Hematopoietic potential of neural stem cells: plasticity versus heterogeneity.
Organ-specific stem cells have been identified in a variety of mammalian tissues. These cells hold great promise for cellular therapy if they can reliably produce functional progeny of specific lineages. A central dogma in development has been that organ-specific stem cells are restricted to making the differentiated cell types of the tissue from which they are isolated. However, a substantial body of evidence exists that stem-cell populations from neural and hematopoietic tissues can generate the other cell types, suggesting that adult organ-specific stem cells may have a broader differentiation potential than originally thought. It remains unclear whether this apparent stem cell plasticity is attributable to transdifferentiation of tissue specific stem cells, the co-existence of multiple stem cells with different potentials, or resident totipotent stem cells in these tissues. Recent evidence, in fact, indicates that there may be a fourth explanation for the "apparent" plasticity of stem cells: cell fusion. Here, the authors critically examine the existing data to assess the extent of phenotypic conversion of bone marrow-to-brain and brain-to-blood and discuss some of the contentious issues surrounding these studies. We conclude that there is strong evidence for a multipotent neurohematopoietic stem-cell population in human and mouse brain, although further characterization of these cells will be required if the goal of engineering tissues for therapeutic applications is to be realized.
Shih
Chu-chih
CC
Division of Hematology/Bone Marrow Transplantation, City of Hope National Medical Center, Beckman Research Institute at City of Hope, Duarte, CA 91010, USA. cshih@coh.org
DiGiusto
David
D
Mamelak
Adam
A
Lebon
Thomas
T
Forman
Stephen J
SJ
D000818:Animals; D001773:Blood Cells / Q000166:cytology*; D002454:Cell Differentiation; D002465:Cell Movement / Q000502:physiology; D006801:Humans; D039902:Multipotent Stem Cells / Q000166:cytology; D009474:Neurons / Q000166:cytology*; D033581:Stem Cell Transplantation; D013234:Stem Cells / Q000166:cytology*