Unique and redundant β-catenin regulatory roles of two Dishevelled paralogs during C. elegans asymmetric cell division

Abstract

The Wnt/β-catenin signaling pathway is utilized across metazoans. However, the mechanism of signal transduction, especially dissociation of the β-catenin destruction complex by Dishevelled proteins, remains controversial. Here, we describe the function of the Dishevelled paralogs DSH-2 and MIG-5 in the Wnt/β-catenin asymmetry (WβA) pathway in Caenorhabditis elegans, where WβA drives asymmetric cell divisions throughout development. We find that DSH-2 and MIG-5 redundantly regulate cell fate in hypodermal seam cells. Similarly, both DSH-2 and MIG-5 are required for positive regulation of SYS-1 (a C. elegans β-catenin), but MIG-5 has a stronger effect on the polarity of SYS-1 localization. We show that MIG-5 controls cortical APR-1 (the C. elegans APC) localization. DSH-2 and MIG-5 both regulate the localization of WRM-1 (another C. elegans β-catenin), acting together as negative regulators of WRM-1 nuclear localization. Finally, we demonstrate that overexpression of DSH-2 or MIG-5 in seam cells leads to stabilization of SYS-1 in the anterior seam daughter, solidifying the Dishevelled proteins as positive regulators of SYS-1. Overall, we have further defined the role of Dishevelled in the WβA signaling pathway, and demonstrated that DSH-2 and MIG-5 regulate cell fate, β-catenin nuclear levels and the polarity of β-catenin regulation.

The benefits of local depletion: The centrosome as a scaffold for ubiquitin-proteasome-mediated degradation

“…3 SYS-1/b-catenin is a transcription factor acting downstream of the Wnt signaling pathway to activate target genes necessary for cell fate specification. [75][76][77][78][79][80][81][82] During asymmetric division, SYS-1 is targeted to mitotic centrosomes by its interaction with the centrosomal protein RSA-2. 83 Disrupting SYS-1 centrosomal localization by depletion of RSA-2 leads to increased SYS-1 retention by daughter cells after division, indicating the presence of a negative regulatory mechanism involving centrosomal targeting.…”

Wnt Signaling Polarizes C. elegans Asymmetric Cell Divisions During Development

“…To analyze the effects of Dvl mutation on APR-1 function, we examined the levels and localization of SYS-1 (to assay the SYS-1-regulating pool of APR-1) and WRM-1 (to assay the WRM-1-regulating pool of APR-1). Consistent with Dishevelled’s role as a positive regulator of Wnt/β-catenin signaling, Dvl double mutants show symmetrically decreased nuclear SYS-1 in seam cell daughter nuclei while Dvl overexpression shows increased SYS-1 (Baldwin et al, 2016). However, a positive role regulating SYS-1 levels would suggest that Dvl mutants would have a symmetric loss of seam cell fate, rather than the confused or randomized polarity that is observed.…”

“…To our surprise, we found that cortical PRY-1::GFP is symmetric throughout the cell cycle and both daughters are born with high levels of cortical PRY-1 (Baldwin et al, 2016). The finding that PRY-1/Axin is symmetrically localized during L4 seam cell divisions begs the question of how PRY-1 drives asymmetric localization of APR-1/.…”

“…Each daughter cell carries different nuclear, cytoplasmic and cortical localization profiles of the determinants of WβA pathway, as observed by the addition of fluorescent tags (Mizumoto and Sawa, 2007a). The asymmetric localization of negative regulators of the pathway such as APR-1 and PRY-1 can be observed at the anterior cortex while positive regulators such as Frizzled (MOM-5) and Dishevelled proteins (DSH-2 and MIG-5) are distributed to the posterior cortex of the mother seam cell as well as the early embryo (Park et al, 2004, Baldwin et al, 2016, Mizumoto and Sawa, 2007a, Park and Priess, 2003). The asymmetric cortical localization of negative determinants to the anterior cortex is regulated by Wnt ligands as demonstrated by observing APR-1/APC and PRY-1/Axin localization in mutants lacking Wnt ligand EGL-20 (Mizumoto and Sawa, 2007a).…”

“…Dishevelled (Dvl) in particular seemed a likely suspect due to its role as a gatekeeper for the various Wnt signal transduction pathways including Wnt/β-catenin, Wnt/PCP, and Wnt/Calcium (Sokol, 1999, Wallingford and Mitchell, 2011, King et al, 2009, Hingwing et al, 2009). Loss of two C. elegans Dvl paralogs, dsh-2 and mig-5 , causes relatively mild changes to overall seam cell numbers but gaps and doublets appear in the seam cell A-P distribution suggested randomized cell fate that resulted in some symmetric divisions (Banerjee et al, 2010, Baldwin et al, 2016). Indeed, APR-1 is mislocalized to the both the anterior and posterior cortex of Dvl mutant seam cells, indicating that Dvl restricts the inheritance of negative regulators to the anterior daughter.…”