Figure 4. Treatments with the H⁺/K⁺ATPase inhibitor omeprazole phenocopy inhibition of Notch signaling.

A, Phenotype of control embryos and of embryos treated as indicated at late gastrula and at pluteus stages. DAPT, omeprazole-treated embryos and Delta morpholino injected embryos develop with a smooth archenteron that lacks delaminating secondary mesenchymal cells at late gastrula stage and that are albinos at pluteus stage. The black arrowhead shows pigment cells embedded in the ectoderm of control embryos. B, Whole mount in situ hybridization with mesodermal or endodermal molecular markers. The expression of the Delta target genes gcm, papss, and gata1/2/3 in the non-skeletogenic mesoderm territory is abolished in DAPT-treated and in omeprazole-treated embryos. In contrast, Delta, msp130 and foxA are expressed at normal levels in the skeletogenic primary mesenchymal cell precursors or endodermal precursors in DAPT-treated, omeprazole-treated or Delta morpholino injected embryos. Vegetal pole views of control and treated embryos are shown in the upper corners. Note, that the expression of foxA in the Delta Morpholino injected embryos and in the DAPT or omeprazole treated embryos, has expanded towards the vegetal pole, consistent with the absence of mesodermal precursors in these embryos. SB, swimming blastula; MB, mesenchyme blastula. Embryos are in frontal views. C, Luciferase assays with the Notch reporter RBP-JK. Omeprazole strongly inhibits Notch signaling induced by overexpression of Delta but has no effect on Notch signaling induced by overexpression of NEXT or NICD.