Cell Differentiation No Barrier to Cloning

Dolly the cloned ewe has been at the center of controversy since she was announced to the world in 1997. Beneath the philosophical considerations, the science of the cloning feat--in particular the type of cell used to kick off the process--has been an issue of some debate. Some have argued that so-called adult stem cells--root cells in most tissue that kick into action to replace damaged tissue--must have been involved. But a new test in mice shows that adult stem cells are actually worse than regular cells for the purposes of cloning with current techniques. Moreover, it delivered two cloned pups from the genetic material contained in fully formed white blood cells.

Cloning relies on a process known as somatic cell nuclear transfer, in which the nucleus of a donor cell is transferred into a fertilized egg that has been emptied of its chromosomes. That egg now contains an exact duplicate of the donor's genome, and if all goes well when it is implanted into a surrogate mother, a clone will result. Xianzhong Yang of the University of Connecticut and Tao Cheng of the University of Pittsburgh as well as a host of colleagues examined the cloning potential of three different types of cells: hematopoietic stem cells, progenitor cells and granulocytes. Each represents a different stage in the differentiation process of blood cells; stem cells can become any kind of blood cell, progenitor cells are already on a particular track and granulocytes are a specific type of white blood cell (further specified as neutrophils).