RUNX2 and Miyoshi myopathy: To further investigate the role of soluble factors or cell–cell contacts in the modulation of RUNX2 expression, we compared basal RUNX2 expression in MSC and MM cells in different experimental conditions: (1) alone: MM cells grown without a MSC feeder layer and MSCs grown without MM cells; (2) co-culture: MM cells grown on a feeder layer of MSCs, in which the cross-talk was mediated both by soluble factors and by cell–cell interactions; (3) transwell co-culture: MM cells and MSCs grown in co-culture but physically separated so that cross-talk was mediated only by soluble factors.