Genetic and ultrastructural demonstration of strong reversibility in human mesenchymal stem cell. 
We examined human bone marrow mesenchymal stem cells by applying real-time quantitative polymerase chain reaction (PCR) (RT-PCR) technology and electron-microscopic techniques.  Our RT-PCR demonstrated that the values of peroxisome proliferation-activated receptor gamma2 (PPARgamma2) and lipoprotein lipase (LPL) mRNA dramatically increased according to adipogenic stimulation.  The expressions of both PPARgamma2 and LPL mRNA were significantly reduced ( P<0.01) and almost disappeared after stimulation had ceased.  The expressions of both genes, however, increased again by stimulation even though the cells were in a dedifferentiated state for a month.  In the ultrastructural study, over 80% of the cells proceeded into morphologically well-developed adipocytes at the 12th day of induction/maintenance which were packed with lipid droplets and clusters.  In the next process these lipid products were excreted from the cell bodies and the peripheral small parts containing numerous droplets were torn from the greater parts, which stuck tightly to each other and adhered to culture dishes.  Adipocytes were not detected in the culture media during the final stage.  The total cell number was equal to and over 90% of the cells dedifferentiated into fibroblast-like stem cells during the final maintenance period of 1 month.  Furthermore the dedifferentiated cells quickly differentiated again into adipocytes by stimulation even if they were quiescent for 1 month.  Thus we conclude that mesenchymal stem cells have strong reversibility from both the genetic and morphological points of view.