SYNCHRONIZED ENDOCYTOSIS STUDIED IN THE OOCYTE OF A TEMPERATURE-SENSITIVE MUTANT OF DROSOPHILA-MELANOGASTER

This study demonstrates that endocytosis in the oocyte of Drosophila melanogaster is reversibly blocked at the stage of pit formation by the temperature-sensitive, single-gene mutant, shibirets1. Uptake of horseradish peroxidase conjugated with wheat-germ agglutinin was observed to be normal in mutant oocytes at 19°C, but was blocked at 29°C. After 10 min at 29°C, there was a build-up of coated pits along invaginations of the plasma membrane. Also, the endosomal compartment consisting of tubules, bulbs, and small yolk spheres, disappeared. Lowering the temperature to 19°C after 10 min at 29°C released a synchronized wave of endocytosis into a cytoplasm cleared of uptake-related organelles. By observing this synchronized wave after exposure to 19°C for varying durations, we determined that endocytosis proceeds as follows: coated pits/vesicles→tubules→small yolk spheres→mature yolk spheres. The observations suggest that these organelles transform one into another within this sequence. © 1990 Springer-Verlag.