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PDF, English Download (11MB) | Lizenz: Functional characterization of flat clathrin lattices during endocytosis and cell migration by Bucher, Delia Lisa underlies the terms of Creative Commons Attribution 4.0

Abstract

Clathrin is a unique scaffold protein, which forms polyhedral cages at the plasma membrane. Adaptor proteins recruit clathrin to the plasma membrane where the triskelion-shaped clathrin units interact with each other and assemble into flat and curved lattices. The function of the curved clathrin-coated pits in forming clathrin-coated vesicles via dynamin-dependent scission during endocytosis is well studied. On the contrary, the role of the flat hexagonal clathrin arrays remains ambiguous and has been a controversial topic for decades. In this PhD thesis, we used different microscopic techniques (live-cell confocal microscopy, stimulated emission depletion nanoscopy, transmission electron microscopy, correlative light and electron microscopy) combined with mathematical modelling or micrometre-scale manipulation of substrates to unravel the role of flat clathrin lattices during two cellular processes: 1) Endocytosis and 2) Cell migration. 1) We describe a novel clathrin-coated pit formation mechanism in which clathrin arrays first assemble as flat clathrin-coated structures until they reach around 70 % of the final clathrin content. At that point a change in the adaptor/clathrin ratio marks the conversion from a flat to curved lattice and further addition of clathrin triskelia leads to the creation of a complete and invaginated clathrin-coated pit. We could show that the flat-to-curved transition of the clathrin coats is sensitive to the biophysical properties of plasma membrane and can be block by elevated plasma membrane tension. 2) We found a so far undescribed spatial relation between disassembling focal adhesions and newly forming larger flat clathrin lattices, called clathrin-coated plaques, during cell migration. We demonstrated that clathrin-coated plaques containing the extracellular matrix receptors integrins are generated at topographical cues of remodelled extracellular matrix and regulate cell migration as novel adhesive unit. These specific functions put a new focus on the poorly understood flat clathrin coats and highlight the multiple cellular applicability of clathrin arrays.