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E‐cadherin has a fundamental role in epithelial tissues by providing cell–cell adhesion. Polarised E‐cadherin exocytosis to the lateral plasma membrane is central for cell polarity and epithelial homeostasis. Loss of E‐cadherin secretion compromises tissue integrity and is a prerequisite for metastasis. Despite this pivotal role of E‐cadherin secretion, the transport mechanism is still unknown. Here we identify Myosin V as the motor for E‐cadherin secretion. Our data reveal that Myosin V and F‐actin are required for the formation of a continuous apicolateral E‐cadherin belt, the zonula adherens. We show by live imaging how Myosin V transports E‐cadherin vesicles to the plasma membrane, and distinguish two distinct transport tracks: an apical actin network leading to the zonula adherens and parallel actin bundles leading to the basal‐most region of the lateral membrane. E‐cadherin secretion starts in endosomes, where Rab11 and Sec15 recruit Myosin V for transport to the zonula adherens. We also shed light on the endosomal sorting of E‐cadherin by showing how Rab7 and Snx16 cooperate in moving E‐cadherin into the Rab11 compartment. Thus, our data help to understand how polarised E‐cadherin secretion maintains epithelial architecture and prevents metastasis. [ABSTRACT FROM AUTHOR]

The Drosophila oogenesis system provides an excellent model to study the development of epithelial tissues. Here, we report the first genome-scale in vivo RNA interference (RNAi) screen for genes controlling epithelial development. By directly analysing cell and tissue architecture we identified 1125 genes, which we assigned to seven different functions in epithelial formation and homeostasis. We validated the significance of our screen by generating mutants for Vps60, a component of the endosomal sorting complexes required for transport (ESCRT) machinery. This analysis provided new insights into spatiotemporal control of cell proliferation in the follicular epithelium. Previous studies have identified signals controlling divisions in the follicle stem cell niche. However, 99% of cell divisions occur outside of the niche and it is unclear how these divisions are controlled. Our data distinguish two new domains outside of the stem cell niche where there are differing controls on proliferation. One domain abuts the niche and is characterised by ESCRT, Notch and JAK/STAT-mediated control of proliferation. Adjacent to this domain, another domain is defined by loss of the impact of ESCRT on cell division. Thus, during development epithelial cells pass through a variety of microenvironments that exert different modes of proliferation control. The switch between these modes might reflect a decrease in the 'stemness' of epithelial cells over time. [ABSTRACT FROM AUTHOR]

Intracellular trafficking of secretory proteins plays key roles in animal development and physiology, but so far, tools for investigating the dynamics of membrane trafficking have been limited to cultured cells. Here, we present a system that enables acute manipulation and real-time visualization of membrane trafficking through the reversible retention of proteins in the endoplasmic reticulum (ER) in living multicellular organisms. By adapting the "retention using selective hooks" (RUSH) approach to Drosophila , we show that trafficking of GPI-linked, secreted, and transmembrane proteins can be controlled with high temporal precision in intact animals and cultured organs. We demonstrate the potential of this approach by analyzing the kinetics of ER exit and apical secretion and the spatiotemporal dynamics of tricellular junction assembly in epithelia of living embryos. Furthermore, we show that controllable ER retention enables tissue-specific depletion of secretory protein function. The system is broadly applicable to visualizing and manipulating membrane trafficking in diverse cell types in vivo. [Display omitted] • RUSH enables the synchronization and visualization of membrane trafficking in vivo • It allows control of protein secretion in intact animals and cultured organs • It identifies the dynamics of the junction assembly in epithelia of living embryos • ER sequestration can be used to generate tissue-specific loss of function Glashauser, Camelo, et al. present a set of tools in Drosophila that enables synchronization and visualization of membrane trafficking in intact animals and cultured organs through reversible endoplasmic reticulum retention of secretory proteins. The system is broadly applicable for investigating membrane trafficking dynamics in vivo and depleting proteins for loss-of-function studies. [ABSTRACT FROM AUTHOR]