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2008 ; 4
(3
): 137-47
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The paradoxical dynamism of marrow stem cells: considerations of stem cells,
niches, and microvesicles
#MMPMID18665337
Quesenberry PJ
; Aliotta JM
Stem Cell Rev
2008[Sep]; 4
(3
): 137-47
PMID18665337
show ga
Marrow stem cell regulation represents a complex and flexible system. It has been
assumed that the system was intrinsically hierarchical in nature, but recent data
has indicated that at the progenitor/stem cell level the system may represent a
continuum with reversible alterations in phenotype occurring as the stem cells
transit cell cycle. Short and long-term engraftment, in vivo and in vitro
differentiation, gene expression, and progenitor numbers have all been found to
vary reversibly with cell cycle. In essence, the stem cells appear to show
variable potential, probably based on transcription factor access, as they
proceed through cell cycle. Another critical component of the stem cell
regulation is the microenvironment, so-called niches. We propose that there are
not just several unique niche cells, but a wide variety of niche cells which
continually change phenotype to appropriately interact with the continuum of stem
cell phenotypes. A third component of the regulatory system is microvesicle
transfer of genetic information between cells. We have shown that marrow cells
can express the genetic phenotype of pulmonary epithelial cells after
microvesicle transfer from lung to marrow cells. Similar transfers of tissue
specific mRNA occur between liver, brain, and heart to marrow cells. Thus, there
would appear to be a continuous genetic modulation of cells through microvesicle
transfer between cells. We propose that there is an interactive triangulated Venn
diagram with continuously changing stem cells interacting with continuously
changing areas of influence, both being modulated by transfer of genetic
information by microvesicles.