High temperature‐induced changes in morphology in imaginal disc cells of a temperature sensitive lethal mutant of Drosophila melanogaster

A temperature sensitive lethal allele of suppressor forked in D. melanogaster, I(I)su(f) ts67g (1–65.9), was used to study the relation between the imaginal disc ability to evaginate and the temperature sensitivity of the mutant. The imaginal leg discs of larvae shifted up to 30°C early in development are unable to evaginate at this temperature either in vivo or in vitro. Furthermore, after four days at 30°C, the discs are unable to evaginate when the larvae are shifted back to 25°C. On the bases of gynandromorph analysis and the in vitro evagination experiments we conclude that the absence of evagination is autonomous. No abnormal cell death is found in the discs, indicating that the failure to evaginate is not a direct result of cell degeneration. After four days at 30°C some morphological abnormalities were found in imaginal disc cells. Annulate lamellae appear in the cytoplasm, the ribosomal packing and the microtubular character of the imaginal disc cells are also altered. We suggest that a defective proliferation is involved in the formation of this phenotype since mitotic cells were also found after the prolonged heat treatment.