Stem cell plasticity: Recapping the decade, mapping the future Neil D. Theise  Experimental Hematology  Volume 38, Issue 7, Pages 529-539 (July 2010) DOI: 10.1016/j.exphem.2010.04.013 Copyright © 2010 ISEH - Society for Hematology and Stem Cells Terms and Conditions

Figure 1 Pathways of cell plasticity. 1: Canonical cell lineage differentiation pathways of both development and adult tissue maintenance and repair. Shifts between one pathway or another respond to the tissue or systemic needs of the organism, either as preprogrammed processes or as a repair/regeneration reaction to injury. 2: Dedifferentiation and redifferentiation may be seen when adult cells return to a blastema-like state in response to injury, then differentiating into differentiated cell populations as part of repair or regeneration. This is most commonly recognized in amphibians, but is also well-documented in fetal mammals (including humans) and in some adult mammals, as well. Such a process may be demonstrable in human neoplasias. 3: The change from one lineage to another in response to cues from the microenvironment is the pathway most often referred to as “plasticity” in the last decade and engendered the most controversy. The degree to which this takes place in living organisms depends on whether there is injury and, if it is present, its nature and severity. Although the physiologic role of this process may still be debated, evidence in adult mammals that it does take place to some degree is well-documented. How to manipulate it for therapeutic and/or industrial purposes is the pressing question. 4: Nuclear reprogramming by cell-to-cell fusion (a), sometimes followed by nuclear fusion (b) is also well-documented. Moreover, postfusion reduction division (c) has also been confirmed. Like the pathway of direct differentiation, the degree to which cell-to-cell fusion, with or without subsequent reduction division, plays significant physiologic roles is not yet clear. Experimental Hematology 2010 38, 529-539DOI: (10.1016/j.exphem.2010.04.013) Copyright © 2010 ISEH - Society for Hematology and Stem Cells Terms and Conditions