Endocytosis at Extremes: Formation and Internalization of Giant Clathrin-coated Pits Under Elevated Membrane Tension

Abstract

Internalization of clathrin-coated vesicles from the plasma membrane constitutes the major endocytic route for receptors and their ligands. Dynamic and structural properties of endocytic clathrin coats are regulated by the mechanical properties of the plasma membrane. Here, we used conventional fluorescence imaging and multiple modes of structured illumination microscopy (SIM) to image formation of endocytic clathrin coats within live cells and tissues of developing fruit fly embryos. High resolution in both spatial and temporal domains allowed us to detect and characterize distinct classes of clathrin-coated structures. For the first time, we show that membrane tension induces formation of giant coated pits (GCPs) that can be up to two orders of magnitude larger than the canonical clathrin-coated pits. GCPs take longer to form but their mechanism of curvature generation is the same as the canonical pits. We also demonstrate that GCPs can split into smaller fragments during internalization. Considering the supporting roles played by actin filament dynamics in clathrin-mediated endocytosis under mechanically stringent conditions, we suggest that local changes in the coat curvature driven by actin machinery can drive splitting and internalization of GCPs.

Tension-induced adhesion mode switching: the interplay between focal adhesions and clathrin-containing adhesion complexes

“…In the canonical scheme, clathrin, along with its adaptor proteins, creates curved and dynamic clathrin-coated pits to drive the internalization of membrane components, including FAs, through a process known as clathrin-mediated endocytosis (CME) (31)(32)(33)(34)(35). However, not all clathrin-coated structures (CCS) mature into pits and invaginate; some remain flat and reside on the membrane for long periods of time (36)(37)(38)(39)(40). These remarkably static and larger arrays of CCS are often termed as clathrin-coated plaques, flat clathrin lattices or clathrin sheets and exclusively localized on the ventral/adherent surface of cultured cell (29,41).…”