Which signaling molecule from P2 influences ABp fate?
At 4-cell stage, dorsal ABp and ventral EMS-P2 contacts establish ABa versus ABp asymmetry. P2 presents Delta-like ligands APX-1 and LAG-2, which bind GLP-1 Notch receptor highly expressed on ABp membrane, owing to par-3 mediated receptor localization. GLP-1 activation cleaves intracellular domain, activating Notch targets in ABp and repressing ABa-specific genes. Thus GLP-1 functions as instructive receptor transducing P2 positional information. Ablation of P2 or glp-1 mutants cause ABp to adopt ABa fate, producing symmetrical pharynx pattern, confirming Notch-mediated signaling from P2 determines dorsal-ventral distinction of AB lineage.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: GLP-1 Notch signaling from P2 influences ABp fate.