Practice question

P6.p receives maximal LIN-3/EGF signal due to proximity directly underneath gonadal anchor cell, activating high MAPK MPK-1 and inhibiting LIN-1 repressor via phosphorylation. This induces primary lineage: three rounds of division generating eight cells forming central vulval rings vulE and vulF creating precise lumen for egg passage. Descendants express egl-17 fibroblast growth factor, cdh-3 cadherin, zmp-1 metalloprotease. P6.p also expresses DSL ligands APX-1, LAG-2, DSL-1 to activate LIN-12 Notch in neighboring P5.p and P7.p promoting secondary fate and preventing adjacent primaries, acting as organizer.