Lineage potential of adult human MSCs. MSCs are characterized by their multilineage differentiation potentials, including bone, cartilage, adipose tissue, muscle, tendon, and stroma. This figure depicts some of the in vitro culture conditions (boxed) that promote the respective differentation process into a specific lineage. Signaling pathways and/or components or events shown to be involved in lineage-specific differentiation are in italics. See text for details. Dotted arrowheads denote potential 'reverse' differentiation events. bFGF, basic fibroblast growth factor; bHLH, basic helix–loop–helix; BMP, bone morphogenetic protein; Cbfa1, core binding factor alpha 1; ECM, extracellular matrix; FGF, fibroblast growth factor; GDF, growth/differentiation factor; IBMX, 3-isobutyl-1-methylxanthine; LRP, low-density lipoprotein receptor-related peptide; MAPK, mitogen-activated protein kinase; PDGF, platelet-derived growth factor; SMAD, vertebrate homologue of Drosophila Mothers Against Decapentaplegic (MAD); TGF-β, transforming growth factor beta; WISP, Wnt-1-inducible protein.