Reversible blockage of membrane retrieval and endocytosis in the garland cell of the temperature-sensitive mutant of Drosophila melanogaster, shibirets1.

Abstract

Temperature-induced structural changes in the cortical region of the garland cell, which is considered to be active in endocytosis, were investigated in a temperature-sensitive, single gene mutant of D. melanogaster, shibirets1 (shi) and wild-type (Oregon-R). At 19.degree. C, both shi and wild type showed similar structural features: an irregularly extended network of labyrinthine channels, coated pits and vesicles, tubular elements and .alpha. vacuoles. Tannic acid (TA) impregnation showed that coated pits comprised .apprx. 20-25% of the total coated profiles at 19.degree. C in both shi and wild-type. When flies were incubated in a horseradish peroxidase (HRP) solution for 5 min, organelles such as coated profiles, tubular elements, and .alpha. vacuoles were labeled. In wild-type at 30.degree. C, minor changes were observed, mainly a decrease in the distribution of the labyrinthine channels and an increase in HRP uptake. On the other hand, in shi at 30.degree. C, the labyrinthine channels were much elongated and their network became far more complex, indicating the expansion of the surface area of the cell. The coated profiles were increased in number while the number of tubular elements was decreased considerably. The TA method showed that almost all of the coated profiles were coated pits, coated vesicles being almost completely absent at 30.degree. C in shi. HRP uptake activity was considerably decreased at 30.degree. C. These structural changes, as well as the reduced HRP uptake activity, were reversible when the temperature was lowered to 19.degree. C. Evidently, in the garland cell of shi the conversion of coated pits to coated vesicles, that is, membrane pinch-off, is blocked at high temperature.