Cytoplasmic Cl− couples membrane remodeling to epithelial morphogenesis

Chloride is the major free anion in the extracellular space (>100 mM) and within the cytoplasm in eukaryotes (10 ∼ 20 mM). Cytoplasmic Cl− level is dynamically regulated by Cl− channels and transporters. It is well established that movement of Cl− across the cell membrane is coupled with cell excitability through changes in membrane potential and with water secretion. However, whether cytoplasmic Cl− plays additional roles in animal development and tissue homeostasis is unknown. Here we use genetics, cell biological and pharmacological tools to demonstrate that TMEM16A, an evolutionarily conserved calcium-activated chloride channel (CaCC), regulates cytoplasmic Cl− homeostasis and promotes plasma membrane remodeling required for mammalian epithelial morphogenesis. We demonstrate that TMEM16A-mediated control of cytoplasmic Cl− regulates the organization of the major phosphoinositide species PtdIns(4,5)P2 into microdomains on the plasma membrane, analogous to processes that cluster soluble and membrane proteins into phase-separated droplets. We further show that an adequate cytoplasmic Cl− level is required for proper endocytic trafficking and membrane supply during early stages of ciliogenesis and adherens junction remodeling. Our study thus uncovers a critical function of CaCC-mediated cytoplasmic Cl− homeostasis in controlling the organization of PtdIns(4,5)P2 microdomains and membrane remodeling. This newly defined role of cytoplasmic Cl− may shed light on the mechanisms of intracellular Cl− signaling events crucial for regulating tissue architecture and organelle biogenesis during animal development.