dictyNews

Electronic Edition

Volume 49, number 16

June 9, 2023



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Abstracts

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Formation and closure of macropinocytic cups in Dictyostelium



Judith E. Lutton1, Helena L. E. Coker2†, Peggy Paschke3†,

6 Christopher J. Munn4, Jason S. King4*, Till Bretschneider1* 

& 7 Robert R. Kay3*





Current Biology, in press



Macropinocytosis is a conserved endocytic process where cells 

engulf droplets of medium into micron-sized vesicles. We use 

light-sheet microscopy to define an underlying set of principles 

by which macropinocytic cups are shaped and closed in 

Dictyostelium amoebae. Cups form around domains of PIP3 

stretching almost to their lip and are supported by a specialized 

F-actin scaffold from lip to base. They are shaped by a ring of 

actin polymerization created by recruiting Scar/WAVE and 

Arp2/3 around PIP3 domains, but how cups evolve over time 

to close and form a vesicle is unknown. Custom 3D analysis 

shows that PIP3 domains expand from small origins,

capturing new membrane into the cup and crucially, that cups 

close when domain expansion stalls. We show cups can close 

in two ways: either at the lip, by inwardly-directed actin 

polymerization; or the base by stretching and delamination 

of the membrane. This provides the basis for a conceptual 

mechanism, where closure is brought about by a combination 

of stalled cup expansion, continued actin polymerization at the 

lip and membrane tension. We test this using a biophysical

model, which can recapitulate both forms of cup closure and 

explain how 3-dimensional cup structures evolve over time to 

mediate engulfment.





Submitted by Robert Kay [[log in to unmask]]

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[End dictyNews, volume 49, number 16]