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more than neural cells and muscle cells, respectively. The 
implications of this will be discussed below. Studies are ongoing to 
determine if cultivation of MAPC from other organs is possible, and 
whether culture of MAPC, like ES cells, is mouse-strain dependent. 
Initial studies suggest that a population of MAPC-like cells can also 
be cultured from bone marrow from cynomologous monkeys 
(unpublished observations)(studies done by our collaborator Felipe 
Prosper, University of Navarra, Pamplona, Spain) and from bone 
marrow of dogs (unpublished observations) (studies done at the 
University of Minnesota). 
Non-senescent nature of MAPC: 
Unlike most adult somatic stem cells, MAPC proliferate 
without obvious signs of senescence, and have active telomerase. In 
humans, the length of MAPC telomeres is 3-5kB longer than in 
neutrophils and lymphocytes, and telomere length is not different 
when MAPC are derived from young or old donors \ This suggests 
that MAPC are derived from a population of cells that either has 
active telomerase in vivo, or that is highly quiescent in vivo, and 
therefore has not yet incurred telomere shortening in vivo. In human 
MAPC cultures we have not yet seen cytogenetic abnormalities. As 
human MAPC are however undergoing symmetrical cell divisions, it 
remains possible that despite lack of gross cytogentic changes, 
minor mutations accumulate over time. We are therefore planning to 
use comparative genomic hybridization to address the question at 
what time genetic abnormalities occur, if they do. Initial results from 
gene array analysis suggest that MAPC, like ES cells, have a large 
number of DNA repair genes expressed (unpublished observations), 
which may protect them from more frequent genetic abnormalities in 
view of the fact that they undergo multiple sequential symmetrical 
cell divisions. 
However, several subpopulations of mouse MAPC, and to a 
lesser extent rat MAPC, have become aneuploid, even though 
additional subpopulations thawed subsequently were 
cytogenetically normal. Aneuploidy is seen more frequently once 
mouse (and rat) MAPC have been expanded for >60-70 population 
doublings and following repeated cryopreservtions and thawing 
episodes. This characteristic of mouse MAPC is not dissimilar from 
other mouse cell populations, including mouse ES cells. 
Stringent culture conditions required for maintenance of the 
undifferentiated state of MAPC: 
PRE -PUBLICATION VERSION 
