Early transcription factor that plays a key role in somitogenesis, paraxial mesoderm development and regulation of stem cell pluripotency. Essential for the mesenchymal to epithelial transition associated with somite formation. Required for somite morphogenesis, thereby regulating patterning of the axial skeleton and skeletal muscles. Required for proper localization of somite epithelium markers during the mesenchymal to epithelial transition. Also plays a key role in regulation of stem cell pluripotency. Promotes pluripotency exit of embryonic stem cells (ESCs) by priming ESCs for differentiation. Acts as a key regulator of self-renewal of hematopoietic stem cells (HSCs) by mediating HSCs quiescence and long-term self-renewal. Together with MEOX2, regulates transcription in heart endothelial cells to regulate fatty acid transport across heart endothelial cells. Acts by forming a heterodimer with another helix-loop-helix (bHLH) protein, such as TCF3/E12, that binds DNA on E-box motifs (5'-CANNTG-3') and activates transcription of target genes. Heterodimer; efficient DNA binding requires dimerization with another bHLH protein, such as TCF3/E12. Interacts with MEOX2.