Dynamin recruitment and membrane scission at the neck of a clathrin-coated pit.
Bottom Line: The first is associated with coated pit maturation; the second, with fission of the membrane neck of a coated pit.A large fraction of budding coated pits recruit between 26 and 40 dynamins (between 1 and 1.5 helical turns of a dynamin collar) during the recruitment phase associated with neck fission; 26 are enough for coated vesicle release in cells partially depleted of dynamin by RNA interference.We discuss how these results restrict models for the mechanism of dynamin-mediated membrane scission.
Affiliation: Department of Cell Biology, Harvard Medical School, and Cellular and Molecular Medicine Program, Boston Children's Hospital, Boston, MA 02115 Department of Pediatrics, Harvard Medical School, Boston, MA 02115.Show MeSH
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Mentions: Scission of dynamin-coated membrane tubules in vitro requires that the tubule be under longitudinal tension (Roux et al., 2006; Morlot and Roux, 2013; Morlot et al., 2012; Bashkirov et al., 2008; Shnyrova et al., 2013). We examined the effect of membrane tension on the number of dynamin molecules that have accumulated at the time of coated vesicle release in SUM-Dyn2 cells expressing mCherry-LCa. Lowering plasma membrane tension by acute exposure to hyperosmotic medium inhibits coated vesicle formation (and the associated endocytosis of cargo; Heuser and Anderson, 1989; Morlot et al., 2012). Introduction of hyperosmolar medium (lowering membrane tension) caused the total number of dynamins to increase (Figure 7, A and B), suggesting that a flaccid membrane needs more dynamin to rupture than does a tense one. Nonetheless, cells incubated in hypo-osmotic medium (Boulant et al., 2011) and thereby subjected to a higher plasma membrane tension accumulated approximately the same number as did control cells (Figure 7, B–F). Thus there appears to be a threshold requirement for membrane scission, even when tension is unphysiologically high.
Affiliation: Department of Cell Biology, Harvard Medical School, and Cellular and Molecular Medicine Program, Boston Children's Hospital, Boston, MA 02115 Department of Pediatrics, Harvard Medical School, Boston, MA 02115.