TCF3 (Transcription factor 3) is a transcriptional regulator, involved in the initiation of neuronal differentiation. Heterodimers between TCF3 and tissue-specific basic heli, Xenopus/Amphibian,-loop-heli, Xenopus/Amphibian, (bHLH) proteins play major roles in determining tissue-specific cell fate during embryogenesis, like muscle or early B-cell differentiation. Dimers bind DNA on E-bo, Xenopus/Amphibian, motifs: 5'-CANNTG-3'. Binds to the kappa-E2 site in the kappa immunoglobulin gene enhancer.