Fig. 7
Suf/Spastizin regulates vesicle fission. (A) Electron micrographs of high-pressure frozen stage III oocytes. Cisternae with Clathrin coated buds accumulate in suf/spastizin oocytes (white arrowheads). Scale bar: 0.5 μm. (B–D) Stage III oocytes labeled with Clathrin (green; B, D) Dynamin (green; C, D) or MPA lectin (red; D). Clathrin and Dynamin localize to a subset of cortical granules. Note the accumulation of Dynamin on vesicles at the cortex in suf/spastizin oocytes (C). (E, F) Dynasore partially mimics the suf defect. Wt oocytes accumulate the cortical granule marker MPA-lectin (red) after treatment with Dynasore (E) similar to suf mutant oocytes (F). The huge compartment in the center of the Dynasore treated wt oocyte in panel E shows the germinal vesicle (oocyte nucleus). (G) Cortical granules continuously mature after ovulation. Stage V eggs were incubated with carrier (Co: upper row) or Dynasore (Dyn.; lower row) for 5, 15 or 30 min and then activated with H2O. The degree of chorion expansion correlates with Dynasore treatment duration. Note that the complete block of exocytosis also leads to opaque cytoplasm similar to suf mutants. (H) Working model for Souffle (red) function on immature secretory granules (ISG). Suf/Spastizin is necessary for the abscission of Clathrin-coated buds. Whereas the compartment matured into secretory, cortical granules (CG) with a dense-core, the Clathrin-coated vesicles enter the endolysosomal transport route probably to lysosomes. |