Plasticity of marrow-derived stem cells.

Many exciting discoveries reported over the past 3 years have caused us to expand the paradigm for understanding somatic stem cell plasticity. Within adult organs, there are not only specific stem cells that are capable of producing functional cells of one organ system, but also cells with the flexibility to differentiate into multiple other cell types. In the bone marrow, for example, in addition to hematopoietic stem cells and supportive stromal cells, there are cells with the potential to differentiate into mature cells of the heart, liver, kidney, lungs, GI tract, skin, bone, muscle, cartilage, fat, endothelium and brain. A subpopulation of cells in the brain can differentiate into all of the major cell types in the brain and also into hematopoietic and skeletal muscle cells. In this brief overview, several of these recent findings are summarized.