<P> Adult stem cells remain in an undifferentiated state throughout adult life . However, when they are cultured in vitro, they often undergo an' aging' process in which their morphology is changed and their proliferative capacity is decreased . It is believed that correct culturing conditions of adult stem cells needs to be improved so that adult stem cells can maintain their stemness over time . </P> <P> A Nature Insight review defines niche as follows: </P> <P> "Stem - cell populations are established in' niches'--specific anatomic locations that regulate how they participate in tissue generation, maintenance and repair . The niche saves stem cells from depletion, while protecting the host from over-exuberant stem - cell proliferation . It constitutes a basic unit of tissue physiology, integrating signals that mediate the balanced response of stem cells to the needs of organisms . Yet the niche may also induce pathologies by imposing aberrant function on stem cells or other targets . The interplay between stem cells and their niche creates the dynamic system necessary for sustaining tissues, and for the ultimate design of stem - cell therapeutics...The simple location of stem cells is not sufficient to define a niche . The niche must have both anatomic and functional dimensions .") </P> <P> Though the concept of stem cell niche was prevailing in vertebrates, the first characterization of stem cell niche in vivo was worked out in Drosophila germinal development . </P>

Where is the blood stem cell niche located in the body and what is it called