Graded distributions of netrin and semaphorin guidance cues convey instructive polarity information to migrating cells and growth cones, but also have permissive (i.e. non-polarity determining) functions in mammalian development and repair. The permissive functions of these cues are largely uncharacterised at a molecular level. We found previously that UNC-6 (netrin) signals permissively through UNC-40 (DCC) and UNC-5 receptors to prevent anterior displacement of the ray 1 sensillum in the C. elegans male tail. UNC-6/UNC-40 signalling functions in parallel with SMP-1 (semaporin 1)/PLX-1 (plexin) signalling to prevent this defect. Here, we report that a deletion allele of pvf-1, which encodes a VEGF-related protein, causes no ray 1 defects, but enhances ray 1 defects of a plx-1 mutant, and unexpectedly also suppresses unc-6(ev400)-null mutant ray 1 defects. These mutant ray 1 inductive and suppressive effects are mimicked by the ability of unc-40(+) and ced-10(gain-of-function) multi-copy transgene arrays to induce ray 1 defects or suppress unc-6 mutant ray 1 defects, depending on their dosage, suggesting the pvf-1 mutation causes UNC-40 overactivity that interferes with signalling but is partially sensitive to UNC-6. Additional data suggest PVF-1 functions through four VEGF receptor-related proteins and inhibits only CED-10 (a GTPase), but not MIG-2-dependent UNC-40 activity, even though UNC-40 functions through both GTPases to position ray 1. pvf-1 and receptor mutant ray 1 defects are rescued by transgenes expressing mouse VEGF164 and human VEGF receptors, respectively. These data report the first case of VEGF-induced inhibition of the netrin signalling and a molecular conservation of VEGF function from worms to humans.
Keywords: Crosstalk; GTPase; PVF-1/VEGF; UNC-40/DCC.