Ptf1a control of Dll1 reveals an alternative to the lateral inhibition mechanism

To determine if endodermal Notch activation and Hes1 expression depends on Dll1 activity, we analyzed NICD expression in wild-type and Dll1lacZ/lacZ embryos and EGFP expression in crosses of Tg(Hes1-EGFP)1Hri and Dll1lacZ/+ mice. NICD expression was reduced in E10.5 Dll1lacZ/lacZ embryos compared with controls (Fig. 2A,B), but appeared to recover, approaching wild-type levels at E11.5 (Fig. 2C,D). Hes1-EGFP expression was normal in E8.25 Dll1lacZ/lacZ embryos (Fig. 2E,I) but had partly disappeared from the dorsal pancreas endoderm at E9.5 (Fig. 2F,J) and was almost lost at E10.5 (Fig. 2G,K). Remarkably, and coinciding with the reappearance of NICD, Hes1-EGFP expression was restored in E11.5 Dll1lacZ/lacZ embryos (Fig. 2H,L). Development 139, 4492 (2012) doi:10.1242/dev.090597 © 2012. Published by The Company of Biologists Ltd