Crumbs organizes the transport machinery by regulating apical levels of PI(4,5)P2 in Drosophila.

Johanna Lattner,Marko Brankatschk,David Flores-Benitez,Elisabeth Knust,Weihua Leng

doi:10.7554/elife.50900

Johanna Lattner, Marko Brankatschk + Show 3 more

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https://doi.org/10.7554/elife.50900

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Abstract

An efficient vectorial intracellular transport machinery depends on a well-established apico-basal polarity and is a prerequisite for the function of secretory epithelia. Despite extensive knowledge on individual trafficking pathways, little is known about the mechanisms coordinating their temporal and spatial regulation. Here, we report that the polarity protein Crumbs is essential for apical plasma membrane phospholipid-homeostasis and efficient apical secretion. Through recruiting βHeavy-Spectrin and MyosinV to the apical membrane, Crumbs maintains the Rab6-, Rab11- and Rab30-dependent trafficking and regulates the lipid phosphatases Pten and Ocrl. Crumbs knock-down results in increased apical levels of PI(4,5)P2 and formation of a novel, Moesin- and PI(4,5)P2-enriched apical membrane sac containing microvilli-like structures. Our results identify Crumbs as an essential hub required to maintain the organization of the apical membrane and the physiological activity of the larval salivary gland.

Highlights

Epithelia can organize as layers or tubes, which form barriers and separate internal biological compartments from the environment
In support of the idea that Crb is necessary for efficient apical secretion, we found that glycoprotein secretion is impaired upon loss of Crb or Sdt, as revealed by intracellular retention of peanut-agglutinin-GFP (PNA-GFP, Figure 1-figure supplement 1O,P and II,JJ), which can bind to glycoproteins produced by the salivary gland (SG) (Korayem et al, 2004; Theopold et al, 2001; Tian and Hagen, 2007)
Our results point to two major components acting downstream of Crb that regulate secretion. i) We found that the Crb complex is essential for Rab6, Rab11- and Rab30

Summary

Introduction

Epithelia can organize as layers or tubes, which form barriers and separate internal biological compartments from the environment. Many epithelia are specialized for absorption or secretion by performing selective and directional transport of nutrients, enzymes and waste products, which is essential for metazoan life (Cereijido et al, 2004; Rodriguez Boulan and Macara, 2014; Lemaitre and Miguel-Aliaga, 2013) To perform these functions, epithelial cells are highly polarized: plasma membrane proteins and lipids are distributed asymmetrically into an apical domain facing the environment or a lumen, and a basolateral domain that contacts the neighboring cell and/or a basal lamina. The FBM of Crb is important for βHeavy-Spectrin (βH-Spec) recruitment to the apical plasma membrane, and thereby supports the polarized organization of the membrane-associated cytoskeleton (cytocortex) (Wodarz et al, 1995; Richard et al., 2009; Pellikka et al, 2002; Lee et al, 2010; Lee and Thomas, 2011; Médina et al, 2002b)

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