sdl-1, a novel regulator of the Wnt pathway

The Wnt signaling pathway is a highly conserved cell signaling pathway that regulates cell fate determination and maintains adult stem cell populations, and when misregulated contributes to developmental defects and disease. In C. elegans, a variation of the Wnt pathway, the Wnt/-catenin asymmetry pathway regulates asymmetric cell division. Dishevelleds are cytoplasmic scaffolding proteins that function immediately downstream of the Wnt receptor and relay signals into the cell. In C. elegans, loss of both maternal and zygotic dishevelled-2 (dsh-2) function results in asymmetric neuroblast division defects and embryonic/early larval lethality, while loss of zygotic dsh-2 function disrupts asymmetric cell division of the somatic gonadal precursor cells (SGPs), Z1 and Z4. To identify genes that function with dsh-2 to regulate asymmetric cell division we undertook a genetic screen for dsh-2 suppressors. Over 60 suppressors were isolated, and we have focused our analysis on two of these (suppressors of dsh-2 lethality), Sdl-1(hk164) and Sdl-1(hk245). We determined that both were dominant suppressors and suppressed all dsh-2 phenotypes. Mutations in other Wnt pathway components involved in asymmetric cell division, including lin-17/Frizzled and mig-5/Dishevelled, are also suppressed by sdl-1. Through genetic mapping experiments and whole genome sequencing we identified both suppressors as mutations in W04A8.6. hk245 is a mutation in the 7th and last exon of sdl-1 and results in a Glutamic Acid to Lysine change, while hk164 is found in the 6th exon and results in a Leucine to Phenylalanine change. sdl-1 is an essential gene with no homology outside of nematodes, and there is no sequence information that lends insight into its function. We have shown that SDL-1::GFP is expressed in the embryo and is concentrated at the cell cortex in a subset of cells. There is no change in the subcellular localization of the suppressor, SDL-1(hk245)::GFP. Evidence indicates that levels of SDL-1(hk245) are two-fold higher than the wild type protein. We hypothesize that increased protein levels in sdl-1(hk245) may contribute to dsh-2 suppression. Our results indicate that sdl-1 is a novel Wnt pathway interactor.