Lack of Gfi1 in mouse BMSCs decreases the degree of MM repression of Runx2 in vitro. BMSCs recovered from Gfi1^+/+ and Gfi1^−/− mice were expanded in culture for 3 to 4 weeks. The BMSCs were then exposed to 5TGM1-GFP-TK cells in a transwell for 48 hours followed by either RNA harvest (day 0) or 5-day incubation in OB differentiation media before RNA harvest (day 5). RNAs were analyzed by quantitative PCR for (A) Gfi1 and (B) Runx2 levels. The Runx2 expression in the MM-exposed Gfi1^−/− BMSCs was significantly increased relative to the MM-exposed Gfi1^+/+ BMSCs (P < .05). BMSCs from Gfi1^+/− mice were also analyzed but were found to behave identically to Gfi1^+/+ and were not included for clarity.