Coordination of adhesion and the actin cytoskeleton is critical in morphogenesis. Drosophila germband extension is a model for convergent extension. Canoe/afadin is found to have a novel role in this process. It helps to coordinate a contractile apical actomyosin network with cell shape change and regulates apical polarity protein localization.

During development, epithelial cells must generate and respond to tension without disrupting epithelial barrier function. The authors use superresolution microscopy in MDCK cells to examine how the zonula adherens (ZA) is remodeled in response to elevated contractility while maintain tissue integrity. They define key roles for zonula occludens family proteins in regulating contractility and for the scaffolding protein afadin in maintaining ZA architecture at tricellular junctions.

Platelet secretion is critical to hemostasis. Release of granular cargo is mediated by soluble NSF attachment protein receptors (SNAREs), but despite consensus on t-SNAREs usage, it is unclear which Vesicle Associated Membrane Protein (VAMPs: synaptobrevin/VAMP-2, cellubrevin/VAMP-3, TI-VAMP/VAMP-7, and endobrevin/VAMP-8) is required. We demonstrate that VAMP-8 is required for release from dense core granules, alpha granules, and lysosomes. Platelets from VAMP-8 ؊/؊ mice have a significant defect in agonist-induced secretion, though signaling, morphology, and cargo levels appear normal. In contrast, VAMP-2 ؉/؊ , VAMP-3 ؊/؊ , and VAMP-2 ؉/؊ /VAMP-3 ؊/؊ platelets showed no defect. Consistently, tetanus toxin had no effect on secretion from permeabilized mouse VAMP-3 ؊/؊ platelets or human platelets, despite cleavage of VAMP-2 and/or -3. Tetanus toxin does block the residual release from permeabilized VAMP-8 ؊/؊ platelets, suggesting a secondary role for VAMP-2 and/or -3. These data imply a ranked redundancy of v-SNARE usage in platelets and suggest that VAMP-8 ؊/؊ mice will be a useful in vivo model to study platelet exocytosis in hemostasis and vascular inflammation.

The small GTPase Rap1 and the actin-junctional linker protein Canoe/afadin are essential for the initial establishment of polarity in Drosophila, acting upstream of Bazooka/Par3 and the adherens junctions. However, feedback and cross-regulation occur, so polarity establishment is regulated by a network of proteins rather than a linear pathway.

Epithelial barrier loss is a driver of intestinal and systemic diseases. Myosin light chain kinase (MLCK) is a key effector of barrier dysfunction and a potential therapeutic target, but enzymatic inhibition has unacceptable toxicities. Here, we show that a unique domain within the MLCK splice-variant MLCK1 directs perijunctional actomyosin ring (PAMR) recruitment. Using the domain structure and multiple screens, we identified a domain-binding small molecule (Divertin) that blocks MLCK1 recruitment without inhibiting enzymatic function. Divertin blocks acute, TNF-induced MLCK1 recruitment as well as downstream MLC phosphorylation, barrier loss, and diarrhea in vitro and in vivo . Divertin corrects barrier dysfunction and prevents disease development and progression in experimental inflammatory bowel disease. Beyond applications of Divertin in gastrointestinal disease, this general approach to enzymatic inhibition by preventing access to specific subcellular sites provides a new paradigm for safely and precisely targeting individual properties of enzymes with multiple functions.