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Monitoring Stem Cell Research 
Currently we do not fully understand the mechanism(s) 
underlying the culture selection of MAPC. We have definitive data to 
demonstrate that the pluripotency of MAPC is not due to co-culture 
of several stem cells. 
Pluripotency cannot be attributed to multiple stem cells: 
First, using retroviral meirking studies we have definitive 
proof that a single cell can differentiate in vitro to cells of mesoderm, 
both mesenchymal and non-mesenchymal, neuroectoderm and 
hepatocyte-like cells, and this for human mouse and rat MAPC 
Second, we have shown that a single mouse MAPC is sufficient for 
generation of chimeric animals Indeed, we published that 1/3 
animals born from blastocysts in which a single MAPC was injected 
were chimeric with chimerism degrees varying between 1 and 45%. 
This rules therefore out that the pluripotent nature of these cells is 
due to co-existence in culture of multiple somatic stem cells. 
Cell fusion is not likely explanation: 
A second possibility for the greater degree of differentiation 
potential would be that cells undergo fusion and acquire via this 
mechanism greater pluripotency. Fusion has been shown to be 
responsible for apparent ES characteristics of marrow and neural 
stem cells that had been cocultured with ES cells in vitro, and 
more recently for the apparent lineage switch of bone marrow cells 
to hepatocytes when hematopoietic cells were infused in animals 
with hereditary tyrosinemia due to lack of the fumarylacetoacetate 
hydroxylase (FAH) gene ^^[Wang et al, Nature 2003]. In the former 
two studies, the majority of genes expressed in the marrow or neural 
cell that fused with ES cells were silenced, and the majority of the 
genes expressed in ES cell were persistently expressed. Likewise for 
the bone marrow-hepatocyte fusion, the majority of genes expressed 
normally in hematopoioetic cells (except the FAH gene) were 
silenced whereas genes expressed in hepatocytes predominated. 
Finally, the cells generated were in general tetraploid or aneuploid. 
We do not believe that this phenomenon underlies the 
observation that MAPC are pluripotent. Cultivation and 
differentiation in vitro (in general, except the final differentiation step 
for neuroectoderm) does not require that MAPC are co-cultured with 
other cells, making the likelihood that MAPC are the result of fusion 
very low. Smith et al suggested in a recent commentary that MAPC 
could be caused by fusion of multiple cell types early on during 
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