SURFACE CAP MODIFICATIONS IN COLD-TREATED DROSOPHILA-MELANOGASTER EMBRYOS

When early Drosophila embryos were allowed to develop at 0-degrees-C, several abnormalities in the surface cap organization were observed. Scanning electron microscopy showed that exposure to cold mainly lead to the deformation of the cortical caps and to their partial fusion with adjacent caps. The process of cellularization was presumably affected and large uncellularized areas were observed. Rhodamine-phalloidin staining showed that cap deformation was closely related to the altered microfilament distribution, which was presumably responsible for the failure of large syncytial areas to cellularize. During the process of cellularization, F-actin localization did not depend on the microtubules forming the baskets around the elongating nuclei, but was related to the subpopulation of microtubules radiating from the centrosomes toward the plasma membrane. Only these microtubules seemed to be affected by cold treatment.