BackgroundDevelopment of the pancreas and the nervous tissues is regulated by common transcription factors. A basic helix‐loop‐helix protein, p48 of pancreas transcription factor 1 (PTF1), is essential for differentiation of the exocrine acinar cells.ResultsWe isolated PTF1 p48 from 9.5‐day mouse embryos as a binding protein of RBP‐Jκ, a mediator of Notch signalling. p48 bound to RBP‐Jκ more strongly than and in a distinct way from Notch1. In 9.5–12.5 day embryos, p48 was expressed in the dorsal part of the neural tube as well as in the pancreatic buds. Two lines of evidence suggested functions of p48 in neurogenesis: (i) expression of p48 was induced in P19 cells when they committed to neural fate upon retinoic acid treatment, and (ii) p48 over‐expressed in Xenopus embryos repressed the development of neuronal precursors. p48 inhibited the MASH1‐activated transcription from the E‐box, while p48 stimulated transcription from the PTF1 motif synergistically with E47. The p48/E47‐activated transcription from the PTF1 motif was stimulated further by RBP‐Jκ and RBP‐Jκ derivatives that mimicked the active RBP‐Jκ/Notch complex.ConclusionsIn developing embryos, p48 is expressed in both the nervous system and the pancreas. p48 inhibits neuronal differentiation. We propose possible mechanisms for this inhibition.