Semaphorins are extracellular proteins that regulate axon guidance and morphogenesis by interacting with a variety of cell surface receptors. Most semaphorins interact with plexin-containing receptor complexes, although some interact with non-plexin receptors. Class 2 semaphorins are secreted molecules that control axon guidance and epidermal morphogenesis in Drosophila and C. elegans. We show that the C. elegans class 2 semaphorin MAB-20 binds the plexin PLX-2.
plx-2 mutations enhance the phenotypes of hypomorphic
mab-20 alleles but not those of
mab-20 null alleles, indicating that
plx-2 and
mab-20 act in a common pathway. Both
mab-20 and
plx-2 mutations affect epidermal morphogenesis during embryonic and in post-embryonic development. In both contexts
plx-2 null mutant phenotypes are much less severe than
mab-20 null phenotypes, indicating PLX-2 is not essential for MAB-20 signaling. Mutations in the ephrin
efn-4 do not synergize with
mab-20, indicating EFN-4 may act in MAB-20 signaling. EFN-4 and PLX-2 are coexpressed in the late embryonic epidermis where they play redundant roles in MAB-20 dependent cell sorting.