UNC-6 (netrin) stabilizes oscillatory clustering of the UNC-40 (DCC) receptor to orient polarity.
Bottom Line: By performing live-cell imaging of the DCC orthologue UNC-40 during anchor cell invasion in Caenorhabditis elegans, we have found that UNC-40 clusters, recruits F-actin effectors, and generates F-actin in the absence of UNC-6 (netrin).Together, our data suggest that UNC-6 (netrin) directs polarized responses by stabilizing UNC-40 clustering.We propose that ligand-independent UNC-40 clustering provides a robust and adaptable mechanism to polarize toward netrin.
Affiliation: Department of Biology, Duke University, Durham, NC 27708.Show MeSH
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Mentions: The interplay of positive and negative feedback is important in robust polarization responses in yeast (Howell et al., 2012; Bendezú and Martin, 2013; Dyer et al., 2013; Wu and Lew, 2013). Given that MADD-2 regulates this balance with UNC-40 clustering, we hypothesized that madd-2 mutants may show defects in UNC-40 polarization toward UNC-6. To test this idea, we examined F-actin and UNC-40 polarization toward endogenous UNC-6 in madd-2 mutants. Notably, UNC-40 and F-actin were no longer tightly localized to the invasive cell membrane of the AC in madd-2 mutants (Fig. 7, F and G). Furthermore, in contrast to the robust localization of F-actin along the invasive cell membrane in wild-type animals (n = 10/10 ACs; Fig. 8, A–C; and Video 5), time-lapse analyses revealed that madd-2 mutants often had transient, mislocalized patches of F-actin along the AC’s apical and lateral domains (n = 6/12 animals; Fig. 8, D–F; and Video 5). The specific function of MADD-2 in regulating UNC-6–independent UNC-40 clustering and the perturbation in UNC-40 polarization toward UNC-6 in madd-2 mutants offer compelling evidence that ligand-independent UNC-40 (DCC) clustering is required for robust polarization toward UNC-6 (netrin).
Affiliation: Department of Biology, Duke University, Durham, NC 27708.