Description

The C. elegans vulva is formed from divisions of three vulval precursor cells (VPCs) – P5.p, P6.p, and P7.p – arranged along the anteroposterior axis in the ventral epithelium (Sulston and Horvitz, 1977). Previous analyses show the orientation of P5.p and P7.p descendants is determined by the interaction of multiple Wnt signals. egl-20/Wnt is expressed in the tail (Whangbo and Kenyon, 2000) and forms a posterior-to-anterior concentration gradient (Coudreuse et al., 2006). It has previously been shown that EGL-20 acts instructively during vulva development by imparting directional information, as opposed to being permissive, where it would only be required for polarization (Green et al., 2008; Minor et al., 2013). By moving the source of egl-20 expression from the posterior of the worm to the anchor cell, the axis of symmetry of the developing vulva, we can reorient the daughter cells of P5.p and P7.p toward the center in a wild-type configuration.

Expression of egl-20 from the center of the axis of symmetry partially suppresses the lin-17(n671) phenotype (Green et al., 2008; Table 1). To test whether LRP-2 acts downstream of EGL-20, we ectopically expressed egl-20 from the anchor cell in a lin-17(n671); lrp-2(gk272) double mutant background and compared it to a lin-17(n671); lrp-2(+) strain. If LRP-2 acts downstream of EGL-20, then anteriorly-expressed EGL-20 will not be able to suppress the lin-17 phenotype, with is the result observed (Table 1). Thus, like CAM-1 and VANG-1, LRP-2 likely acts downstream of EGL-20.