cells from patients have been used to fashion bladders and also to grow skin for grafting.
Since these cells can turn into all other types of cells, scientists can study which genes are turned on and off as these transformations occur.
They are now taking cells, like nerve cells, and turning them into other types of cells, like muscle cells.
These cells can be coaxed into differentiating into many other types of cells by the application of appropriate growth factors.
Dr. Lindquist believes the neurons have to last a lifetime, not being renewable like most other types of cells in the body, and that dopamine is easily converted into chemicals that damage the cell's proteins.
