We characterized the tension response of clathrin-mediated endocytosis by using various cell manipulation methodologies. Elevated tension in a cell hinders clathrin-mediated endocytosis through inhibition of coat initiation, elongation of clathrin coat lifetimes and reduction of high-magnitude growth rates. Actin machinery supplies an inward pulling force necessary for internalization of clathrin coats under high tension. These findings suggest that the physical cues cells receive from their microenvironment are major determinants of clathrin-mediated endocytic activity.

Ferguson et al. demonstrate that clathrin coat growth rates can be utilized as quantitative reporters of clathrin-mediated endocytic dynamics in cellular contexts where errors associated with single-particle tracking are significant. They validate the tool within tissues of Drosophila embryos.

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Cellular processes associated with spatiotemporal changes in membrane mechanics induce significant alterations in clathrin-mediated endocytosis dynamics. This phenomenon is also observed during morphological changes shaping embryo development.

The most represented components of clathrin-coated vesicles (CCVs) are clathrin triskelia and the adaptors clathrin assembly lymphoid myeloid leukemia protein (CALM) and the heterotetrameric complex AP2. Investigation of the dynamics of AP180-amino-terminal-homology (ANTH) recruitment during CCV formation has been hampered by CALM toxicity upon overexpression. We used knock-in gene editing to express a C-terminal–attached fluorescent version of CALM, while preserving its endogenous expression levels, and cutting-edge live-cell microscopy approaches to study CALM recruitment at forming CCVs. Our results demonstrate that CALM promotes vesicle completion upon membrane tension increase as a function of the amount of this adaptor present. Since the expression of adaptors, including CALM, differs among cells, our data support a model in which the efficiency of clathrin-mediated endocytosis is tissue specific and explain why CALM is essential during embryogenesis and red blood cell development.