WAVE regulates Cadherin junction assembly and turnover during epithelial polarization

Abstract

Actin is an integral component of epithelial apical junctions, yet the interactions of branched actin regulators with apical junction components are still not clear. Biochemical data have shown that α-catenin inhibits Arp2/3-dependent branched actin. These results suggested that branched actin is only needed at earliest stages of apical junction development. We use live imaging in developing C. elegans embryos to test models for how WAVE-induced branched actin collaborates with other apical junction proteins during the essential process of junction formation and maturation. We uncover both early and late essential roles for WAVE in apical junction formation. Early, as the C. elegans intestinal epithelium becomes polarized, we find that WAVE components become enriched concurrently with the Cadherin components and before the DLG-1 apical accumulation. Live imaging of F-actin accumulation in polarizing intestine supports that the Cadherin complex components and branched actin regulators work together for apical actin enrichment. Later in junction development, the apical accumulation of WAVE and Cadherin components is shown to be interdependent: Cadherin complex loss alters WAVE accumulation, and WAVE complex loss increases Cadherin accumulation. To determine why Cadherin levels rise when WVE-1 is depleted, we use FRAP to analyze Cadherin dynamics and find that loss of WAVE as well as of the trafficking protein EHD-1/RME-1 increases Cadherin dynamics. EM studies in adults depleted of branched actin regulators support that WVE-1 maintains established junctions, presumably through its trafficking effect on Cadherin. Thus we propose a developmental model for junction formation where branched actin regulators are tightly interconnected with Cadherin junctions through their previously unappreciated role in Cadherin transport.

PTEN dephosphorylates Abi1 to promote epithelial morphogenesis

“…In Pten −/− EBs, increased amounts of Abi1 and excessive WRC activation may lock actin in the cell cortex and thus prevent epiblast differentiation and polarization. Furthermore, in the Caenorhabditis elegans intestinal epithelium, similar relocation of the WRC is suggested to facilitate the lateral movement of E-cadherin to the apical side and promote the assembly of apical adherens junctions (Sasidharan et al, 2018). Taken together, our data support the following hypothesis: during epiblast morphogenesis, PTEN dephosphorylates Abi1 and down-regulates the WRC at the cell cortex.…”

The Wave complex controls epidermal morphogenesis and proliferation by suppressing Wnt–Sox9 signaling

“…Previous work has demonstrated an important role for ABI1 (Ryu et al, 2009; Xiong et al, 2012) and the Wave complex (Lee et al, 2016; Sasidharan et al, 2018) in AJ homeostasis. The pattern of β-catenin immunostaining in Abi1 KD IFE had suggested that AJ formation was unaffected by the loss of Wave complex function (Fig.…”

Cadherin preserves cohesion across involuting tissues during C. elegans neurulation

“…To rule out the possibility that the lack of neuroectoderm involution is due to a lack of pharynx retraction, where HMR-1 is known to localize to its apical side ( Sasidharan et al, 2018 ), we measured the posterior movement of the anterior tip of the pharynx. Retraction is not significantly altered in any of the 12 hmr-1 mutant embryos assessed ( Figure 2c ), with an average of 17 microns involution in hmr-1 mutants vs 18 microns for WT.…”