TheDrosophilaAfadin and ZO-1 homologues Canoe and Polychaetoid act in parallel to maintain epithelial integrity when challenged by adherens junction remodeling

Abstract

During morphogenesis, cells must change shape and move without disrupting tissue integrity. This requires cell–cell junctions to allow dynamic remodeling while resisting forces generated by the actomyosin cytoskeleton. Multiple proteins play roles in junctional–cytoskeletal linkage, but the mechanisms by which they act remain unclear. Drosophila Canoe maintains adherens junction–cytoskeletal linkage during gastrulation. Canoe’s mammalian homologue Afadin plays similar roles in cultured cells, working in parallel with ZO-1 proteins, particularly at multicellular junctions. We take these insights back to the fly embryo, exploring how cells maintain epithelial integrity when challenged by adherens junction remodeling during germband extension and dorsal closure. We found that Canoe helps cells maintain junctional–cytoskeletal linkage when challenged by the junctional remodeling inherent in mitosis, cell intercalation, and neuroblast invagination or by forces generated by the actomyosin cable at the leading edge. However, even in the absence of Canoe, many cells retain epithelial integrity. This is explained by a parallel role played by the ZO-1 homologue Polychaetoid. In embryos lacking both Canoe and Polychaetoid, cell junctions fail early, with multicellular junctions especially sensitive, leading to widespread loss of epithelial integrity. Our data suggest that Canoe and Polychaetoid stabilize Bazooka/Par3 at cell–cell junctions, helping maintain balanced apical contractility and tissue integrity.

Afadin regulates actomyosin organization through αE-catenin at adherens junctions

“…The studies in Drosophila showed that canoe regulates the maintenance of AJs in some morphogenetically active cells, but not in steady-state cells ( Sawyer et al, 2009 ). In addition, recent studies revealed that afadin or canoe plays critical roles for the dynamic regulation of AJs ( Choi et al, 2016 ; Manning et al, 2019 ). Therefore, afadin may play especially important roles in the maintenance of AJs and the proper actomyosin organization at AJs where the cell dynamics and force in tissue are elevated.…”

The Physical Mechanisms ofDrosophilaGastrulation: Mesoderm and Endoderm Invagination

“…For example, the leading edge of the epidermis during Drosophila dorsal closure has a repeated pattern of myosin 2 localization that resembles "bars-on-a-string," with each bar representing a single leading edge cell (Franke et al 2005). Recent super-resolution microscopy of leading edge cells has shown that Ena-a protein that promotes F-actin plus end elongation-localizes to the adherens junctions, suggesting that F-actin plus ends are enriched facing outwards from a central myosin 2 bar (Manning et al 2019). Given that leading edge cells have centrally localized myosin 2 and peripherally enriched F-actin plus ends, this topology again resembles a sarcomere.…”

ASPP2/PP1 complexes maintain the integrity of pseudostratified epithelia undergoing remodelling during morphogenesis

“…Similarly to previous work 26 , we also find no bias towards cell divisions orientated in the plane of the epithelium, suggesting that, at these early stages of Our results highlight the previously underappreciated localisation of ASPP2 at tricellular junctions in epithelial cells, in particular of the epiblast, and reveal the unknown biological function of ASPP2/PP1 complexes in the regulation of F-actin organisation at the apical junction. Considering that Afadin regulates the architecture of tricellular junctions in response to tensions 31,47 , the interaction between Afadin and ASPP2 strongly suggests that ASPP2 may exert its F-actin function at tricellular junctions via Afadin. The role of Afadin in regulating the linkage between F-actin and junctions during apical constrictions 48 suggests that ASPP2 may also be important in this process, which may be particularly relevant in the primitive streak.…”