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The septin complex links the catenin complex to the actin cytoskeleton for establishing epithelial cell polarity
Xueying Wang1,2 , Wenwen Wang1,2,3 , Xiwei Wang1,2 , Ming Wang1 , Lijuan Zhu1,3 , Fatima Garba2 , Chuanhai Fu1,3 , Barbara Zieger4,* , Xu Liu1,2,* , Xing Liu1,3,* , Xuebiao Yao1,3
1MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics and Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230027, China
2Keck Center for Organoids Plasticity Control, Atlanta, GA 30310, USA
3Anhui Key Laboratory for Cellular Dynamics & Chemical Biology and CAS Center for Excellence in Molecular Cell Science, Hefei 230027, China
4Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg, 79106 Freiburg, Germany
*Correspondence to:Barbara Zieger , Email: barbara.zieger@uniklinik-freiburg.de Xu Liu , Email:lxu1016@ustc.edu.cn Xing Liu , Email:xing1017@ustc.edu.cn
J Mol Cell Biol, Volume 13, Issue 6, June 2021, Pages 395-408  https://doi.org/10.1093/jmcb/mjab036
Keyword: septin, cytoskeleton, cell polarity, adherens junction, epithelial cells

Cell polarity is essential for spatially regulating of physiological processes in metazoans by which hormonal stimulation‒secretion coupling is precisely coupled for tissue homeostasis and organ communications. However, the molecular mechanisms underlying epithelial cell polarity establishment remain elusive. Here, we show that septin cytoskeleton interacts with catenin complex to organize a functional domain to separate apical from basal membranes in polarized epithelial cells. Using polarized epithelial cell monolayer as a model system with transepithelial electrical resistance as functional readout, our studies show that septins are essential for epithelial cell polarization. Our proteomic analyses discovered a novel septin‒catenin complex during epithelial cell polarization. The functional relevance of septin‒catenin complex was then examined in three-dimensional (3D) culture in which suppression of septins resulted in deformation of apical lumen in cysts, a hallmark seen in polarity-deficient 3D cultures and animals. Mechanistically, septin cytoskeleton stabilizes the association of adherens catenin complex with actin cytoskeleton, and depletion or disruption of septin cytoskeleton liberates adherens junction and polarity complexes into the cytoplasm. Together, these findings reveal a previously unrecognized role for septin cytoskeleton in the polarization of the apical‒basal axis and lumen formation in polarized epithelial cells.