MDFI is a transcription factor that negatively regulates other myogenic family proteins. Studies of the mouse homolog, I-mf, show that it interferes with myogenic factor function by masking nuclear localization signals and preventing DNA binding. Knockout mouse studies show defects in the formation of vertebrae and ribs that also involve cartilage formation in these structures. MDFI an also interfere with the DNA-binding activity of Myod family members and plays an important role in trophoblast and chondrogenic differentiation.