DIFFERENTIATION POTENTIAL OF CONDITIONALLY IMMORTALIZED MESENCHYMAL PROGENITOR CELLS FROM ADULT MARROW OF A H-2K(B)-TSA58 TRANSGENIC MOUSE

Primary cultures were initiated from marrow, spleen, and bone explants of an adult H-2K(b)-tsA58 transgenic mouse (immortomouse). All cultur es were initiated in immortalizing conditions, and an additional marro w culture was first incubated for 1 week in standard conditions and th en switched to immortalizing conditions. Marrow cells immediately immo rtalized were designated the marrow immediate population (MIP); those immortalized after 1 week were termed the marrow delayed population (M DP). MIP and MDP cells both contained a mixture of fibroblastic or fla ttened cells, and the MIP cells contained an additional subpopulation of adipocytic (Oil Red-O positive) cells. Alkaline phosphatase express ion was induced by dexamethasone (10(-7) M) in MDP cells while MIP, sp leen, and bone explant cells had only a low level of expression. MDP a nd MIP cells differentiated into bone when combined with porous calciu m phosphate ceramics and implanted subcutaneously into nude mice while bone- and spleen-derived cells did not. Clones were isolated from the MDP and MIP cell populations and tested for differentiated phenotypes . Some MIP-derived clones exhibited adipocytic characteristics while M DP-derived subclones were negative. Histologic examination of porous c eramic implanted clones showed that all of the clones had osteogenic p otential. Clones exposed to either dexamethasone, human recombinant bo ne morphogenetic protein-2, or horse serum plus hydrocortisone showed differences in expression of adipocytic or osteogenic markers. These i mmortalized cultures have retained both adipocytic and osteogenic pote ntial even after 1 year of continuous culture, and provide a model sys tem for clonal analysis of the developmental potential of marrow-deriv ed mesenchymal precursor cells. (C) 1996 Wiley-Liss, Inc.