Shot and Patronin polarise microtubules to direct membrane traffic and biogenesis of microvilli in epithelia.

Ichha Khanal,Ahmed Elbediwy,Georgina C Fletcher,Maria Del Carmen Diaz De La Loza,Barry J Thompson

doi:10.1242/jcs.189076

Ichha Khanal, Ahmed Elbediwy + Show 3 more

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https://doi.org/10.1242/jcs.189076

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Abstract

ABSTRACTIn epithelial tissues, polarisation of microtubules and actin microvilli occurs along the apical-basal axis of each cell, yet how these cytoskeletal polarisation events are coordinated remains unclear. Here, we examine the hierarchy of events during cytoskeletal polarisation in Drosophila melanogaster epithelia. Core apical-basal polarity determinants polarise the spectrin cytoskeleton to recruit the microtubule-binding proteins Patronin (CAMSAP1, CAMSAP2 and CAMPSAP3 in humans) and Shortstop [Shot; MACF1 and BPAG1 (also known as DST) in humans] to the apical membrane domain. Patronin and Shot then act to polarise microtubules along the apical-basal axis to enable apical transport of Rab11 endosomes by the Nuf–Dynein microtubule motor complex. Finally, Rab11 endosomes are transferred to the MyoV (also known as Didum in Drosophila) actin motor to deliver the key microvillar determinant Cadherin 99C to the apical membrane to organise the biogenesis of actin microvilli.

Highlights

Cells in epithelial tissues are polarised and display distinct apical and basolateral membrane domains (Martin-Belmonte and Mostov, 2008; Rodriguez-Boulan and Macara, 2014; St Johnston and Ahringer, 2010; Tepass, 2012)
These Cadherin 99C (Cad99C)-positive microvilli are visible upon staining for filamentous actin (F-actin) or with transmission electron microscopy (TEM) (Fig. 1A–D)
Given that Rab11 endosomes are known to be involved in endocytic recycling to the apical membrane, as well as in trans-Golgi to plasma membrane exocytic delivery (Jing and Prekeris, 2009; Rodriguez-Boulan and Macara, 2014) and microvillus formation in enterocytes (Knowles et al, 2015), we examined their role in trafficking Cad99C to the apical membrane by inducing Rab11 RNA interference (RNAi) in follicle cells

Summary

Introduction

Cells in epithelial tissues are polarised and display distinct apical and basolateral membrane domains (Martin-Belmonte and Mostov, 2008; Rodriguez-Boulan and Macara, 2014; St Johnston and Ahringer, 2010; Tepass, 2012). How this fundamental apical-basal polarity is elaborated to direct the polarisation of all other features of epithelial cells remains a major unsolved problem (Nance and Zallen, 2011). In the case of the spectrin cytoskeleton, polarisation was first observed in Drosophila epithelial cells, where an apical β-Heavy (βH)-Spectrin subunit and basolateral β-Spectrin subunit segregate into complementary cortical domains (Lee et al, 1997; Thomas and Kiehart, 1994).

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