Necessity and contingency in developmental genetic screens: LIN-3, Wnt and semaphorin pathways in vulval induction of the nematode Oscheius tipulae

摘要: Genetic screens in the nematode Caenorhabditis elegans identified EGF/Ras and Notch pathways as central for vulval precursor cell fate patterning. Schematically, anchor secretes EGF, inducing P6.p to a 1° fate; turn induces its neighbors 2° through Delta-Notch signaling represses Ras signaling. In Oscheius tipulae , successively then fates. Here we report on molecular identification of mutations affecting induction O. . A single Induction Vulvaless mutation was found, which identify cis -regulatory deletion tissue-specific enhancer lin-3 homolog, confirmed by CRISPR/Cas9 mutation. contrast this predictable mutation, resulting an excess fates unexpectedly correspond plexin/semaphorin pathway, not implicated C. Hyperinduction P4.p P8.p these mutants likely results from mispositioning cells due lack contact inhibition. The third pathway found forward genetics is Wnt pathway: decrease activity loss competence induction, miscentering P5.p. Our suggest that EGF have qualitatively similar activities albeit with quantitative differences effects This study highlights both necessity contingency genetic screens.