Responses to localized UV-laser irradiation are different between Bombyx and Drosophila eggs.

It has been found previously that in the silkworm, Bombyx mori, localized ultra-violet (UV) irradiation of eggs at as early as the fertilization stage could induce cuticle defects in resultant larvae. To compare the responses to the UV irradiation between Bombyx and Drosophila, embryos at various stages were irradiated with a scanning UV-laser microbeam (355 nm) over an area of 1.4-1.6% of the total egg surface. The results revealed that: (i) in Bombyx, embryonic mortality after irradiation was always low and independent of the stage of embryos at irradiation, while in Drosophila, the mortality was high at the cleavage stage and decreased as the development proceeded; (ii) in Bombyx, frequency of defective larvae after the irradiation was always high and independent of the stage of embryos at irradiation, whereas in Drosophila, high defect frequencies could be obtained only when irradiations were performed at or after the syncytial blastoderm stage; (iii) in Bombyx, the hypoderm surrounding the site of defect was always fused together to produce a continuous cuticle, while in Drosophila, the surrounding hypoderm was rarely fused together thus producing a hole in the cuticle; (iv) in Bombyx, the extent of the defects was constant from the fertilization through to the cellularization stage, whereas in Drosophila, the extent of the defects was largest at the cleavage stage and decreased as the development proceeded. These results suggest that there may be differences between the two insects in the mechanisms and/or the timing of embryonic pattern specification.