Jag1-Notch cis-interaction determines cell fate segregation in pancreatic development

The Notch ligands Jag1 and Dll1 guide differentiation of multipotent pancreatic progenitor cells (MPCs) into unipotent pro-acinar cells (PACs) and bipotent duct/endocrine progenitors (BPs). Ligand-mediated trans-activation of Notch receptors induces oscillating expression of the transcription factor Hes1, while ligand-receptor cis-interaction indirectly represses Hes1 activation. Despite Dll1 and Jag1 both displaying cis- and trans-interactions, the two mutants have different phenotypes for reasons not fully understood. Here, we present a mathematical model that recapitulates the spatiotemporal differentiation of MPCs into PACs and BPs. The model correctly captures cell fate changes in Notch pathway knockout mice and small molecule inhibitor studies, and a requirement for oscillatory Hes1 expression to maintain the multipotent state. Crucially, the model entails cell-autonomous attenuation of Notch signaling by Jag1-mediated cis-inhibition in MPC differentiation. The model sheds light on the underlying mechanisms, suggesting that cis-interaction is crucial for exiting the multipotent state, while trans-interaction is required for adopting the bipotent fate.

Jag1 Modulates an Oscillatory Dll1-Notch-Hes1 Signaling Module to Coordinate Growth and Fate of Pancreatic Progenitors

Notch signaling controls proliferation of multipotent pancreatic progenitor cells (MPCs) and their segregation into bipotent progenitors (BPs) and unipotent pro-acinar cells (PACs). Here, we showed that fast ultradian oscillations of the ligand Dll1 and the transcriptional effector Hes1 were crucial for MPC expansion, and changes in Hes1 oscillation parameters were associated with selective adoption of BP or PAC fate. Conversely, Jag1, a uniformly expressed ligand, restrained MPC growth. However, when its expression later segregated to PACs, Jag1 became critical for the specification of all but the most proximal BPs, and BPs were entirely lost in Jag1; Dll1 double mutants. Anatomically, ductal morphogenesis and organ architecture are minimally perturbed in Jag1 mutants until later stages, when ductal remodeling fails, and signs of acinar-to-ductal metaplasia appear. Our study thus uncovers that oscillating Notch activity in the developing pancreas, modulated by Jag1, is required to coordinate MPC growth and fate.