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A newly discovered stem cell that keeps bones growing
Bone elongation requires the maintenance of a growth plate of cartilage. Two studies have now identified stem cells specific to this structure that give rise to both cartilage cells and bone-marrow stem cells.
The growth of long bones in young mammals (including children) is driven by the growth plate, a zone of cartilage that separates each end of the bone from the main shaft. The growth plate contains three distinct types of cartilage cell (chondrocyte). Round chondrocytes in the resting zone of the growth plate differentiate into flat, proliferating chondrocytes that form columns along the bone’s longitudinal axis. These cells later become hypertrophic chondrocytes that cease to proliferate and are replaced by bone and bone marrow. Consequently, growth-plate chondrocytes need to be replenished continuously and the stem cells that fuel this process have long been sought. Writing in Nature, Newton et al.1 and, previously, Mizuhashi et al.2 have identified a type of skeletal stem cell in the resting zone of mouse bones that gives rise to all types of growth-plate chondrocyte, as well as some of the long-lived stem cells of the bone-marrow stroma (non-blood-lineage cells).