Mineralization of adult mouse bone marrow in vitro

Murine adult bone marrow exhibits mineralizing capacity in vitro as is demonstrated by the new in vitro assay we report here. In less than 2 weeks after the onset of the cultures, mineralization is obtained in more than 80% of the marrow cultures. Moreover, morphological studies reveal that during incubation phenotypic changes related to osteogenic differentiation occur at the extracellular matrix as well within cell populations. Well banded collagen is synthesized. Matrix vesicles and needles of hydroxy-apatite crystals are observed via transmission electron microscopy. Osteoblast-like cells are present with membrane-associated alkaline phosphatase activity. The mineralization is specific for cultured bone marrow and is not observed in cultured spleen fragments as is shown via 85Sr uptake, calcein uptake and histomorphology. No inducing agent is added to the tissue culture medium except for 10% fetal calf serum, beta-glycerophosphate (10(-2) M) and ascorbic acid. However, the prerequisite for obtaining mineralization is the three-dimensional structure of the marrow in culture. The in vitro organ culture we developed may provide the opportunity to identify which marrow cells have osteogenic potential and to investigate the mechanisms triggering differentiation towards osteogenesis.