Kumari Kamalesh,1,2 Nadav Scher,2 Tom Biton,1,2 Eyal D. Schejter,1 Ben-Zion Shilo,1,∗ and Ori Avinoam2,3,∗∗
"1Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
2Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel"
"Exocrine secretion commonly employs micron-scale vesicles that fuse to a limited apical surface, presenting an extreme challenge for maintaining membrane homeostasis. Using Drosophila melanogaster larval salivary glands, we show that the membranes of fused vesicles undergo actomyosin-mediated folding and retention, which prevents them from incorporating into the apical surface. In addition, the diffusion of proteins and lipids between the fused vesicle and the apical surface is limited. Actomyosin contraction and membrane crumpling are essential for recruiting clathrin-mediated endocytosis to clear the retained vesicular membrane. Finally, we also observe membrane crumpling in secretory vesicles of the mouse exocrine pancreas. We conclude that membrane sequestration by crumpling followed by targeted endocytosis of the vesicular membrane, represents a general mechanism of exocytosis that maintains membrane homeostasis in exocrine tissues that employ large secretory vesicles.
On-section fluorescence microscopy was performed using Olympus IX83 microscope controlled via VisiView software (Visitron Systems GmbH) and equipped with a CoolLED pE-4000 light source (CoolLED Ltd., UK), 60x 1.4 NA and 100x 1.49 NA oil immersion objectives, and a Prime 95B sCMOS camera (Photometrics).
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The pE-4000 Universal Illumination System offers 16 selectable wavelengths from 365 - 770 nm, making it a highly flexible illuminator covering a wide variety of fluorophores
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